Accurate Strong Gantry

[vargai]

Hello Everybody,

My target is to built a gantry for home use since I do office job and miss the miller work. (I have three sons so hope they follow the way)
The travel is 1000 x 700 x 250 mm with 1000 N cutting force in Plastic, AL, with 0,05 mm total accuracy.
After studying the relevant threads some contradiction still need to be solved.
I.e. my friend who build some CNC machines(not like this) says you only need one ball screw in the middle.
There are many ways but the proved, reported solution is my solution.
I hope with your help and skill I can reach my goal so please correct me where I am wrong.
Base is not finished in the attached figures.
My queries:

1500 mm long rail position-side or top ?
Is there any good carrige pattern to eliminate the double ball screw?
At belt synchronizing version1 or version2 is the better? -my logic says the equal belt length in any drive direction give more accuracy . http://www.mycncuk.com/attachment.php?attachmentid=13921&stc=1http://www.mycncuk.com/attachment.php?attachmentid=13922&stc=1http://www.mycncuk.com/attachment.php?attachmentid=13923&stc=1

Thank for your cooperation
BR
István

[EddyCurrent]

1. 1500 mm long rail position-side or top ?
2. Is there any good carrige pattern to eliminate the double ball screw?
3. At belt synchronizing version1 or version2 is the better? -my logic says the equal belt length in any drive direction give more accuracy .

1. As far as I'm aware the bearings and rail do not care which way you have them but you need to think about how you will mount them so that they are level with each other across the frame, and that they are the same distance apart along the frame.
2. On a 700 wide machine I think you will need 2 ball screws.
3. As you say, the equal belt length method looks best.

[vargai]

Thanks form the prompt answer,
[QUOTE
3. As you say, the equal belt length method looks best.[/QUOTE]

When I am saying equal length I am thinking of the extra synchronizing belt that has the same upper and lower length .
In the lower figure the drive is symmetrical so I am confused which of you mean the best

[vargai]

1. As far as I'm aware the bearings and rail do not care which way you have them but you need to think about how you will mount them so that they are level with each other across the frame, and that they are the same distance apart along the frame.

I am planning to machine the base in one operation with bearing in mind the cost so at the moment side mount seems stronger and safer for the rail

[EddyCurrent]

Thanks form the prompt answer,

3. As you say, the equal belt length method looks best.
When I am saying equal length I am thinking of the extra synchronizing belt that has the same upper and lower length .
In the lower figure the drive is symmetrical so I am confused which of you mean the best

Version 2 where the motor is central.

[Boyan Silyavski]

The price of the belt and pulleys will be same as the price for one driver more. So if you invest in one more motor you would have it properly made. Not that it would not work like that with one motor.

[vargai]

Thanks your comment, because this is one of the most critical issue here. You are aware of JazzCNC's intention namely two motor can cause big problem at synchronizing failure .
Just example for calculation with overestimated values:On a 1 m long belt 1 mm elongation on a perimeter of a 360 mm pulley gives 1 degree delay- derived to the 20/10 ball screw means 10 mm/360=0,027 mm deviation-looks not bad
But this is just theory again-reported data overrides the best theory.
I am planning to use 200-300 W servo here and master slave drive is quite expensive.
I saw you used two motors on your just made machine-I think steppers that gives torque protection but with potential step loss during operation
You know the target is 1000 N cutting force.
I need to see about this issue in the threads and your opinion is appreciated in the belt versus dual motor question.
Br
István

[Boyan Silyavski]

Hi, calculations are one thing, real life another. I have belt driven machine on all axis. So i believe i know something about belts. The only thing positive in this design is that the belt is perpendicular to the ball screw, means its not driving directly the machine but transferring the movement.

What size type belt and pulleys?

How heavy is the gantry with all motors, rails and so? Not sure if you could drive it with one 300w servo at all.

I know Dean /JazzCNC/ is driving his machine like this, but you have to make sure about the proper belt size, corresponding motor and make sure that the accumulated inertia of the pulleys and ball screws will not limit the machine speed.

And looking at 0.05mm means tthat you must strive at 0.01mm. That means cheap chinese pulleys will NOT work. Have that in mind. And if you need to lower the inertia you must buy expensive aluminum pulleys or custom made that small size. I have 20 crap pulleys laying around cause i thought they were a deal from aliexpress.

[Boyan Silyavski]

PS. It would be better if the spindle center is inside the bearings that move the gantry looked from side. Means you should offset a bit more the gantry to the back. You have to imagine that when all is mounted and weights what it weights the center of the weight must be in the center between the 2 bearing that move the gantry.

[vargai]

understood what you mean, just wanted to reach the perimeter of the machine table with the tool to have access for edge drilling that is advantage at high work piece -but this is not main issue.
When I think of a standard VMC the real heavy consoled spindle house running up and down on a vertical rails with about 400 mm or more offset and the bearings stands it- it is their job.
I am using 25 mm bearings that is IMO strong enough for normal operation, however I will consider your suggestion-every detail can be important.
Perhaps it will help to support the rail side form above against the constant torque and lowering the console lever according to your suggestion

[Boyan Silyavski]

When I think of a standard VMC the real heavy consoled spindle house running up and down on a vertical rails with about 400 mm or more offset and the bearings stands it- it is their job.

Yeah, but with sliding counter weight at the back to balance the weight of the head so at the end the bearings have less push when static than a gantry cnc

[vargai]

belt is common and useful item (coupling) between motors and ball screw reducing the dynamics and revolution with effect of the inertia -I saw it in the Hurco VMC as well that a had worked on earlier.
Short belt is accurate:long synchronizing belt -I do not know . The only thing is sure - producer gives 0,1-0,2 mm accuracy on a belt driven linear unit on 1 m long.(so the elongation is the accuracy)

You are right double ball screw means double inertia and its effect to the required power fourfold.
That is why I am here to overcome this type of doubt , so thank you to share your experience

[Boyan Silyavski]

According to the charts HTD 5M is well in the charts for what you will use it for. I would say 25mm wide and steel corded. I wouldn't go with other braids cause Kevlar and so stretches. Pulleys should be 20 - 22 teeth. Make the ball screws placement and design so that they are only long for the exact necessary travel. Dont overextend them cause its easier to mount or for other reason. Pulleys should have fitted bronze bushing and the bolts/shafts should be proper ones. Shoulder bolts if you use bolts and steel shafts, don't leave them to rotate without bearing in between.

PS, some additional info:
http://www.mycncuk.com/attachment.php?attachmentid=13925&stc=1
http://www.mycncuk.com/attachment.php?attachmentid=13926&stc=1


http://www.mycncuk.com/attachment.php?attachmentid=13927&stc=1

[vargai]

I am a fan of taper locks or similar shaft lock- simple fast and not expensive - is it good without parallel key?

[Boyan Silyavski]

Then you will need dial indicator and mess around just to center it properly on the shaft. Cause they are not self centering to the needed tolerance. Plus are heavy. Best would be tight fit and you or somebody localy to machine you the pulleys from aluminum.

[vargai]

thanks, already I can go further with design
BR
István

[JAZZCNC]

So if you invest in one more motor you would have it properly made. Not that it would not work like that with one motor.

It is properly made and it actually works better than twin motors being more accurate and reliable if done correctly.
My machine use this setup and I'm just going to upgrade and replace worn components and seen has this means new custom length belts and new gantry setup etc then it would be perfect opertunity to change to twin motor setup if it was better.? . . I can tell you now the thought never entered my head and I wouldn't entertain swapping to twin motors unless I could use servo's or Hybrid servo system with encoder feedback.

This doesn't mean Twin motor setup is bad or worse because it isn't if setup and run well within the motors speed curve. What it does offer or mean is piece of mind that you never loose sync or have racking issues. No chance of damage to screws if one motor stalls at high feeds etc. Easy to setup and square gantry and never changes after belts have settled down.
Less electronics to deal with etc and while more mechanical items they are very low maintenance and easily available.

There are very few negatives but with some Big positives and if I had any negs it would be belts look messy with more initial work involved and need covering but other than that nothing really and when settled down after a few weeks running they are fit and forget other than yearly maintenance check.

[Boyan Silyavski]

What i meant was, lets say it in other words- that if you don't have a machine shop at home or access to one, it seems more easy to do it with 2 motors, cause no money will be saved buying all that stuff from internet, postage, custom bores and so, plus later the very careful alignment. It could pay off if 1 servo instead of 2, money wise, but like you say Dean, servo is the good way to go with 2 motors. So at the end is just a personal preference. I simply don't like that long belts. In reality my small machine works in a lot of dust and never had any problem with the belts.

[JAZZCNC]

So at the end is just a personal preference. I simply don't like that long belts. In reality my small machine works in a lot of dust and never had any problem with the belts.

Yes Boyan it really does boil down to preference and components used not really so much money. My machine doesn't use belts based on money it's soley down to accurecy and repeatabilty/reliabilty within a budget based on using a stepper system.
Any machine using closed loop or some form of error catching setup Ie Servo's/encoders then I wouldn't use single motor and long belts etc.

Regards belt accuracy etc then to any belt/pulley doubters out there then just see this made with a 1300mm wide router with medium weight gantry.!


https://www.youtube.com/watch?v=wjDvimSdH8M

[vargai]

Silyavski, Dean,

Thanks for the comments.
This is the case when everybody has right.The proof of the pudding is in the eating. Dean likes his pudding and you like yours.
I will do my one and will taste it.
I am going to install two screws anyway and link them with belt-it seems more simple now than two servos-later it can be upgraded

[vargai]

Hi,
Incredibly detailed piece, very nice done.
The patterns are so sharp even in a mm .
What sort of material is it?

[vargai]

What i meant was, lets say it in other words- that if you don't have a machine shop at home or access to one, it seems more easy to do it with 2 motors, cause no money will be saved buying all that stuff from internet, postage, custom bores and so, plus later the very careful alignment. It could pay off if 1 servo instead of 2, money wise, but like you say Dean, servo is the good way to go with 2 motors. So at the end is just a personal preference. I simply don't like that long belts. In reality my small machine works in a lot of dust and never had any problem with the belts.

I red about dual drive on other sites and heard of several complaints- homing, running faiulre, etc. I also do not say it is wrong rather say it is an elegant solution but like anything it can get out of order.
If it is happens I can not find on heaven and earth in Hungary expert to repair or without being robbed.
So that is way I get closer to the things from the simple side and it will be a future development.

[JAZZCNC]

Hi,
Incredibly detailed piece, very nice done.
The patterns are so sharp even in a mm .
What sort of material is it?

Aluminium 6082T6 cut with a simple 90degree spot drill nothing fancy.

Regards the belts and cutting conditions let me just say my machine 99% of the time it's been built has cut nothing but aluminium and the belts are completely uncovered being exposed to millions of flying sharp and very hot chips so are working in the worst enviroment and I've only ever had to replace two belts. This wasn't because of wear it was because I left a pulley loose which fell off after adjustments for a bracket for sensing belt breakage. (It was a very good real world test of my new belt E-stop.!:ambivalence:)
The other I trapped and damaged moving the machine due to not being covered. (So do as I say, not do as I DO, and cover your belts from the start other wise it never get done.!!)

[vargai]

at first sight thought painted wooden, but it cannot be done so sharp

[JAZZCNC]

at first sight thought painted wooden, but it cannot be done so sharp

Yes probably because of poor video done with phone camera.! . . .Looks much better in real life and very shiny.

[Sven]

I have a similar set up just 90 mm wider. I would not do it again, setting it up without backlash is a pain.

Next one wil have a dual stepper, a leadshine easy servo, which is a stepper with encoder.

In this design I would box up the 4 beams so they become one, that is much stiffer.

[vargai]

Hi Sven,

Yes , the four box should be redesigned somehow, originally I wanted to tie the boxes with 3, 4 plates to work together after placing the
ball screw
What does the similar exactly-how did you make the synchronising?
Nothing is written in stone-just thought to skip the step with stepper and make higher grade machine but do not know too much about stepper.
I hear of lead shine and certainly stepper technology becomes better so if there is an reliable option instead the more expensive servo why not.
My friend who is member of a CNC DIY group made a 5axis machine with steppers for woodwork upon order.
They mates from the group says: everything is ok but why did not you use servos.
Probably stepper is undervalued in public awareness.

[Sven]

I have the second setup in your diagram, with the motor in the middle. It is impossible to get enough tension in the belt without putting big loads in the spindle bearings.
I added a guide to push the middle section of the belt above the motor to reduce floppiness. still not good.

[vargai]

So you are a doubter of using belt based on your experience.
Others have well working machine with this set up.
I am just an outsider at the moment, the best thing is to ask Dean to show a short video of a working machine .
Would you be so kind to do it, Dean?

[vargai]

I have the second set up in your diagram, with the motor in the middle. It is impossible to get enough tension in the belt without putting big loads in the spindle bearings.
I added a guide to push the middle section of the belt above the motor to reduce floppiness. still not good.
Let me know about the data bearing type, size, belt type, size and experienced phenomenon
angular bearing on drive side it can bear more load than single row
20/10 ball screw with Dia 15 machined end -bearing can hold let's say max 1 Tons here

[Boyan Silyavski]

Let me know about the data bearing type, size, belt type, size and experienced phenomenon
angular bearing on drive side it can bear more load than single row
20/10 ball screw with Dia 15 machined end -bearing can hold let's say max 1 Tons here


Hey,
no tons here!! You have to read well the belt documentation! Find the belt tension formula on Gates web, calculate the tension for your exact setup and then using guitar tuner / or app on your phone/ tension the belt to the proper tension . This is a must to do it properly.

So the force you apply is not tons. Lets say its the force i can apply with one hand and using as a lever say 15mm screw driver against the motor and the frame. With say 20-25cm screw driver i exceed that force and over tighten the belt easily. Of course i have done it at the beginning with tuner, but now just know how a properly tensioned belt feels and sounds.

That means you have to design it so that you could lever somehow the motor with a wrench , screw driver or make some tightening mechanism. That does not mean introducing unnecessary idlers and tensioners.


I have the second setup in your diagram, with the motor in the middle. It is impossible to get enough tension in the belt without putting big loads in the spindle bearings.
I added a guide to push the middle section of the belt above the motor to reduce floppiness. still not good.

Now if you have read what i posted before and belt documentation may be you don't have the proper belt cord or you have not designed it to be tensioned properly. I tension the belts with one hand only and a screwdriver or a wrench, using them as a lever against the frame. So if you don't have where to lever them, drill a hole and fix something to be used as a support for the lever.

So are you idlers bigger than 20 tooth pulley as per belts specification? Cause if they are smaller, misaligned or whatever not properly followed, may be thats the problem.

Yeah , i advised against long belts exactly cause people don't bother to read carefully 300 pages belts manual and maybe they miss something or do some basic mistake. Yeah, Deans machine works, but he has knowledge and experience so his machine is an example that there is no problem with the design, not that if say you, me or sb else could do it with the same success.

I will give you an example - Honestly how many people know point 6 below. About the idlers size and placement. Most people i have seen on the forums think that they could place idlers where they want and 99% of the idlers are made by 3x 608 bearings stuck together, which in diameter a much smaller than 20 tooth pulley/which is ok for 10mm wide belts but not 25mm as is this case/


Also look at number 4. The machine sides should be stiff enough.




What i mean is RTFM, do everything properly and all will be smiles and sunshine.


http://www.mycncuk.com/attachment.php?attachmentid=13940&stc=1

[vargai]

Hey,
no tons here!! You have to read well the belt documentation!

"bearing can hold let's say max 1 Tons here mean only it has a capability to hold it but I have never said there would be so big load.
I just want to understand Sven's problem.
At the moment I am watching and listening to collect the proofed working solutions in order to make a good design.
It is useful information that you shared, I wish I were there in building
I read and will read any documentation what is necessary.
Thanks you more and more people knows about point 6.

[vargai]

Next one wil have a dual stepper, a leadshine easy servo, which is a stepper with encoder.

Hi Sven,
I read a short 20 page long description of leadshine easy servo and did not find mentions of dual purpose.
Can you point to it ie. link or so?
Thanks
István

[Clive S]

Hi Sven,
I read a short 20 page long description of leadshine easy servo and did not find mentions of dual purpose.
Can you point to it ie. link or so?
Thanks
IstvánIs this the one you are thinking about as shown by Dean :- https://www.youtube.com/watch?v=ZMZdCcLQc4M

[vargai]

Thanks Clive,
I have finished watching it with sound off, complete it later.
As far as I know two standard steppers can simultaneously operate two ball screws
Hope listening to the narrator will make clear everything with easy servos

[Boyan Silyavski]

I was looking into the Hybrid servo from leadshine. There were some things that did not convince me:
-the price of drives and motors and all below combined cause at that price i jumped at top 400W second hand AC servos with drives.
-No AC, so still need a transformer, so rectifier circuit, ~45eur,transformer 80-90euro, time, shipping etc.
-basically the characteristics which are no better than normal stepper
-low encoder count

They could have gained me with absolute encoder for example.


I am not saying they are bad, just that according to me, and in my particular case, the servos seemed better option or stay with steppers. Still time will show, when the machine is ready.

[vargai]

Still time will show, when the machine is ready.
Thanks, yes I am not planning machine to motor, in fact I am planning the suit motor to the machine , but first I have to reorder the frame because
learned my expectation is to idealistic:angel: with this gantry desing generally.So I get back to the ground:ambivalence:

[vargai]

Hi,
I would like to know where is limit in weight with the moving gantry that can be drive on reasonable way.
My redesigned one is still 100 kg made of steel with a 18 kg motor just for cheking.
I don't think I can go below 80-90 kg.
I don't care if it requires 20-50 W more just pls advice if this is over sized for a general strong gantry
Thanks

[Boyan Silyavski]

The general opinion is that if >70kg you can not move it adequately with 2x3nm motors so you need bigger motors, which now puts you into position to find bigger but at the same time fast enough or go with servo, which to me seemed the better option.

Now i am looking back at your gantry design. What size are the profiles, why 4, why are not connected each other? Whats your idea there? At that size machine
2x 100x100x3 or 100x100x4 welded together with separation for ball screw or not /if back/ will be ideal. 100x100x3 weights ~9kg/m and the 4mm weights 12kg/m, So you co8uld still move that gantry by 2x3Nm nema 23

[vargai]

The general opinion is that if >70kg you can not move it adequately with 2x3nm motors so you need bigger motors, which now puts you into position to find bigger but at the same time fast enough or go with servo, which to me seemed the better option.

Now I am looking back at your gantry design. What size are the profiles, why 4, why are not connected each other? Whats your idea there? At that size machine
2x 100x100x3 or 100x100x4 welded together with separation for ball screw or not /if back/ will be ideal. 100x100x3 weights ~9kg/m and the 4mm weights 12kg/m, So you co8uld still move that gantry by 2x3Nm nema 23

The modification is being processed hopefully more optimal now but from steel I have no to big margin with Z+Y plate gantry legs and all stuff (some item was hided on my dwg ) so it will be 100 kg anyway
When I saw my friend machine with the moving bed I said I would not want to move to and fro 120-150kg mass with material so it would be moving gantry.
Entering to this 700x1000 mm machining zone with rigid steel design I have to revise myself.
I am seriously thinking of the moving bed option now it is just 5-700 mm longer space and can forget many trouble i.e the dual motor, heavier spindle
My goal is a bit better an more accurate machine than a router so called semi industrial so within a 4000 -4500 GBP budget I would like to reach the best performance.

[JAZZCNC]

I am seriously thinking of the moving bed option now it is just 5-700 mm longer space and can forget many trouble i.e the dual motor, heavier spindle
My goal is a bit better an more accurate machine than a router so called semi industrial so within a 4000 -4500 GBP budget I would like to reach the best performance.

If you have the space then Fixed Gantry is the way to go without any doubt but the principle still applies regards motors and moving mass. There is nothing wrong with regular steppers if sized correctly and if used with quality Digital drives and external motion control card, which you would 100% require for servo's, then they won't lose position and will hold high accurecy without any encoders.

Regards Hybrid easy Servo's then I'm sat on the fence because while I know they work excellent I agree they are too expensive and Servo's can be bought for not much more money.! . . . BUT . . .And for some it's a very Big BUT.!! Servo's require more knowledge of setting up to get the best from them and can be nightmare to tune correctly, espicially if other electronics are not done correctly and noise is introduced has they are much less tolerant of noise in the system. (It's not uncommon for some one to turn on a dodgy radio or some noisey appliance and Servos take off at full speed.:whistle:)
I have seen people, experienced people, build machines or retro fit Mills with servo's only to change them at a later date with steppers because they can't get them running correctly or reliably. . . . Reliably being the key word.!! . . . . Now I'm not saying don't use servo's but I just mean be aware that they are not simple and can turnout to be more trouble than there worth for the inexperienced.
Hybrid easy servo's don't have this issue as they are essentially steppers with encoders for checking/correcting position.

Regards the machine I Try to always keep in mind the three most important goals of a CNC machine which in my opinion is accuracy, repeatabilty and finish quality.
Accuracy and repeatabilty comes from component quality and suitabilty along with machine ridgidity and attention to build.
Finish quality comes from some of the above but mostly from Ridgidity and machine design and while all three are important aspects the quality of finish is what I'm always aiming to improve. Achieving the best best finish quality is mostly about lessening tool deflection and chip clearence.
So if you can keep the tool stickout distance from spindle to a minimum and have the shortest Z axis extension you'll get the best possible result and it's here I'd look to improve machine design and in my opinion you won't go wrong if you follow this design. (which I'm sure he stole from my Head. :hysterical:) Just make a better, stronger Job and put proper spindle on it.:hopelessness:


https://www.youtube.com/watch?v=4Bj6er322Dg

[vargai]

you won't go wrong if you follow this design. (which I'm sure he stole from my Head. :hysterical:)

Bloody dual screw again!:excitement: Just kidding.
I am really happy to switched on the right track. Thank you.
Just interesting : he says at 6:37-in steel @9000rpm with HSS -can it be real?

[JAZZCNC]

Just interesting : he says at 6:37-in steel @9000rpm with HSS -can it be real?

Yes but didn't mention how long the tool lasted did he.!.:whistle:

[vargai]

Now i am looking back at your gantry design. What size are the profiles, why 4, why are not connected each other? Whats your idea there?

I will go on with the Fix gantry system because it is properly fit to my goal -the moving bridge is a big advantage and present for me- so I am not restricted with a fix bridge height.
However I do not want to cut this line and leave it this way.-probably I will make gantry with this principle too.
Some draft are attached with the gantry base solution.
I prefer to save the expensive, vulnerable parts
balls crew rail , belt drive so I tried to hide them next, behind or under the frame -I belive this is the best place for them against the impact of
-work piece uploading
-chips
-coolant
The other view is to apply the roof trusses principle where incredible small profile in a certain arrangement can form a very strong element.
In my dwg the three SQtube run along he perimeter tying to each other with reinforcement plates.
It is a pity I cannot check and compare the different version with software so only suppose it gives big torsion resistance to the frame





http://www.mycncuk.com/attachment.php?attachmentid=13993&stc=1 http://www.mycncuk.com/attachment.php?attachmentid=13995&stc=1
http://www.mycncuk.com/attachment.php?attachmentid=13994&stc=1

[Ross77]

Looks good but you might need a bit more triangulation. The thin gussets only work in one direction so ideally you need them in equal amounts in all 3 planes.

Why is there a bit gap in the middle?

What rails are you using? There are different types and some can handle 4 way loading and others cant so are best mounted on top of the rail. Espesially if you are using a heavy moving gantry.

[Boyan Silyavski]

Hi Vargai,
so you will go with moving gantry right? The way you have drawn the rails looks ok, but how you plan to straighten them and make them parallel?

[vargai]

Hi Vargai,
so you will go with moving gantry right?


I will go on with the Fix gantry system because it is properly fit to my goal -the moving bridge is a big advantage and present for me- so I am not restricted with a fix bridge height.
However I do not want to cut this line and leave it this way.-probably at a later time I will make gantry with this principle too.


The base frame version just idea for future project where the purpose and load let me use this principle.
Yes this is weak point of this design to achieve the straightness and parallelism
- correct more expensive method to machine it - can be done in one step w/o flipping the frame on the machine bed (drilling by DIY)
- DIY method:uncomfortableness: -I am sure you will invent it:sentimental:
By the way I am wonder about the cost of the
epoxy system comparing to the machining.
If you have access to earn money in mean time with other job I think machining cost can compete with DIY cost Sum.

[vargai]

Looks good but you might need a bit more triangulation. The thin gussets only work in one direction so ideally you need them in equal amounts in all 3 planes.

Why is there a bit gap in the middle?

What rails are you using? There are different types and some can handle 4 way loading and others cant so are best mounted on top of the rail. Especially if you are using a heavy moving gantry.

Yes some corrective action should be done .

The gap in the middle just represents the place of the single ball screw in case of narrower machine

regarding the rail I would use one like this which is regular type now
The problem is as you pointed to it at my case only the upper row of ball hold the load but the moment resistance is good that occurs at start-stop and direction change
I have no experience using it but suppose it works -the catalogue also mention it as possible mounting arrangement
http://www.mycncuk.com/attachment.php?attachmentid=14000&stc=1
Because of my 100kg+ heavy moving gantry I have drooped this design and go with fix gantry where the moving Z will be balanced

[Boyan Silyavski]

The Hiwin HGR are double row bearing blocks and there is no difference how you mount them, so don't worry about that.

For a router HGR20 is enough and even a bit overkill, depending on the design. So no worry here also.

[Ross77]

Ok, I'm a bit confused. You keep saying fixed gantry but then you show a bed with rails on the side.

Is this the bit that will be moving? If so I would have said that it is not the best way to do it. Moving beds should have the rails underneath and at approx. third points or a quater in.

That way the rails are supporting the load better and are closer together so you can get away with one ballscrew.

As you have drawn it the bed can bend in the middle under load.

[vargai]

Ok, I'm a bit confused. You keep saying fixed gantry but then you show a bed with rails on the side.

Sorry for being double meaning.
I have started the thread with the moving gantry principle and as the design and details developed according to the useful comment from the site two days ago especially after having Dean's #41 post I have changed my mind .
My intention was not to leave my earlier ne'er-do-well concept and correct it.
This is the case when the design concept turn to other way so I put this moving gantry into a drawer now and finish this chapter.
I will start a new thread with it when it is actual again.
So I am giving thanks everybody and I am at full pelt with the fix gantry from now on.:onthego:

[Boyan Silyavski]

Nevertheless keep this thread alive, cause that's one of the most interesting things, somebody starts with one idea that evolves in something quite different sometimes.

[vargai]

Chapter #2 Fixed gantry

I am back again after aging some thoughts however I could not go too far. I cannot find too much examples for the ideal fixed gantry frame.
Probably I am making the typical mistake and try to reform something that is good as it is.
My viewpoints are:
using hot rolled profile -do not know but think it is better vibration damper than cold formed tubes (SQ or RECT)
using bigger cross sections- to eliminate the bracing and welding as far as possible
setup with 1700 mm total length-just slightly longer than moving gantry

My concern are:

-bolted connection as figure shows-is it is good enough- instead of welding?

-The spindle overhang is quite big -though is fixed in one direction . Is there a better setup to eliminate?

-I would balance the moving bridge on both side with pneumatic cylinders or gas spring that I red here and like this option.
As the spindle moves in Y direction the Center of Gravity moves with it -that seems not too beneficial for the balancing

Figure below shows mainly principles first to make a good machine setup
http://www.mycncuk.com/attachment.php?attachmentid=14068&stc=1


Thank you for your comments and advice in advance.

[EddyCurrent]

My concern are:
-The spindle overhang is quite big -though is fixed in one direction . Is there a better setup to eliminate?

Double gantry or move the uprights to the end of the gantry, just some thoughts but I realise it might make the machine wider.

14069

[vargai]

Double gantry or move the uprights to the end of the gantry, just some thoughts but I realise it might make the machine wider.


Neither do I would make it wider.
The right figure with protruding plates or so with overlap the post could be good.
I do not assume real rigidity loos at Y axis when the rail ends are bolted only onto a strong plate.
I will make some detailing.
Thanks

[Ross77]

To get the best rigidity you need to keep the spindle inline with the support bearings so no overhang. You could rotate the rails so they are mounted end on and in the middle of the beam.

The vertical moving gantry beam looks a bit slender with regards to the end bearing spacing. I would guess its 200mm deep and 1000mm wide? Thats is not a good ratio for racking and I would make the most of the gantry height and increase the bearings to maximum so the moving beam is like 'H' shape.

That would naturally reduce the racking and take the pressure off the screws and rams.

Just how I would do it anyway :0)

[vargai]

To get the best rigidity you need to keep the spindle inline with the support bearings so no overhang.
Hope I understand well. I made a top view sketch (left figure) -I think the spindle can get much closer to the posts.
The higher H gantry beam is agreed.
Ideally it should be balanced like a VMC in the right figure- manufacturer apply 500-600 mm and more overhang without problem.
Theoretically a reversed moving balance can be done but it increases the mass on Y axis motor
There are tasks left.
http://www.mycncuk.com/attachment.php?attachmentid=14090&stc=1

[Ross77]

The spindle on a vmc has to be like that so the table can move. But the column is fixed and only the z axis moves. Don't get your designs mixed up, you have the opportunity to build some thing specific to your requirements so best look to optimise it.

If you want to get technical then you don't have to put the cutter directly in line with the bearing but you need to balance the y axis and put its centre of gravity in line with the rails as that will produce the smallest moment loading in the bearings and hence deflection.

I wasn't meaning to use a H beam but rather trying to explain the position of the beam relative to the vertical bearings, ie keep the beam 200mm deep but increase the bearing spacing To 400-500mm. Might need to draw something up.

[vargai]

Might need to draw something up.
Tried to catch the principle based on sketches but this is more complex and one detail can change the others.
Here are some slightly more detailed plans -the C/G is near the C/L of the horizontal ball screw so hope this setup works.


That would naturally reduce the racking and take the pressure off the screws and rams.

I have increased the bearing spacing-350 mm now.I do not think it is worse than a moving gantry since it has double Z screw. Forces on screws mainly come from the vertical feed force -assuming it about 200 N(??) while I would like to reach 1000 N machining force in the horizontal plane.
If something might be considered to apply one more shorter Z rail and +1 each carriage on both side-I do not know if it worth
Drilling only means center drilling in this machine and max 6-8 mm holes. The machining that requires Z force will be arranged in the middle zone of the table where the load is almost symmetrical on screws

Regarding to the profile I started to change them to bend opened ones from 6-8 mm thickness. All of them havv to be designed according to their function

By the way when I am taking about balancing I am thinking of the Z motor too. I want it to get relieved form beam mass. It cannot be balanced perfectly since the spindle is moving but I want to remove the dead load expect the spindle at least.

This vertical in-between railing makes me worry a little.
The implementation will not be too easy. At the moment I am planing to put together the Z frame from three bolted parts
http://www.mycncuk.com/attachment.php?attachmentid=14142&stc=1
http://www.mycncuk.com/attachment.php?attachmentid=14140&stc=1
http://www.mycncuk.com/attachment.php?attachmentid=14141&stc=1
http://www.mycncuk.com/attachment.php?attachmentid=14143&stc=1

[Ross77]

Looks good. I would probably extend the gantry uprights down to the floor so the more area would be available for welding and increase rigidity. the vertical rails could then drop down and increase the bearing spacing a bit more.

I think golden ratio is 2:1 so if the y axis is 800mm wide then you need 400mm bearing spacing. as you pointed out one change can affect another and you will need to look at flex in the mounting plates and possible bracing,


Do you think the gantry uprights need bracing as well? looks quite tall

It may have already been mentioned but how to plan to keep all the surfaces perfectly aligned whilst welding and given the surface tolerance on steel c section?

[vargai]

Looks good. I would probably extend the gantry uprights down to the floor so the more area would be available for welding and increase rigidity. the vertical rails could then drop down and increase the bearing spacing a bit more.

I think golden ratio is 2:1 so if the y axis is 800 mm wide then you need 400 mm bearing spacing. as you pointed out one change can affect another and you will need to look at flex in the mounting plates and possible bracing,


Do you think the gantry uprights need bracing as well? looks quite tall

It may have already been mentioned but how to plan to keep all the surfaces perfectly aligned whilst welding and given the surface tolerance on steel c section?


Extending the gantry uprights down seems good idea -this node should be rethink with the bracing and reinforcement plates in profiles.

My aim is to design parts that can be done by both DIY and machining method.
machine bad is Ok -it has surfaces to be leveled on top -preferably positioned on the same level-that is way stand the gantry leg here at the moment

Y beam is the same -can be done on both way

Z beams will be separated and bolted so it is similar to Y -I do not want to weld a U form and do something with frame -it makes my life hard
rather to make strong flange nodes and the careful assembly and adjustment will give the accuracy (especially the two parallel surfaces)
Nodes will be oriented and fixed with parallel pins.
That is only may plan for now -God knows nothing about it.

[JAZZCNC]

That design will be a night mare to build and setup which isn't required and will have no gain over other simpler designs. C channel is bad choice due to it being bendy/twisty in relation to boxsection.
I don't think you have really thought about the complexitys and realitys of building this design.?

The C section inner surfaces won't be flat so will need milling for the rails. Then you have the problem of making sure the uprights are perfectly parallel in 2 planes and perfectly perpendicular in the other.!! . . 99.9999999% Nailed on that you won't be able to weld this up and keep parallel/perpendicular in all planes.
Any surfaces that where milled flat and true won't be flat and true after welding so this will be a waste of time and you have no way mill when welded up.
There is a no provision for adjustment and the design is such that there is no room for any error to be taken out.

Boxsection will work far better and be much easier to setup or deal with alignment errors after welding.
The slight difference from ideal bearing loading which Ross suggested won't make any differance to the machine in real world performance or longevity but it will to your mental health and sanity when setting up.

Also the Uprights need far more bracing as any deflection here will show at the cutter and finish quality. Personally for best strength and bearing loading I would have double uprights each side of gantry with 1 rail on each upright and the uprights would be braced in 2 directions.

I feel If you go with this design you'll regret it come setting up time.!

[vargai]

99.9999999% Nailed on that you won't be able to weld this up and keep parallel/perpendicular in all planes.


I do not want to weld a U form and do something with frame -it makes my life hard


First of all thank you for giving me a 0,0000001 chance.
This is a design evolution process with analysis, checking, listening to the pointers . I am not able to put a ready for production plan on the desk right now and I am patient and have time. Bad design leads to a better one. (in a good case)
This is still a study where I try to find the place for all the function.

Some detail explained in written form and never meant to weld this construction otherwise I would need medical treatment right now.
Yes, box section is better than C no question-even when equipped with bracing
For some reason I supposed that box section is more inclinable to resonate than a thicker opened one
The stronger the better so I am opened to the closed section
Just a sketch about how I understood double upright braced in two direction

http://www.mycncuk.com/attachment.php?attachmentid=14153&stc=1

[Boyan Silyavski]

Now you have got me with that constant changing of the design. Why don't you like one design, stick to it and further develop it to suit your needs. If you liked the before suggested design from the video in post #41, then just see what is good and what could be bettered. i would suggest even contacting the guy and asking him if he were to make it again what he would change and what he liked. That will save you a lot of unnecessary trouble and give you invaluable real life feedback. Thats why people stick with certain designs, cause they are good and there is feedback.

I understand that the overhang of his design is bothering you, and it should be. Cause it bothering me. Not only the spindle, but the hole gantry overhangs. That kind of kills the good points of that particular design.

One thing from a design point of view people should understand is that the fixed gantry design we discuss here has one really strong point. I am sure most people don't understand this point properly. Its not that the gantry is fixed. Its that the rectangle it forms is very big so its moment of inertia is incredibly big. So when changing that fixed gantry design/where it forms a portal with 2 legs/ in any way that compromises it main strength is not a good idea.

Another basic point to understand is that all rests on a couple of bearing blocks in all 3 different coordinate planes. So no matter how strong you make the machine frame, the bearing spacing, placement and forces there will form the real weak spots.

the purpose of the strong frame is to hold enough for the forces. next purpose is to minimize bend and twist which leads to minimizing vibration.

What people fail to understand, i see it here and in the other forums, is that the machine frame should be sturdy to a certain point and then the aim should be to be integral. No need to make 1 ton machine when same could be achieved with integral 200kg one.

Sturdy machine that is extremely rigid will ring like crazy if not integral. So thats when all make them heavy instead of making the design integral.

By integral i mean designed so that all forces spread equally, neutralize themselves and no weak spots and overbuilds in any direction possible.


Thats why there are some principle designs that all use, cause they are integral. Not that always people take full use of the possibilities with that design.

I assure you that a properly designed L gantry will beat any day the fixed gantry design if its not properly designed.

And IMHO after playing a lot and rethinking all designs and reinventing the wheel, my conclusion is that if all things taken into account we must not forget that we usually use only 2.2 -3kw spindle, using only 6-12mm bits, so we should not forget the strongest point of each design and choose it when needed, cause at the end they will all work if made properly.

[Gotty101]

Im very new to this, but that was a great post silyavski.

[JAZZCNC]

And IMHO after playing a lot and rethinking all designs and reinventing the wheel, my conclusion is that if all things taken into account we must not forget that we usually use only 2.2 -3kw spindle, using only 6-12mm bits, so we should not forget the strongest point of each design and choose it when needed, cause at the end they will all work if made properly.

Now your getting what I've been trying to tell you for nearly last 2yrs. . .:toot: . . . . It gets even more stupid than just the spindle because half the time these massively over engineeered machines only ever cut wood or foam.!!! CRAZY

This design and the over hang are no problem what so ever.! . . Milling machines and Many large commercial horizontal designs use much much larger overhangs but rest of the machine is built to match.
Like Boyan rightly points out your design is weak where it matters most and not very well thoughtout in other areas. This why I would support and brace the uprights on 2 planes and support the gantry on 2 sides with rails.
The over hanging spindle wouldn't bother me in the slightest with correctly sized and spaced bearings. But if you want the best layout which is slightly more complex and costly then have the Axis which the spindle travels on supported both sides so effectively having a Box in Box arrangement.

Personally like Boyan says don't re-invent the wheel just make it fit your purpose.!!

[Ross77]

Well to be fair the first post did say 1000N cutting force so guessing big cutters will be used and with 0.05mm accuracy that's not much error budget within the whole machine.

Without getting in to complex design calcs the quickest and most economical solution is to over engineer the frame. The extra weight can be benificial and also a problem with regard to acel-decel and dynamic loading but this design stops all the loading being transferred to the x axis like a moving gantry. So wont be as much of a problem.

The natural progression of a diy machine is to upgrade so having a strong sturdy frame means you get bigger steppers or higher powered spindle at a later date.

I know that the machine will be limited by its spindle power and cutter diameter and in fact tool deflection will be the ultimate limiting factor to cutting and feed speeds but this isn't a commercial machine.

I always believe that the machine should be designed from the cutting tool back through the spindle and the rest of the machine. Maybe It would be better to start again with the design spec to confirm what spindle and cutters will be used and go from there. :0)

[Boyan Silyavski]

Now your getting what I've been trying to tell you for nearly last 2yrs. . .:toot: . . . . It gets even more stupid than just the spindle because half the time these massively over engineeered machines only ever cut wood or foam.!!! CRAZY

This design and the over hang are no problem what so ever.! . . Milling machines and Many large commercial horizontal designs use much much larger overhangs but rest of the machine is built to match.
Like Boyan rightly points out your design is weak where it matters most and not very well thoughtout in other areas. This why I would support and brace the uprights on 2 planes and support the gantry on 2 sides with rails.
The over hanging spindle wouldn't bother me in the slightest with correctly sized and spaced bearings. But if you want the best layout which is slightly more complex and costly then have the Axis which the spindle travels on supported both sides so effectively having a Box in Box arrangement.

Personally like Boyan says don't re-invent the wheel just make it fit your purpose.!!

Yeah Dean, i hear you now. Just needed to spend my first 1000kg of steel so i could understand you better :loyal:. You know, new toys, new experience...

[vargai]

Maybe It would be better to start again with the design spec to confirm what spindle and cutters will be used and go from there. :0)

I have changed the design and want to include the spindle being important( and heavy) part so the parameters:
3 kW motor + belt driven spindle with a later ATC option
Cutters "anything" that the motor can drive ( in plastic I can use 50 mm face mill :)
100-10000 rpm( so conventional machining range)
one option is AC motor +VFD -only the motor is 25 kg I know
other:s cheaper type servo motor or similar- designed for this purpose
I need some help in this subject to choose.
I made some searching but still have not find too much here.
Something I found on Blakburn's post but its reading is not aloud for small children.
So pls point it to if any is here
Thanks

[JoeHarris]

The C section inner surfaces won't be flat so will need milling for the rails. Then you have the problem of making sure the uprights are perfectly parallel in 2 planes and perfectly perpendicular in the other.!! . . 99.9999999% Nailed on that you won't be able to weld this up and keep parallel/perpendicular in all planes.

I feel If you go with this design you'll regret it come setting up time.!

This is so important when developing your design. I don't know how much experience you have welding? But things will distort and if you are just starting out you want to be able to weld in a flat position as much as possible. Building in adjustment is key - especially if building using limited equipment and skill. You can draw to crazy levels of accuracy but when it comes to drilling a hole or cutting to 0.1mm using the kit you have in your garage!???

With my cheap drill press, cut off saw and stick welder I have needed some tolerance building my frame and I have seriously taken my time!!!

You are doing the right thing sharing on here though you will get some v helpful advise.

[Boyan Silyavski]

Better read this Advice sought on new Mill build (http://www.mycncuk.com/threads/7921-Advice-sought-on-new-Mill-build)

What you need will be BT30 spindle+servo motor.+ATC attachment - all from China , Aliexpress


You should beef everything then considerably. This is a serious build for first one. It seems you still don't have it clear for what exactly will use the machine? Maybe an used mill /VMC/ will be best ?

[vargai]

You can draw to crazy levels of accuracy but when it comes to drilling a hole or cutting to 0.1mm using the kit you have in your garage!???
With my cheap drill press, cut off saw and stick welder I have needed some tolerance building my frame and I have seriously taken my time!!!
You are doing the right thing sharing on here though you will get some v helpful advise.

Thanks for the attention and care.
I have to share my inner motivations and means for the best understanding.
I.e. Silyavski thinks I bite off more than I can chew
I am amazed at the way you guys build very good machines.
As for me I want to apply machining where necessary.
Perhaps I am not the only one here with this. But personally I feel a pang of conscience because this is not really DIY method and do not know where is the border.

[Ross77]

What size cutters are you planning to use in alu? 50mm face on plastic wont generate much force.

Welding is you are all probably aware is an art in its self and you must only weld small sections at a time and move around the frame to reduce heat build up. Its slow but the only way to go.

You can design to minimise joints and increase contact area so spot welding can be used.

Is your model in AutoCAD? If so I could help out with the frame design. Hopefully increase strength and reduce the weight! :0)

[vargai]

What size cutters are you planning to use in alu? 50mm face on plastic wont generate much force.

Welding is you are all probably aware is an art in its self and you must only weld small sections at a time and move around the frame to reduce heat build up. Its slow but the only way to go.

You can design to minimise joints and increase contact area so spot welding can be used.

Is your model in AutoCAD? If so I could help out with the frame design. Hopefully increase strength and reduce the weight! :0)

I have downloaded some kind of study about machining force and my
goal on 1000 N is not oversized requirement. I hope I can use max DIA 10-12 mm with moderate technology and dia 30-35 face mill on same way.
The machine will give the right answer and I will give a "reluctant" acceptance to it. I do not care if some work take a while since I will use this machine on one off and small batch production. With good strategy and preparation I even can compensate it but not bother if not. I have a day time job so it will be a free time profitable passion.
Regarding the design I am rather analyst type and it is important and challenge for me to see the theory behind the result.
Everything happens according to some kind of theorem and if one catches the rule then catches the physical result.
So thank you for your help in advance.I still have to adjust my plan a bit and revert it later.
I use Solidworks but the estimating the elastic deformation (strength ) would be a big help too.

[Ross77]

Could you post a link to that cutting data? Some quote the force required to cut the material and the tangential force seen by each axis can be much lower. Those figures seem a bit high. Unfortunetly all my reference material is on my old pc so will have to dig it out.

What spindle do you plan to use? To a certain point the more powerful the spindle the lower the cutting force.

[Boyan Silyavski]

http://aluminium.matter.org.uk/content/html/eng/default.asp?catid=129&pageid=2144416345

Its very difficult to say the exact cutting force, having in mind it will vary with your tool sharpness, type, teeth count,rake angle,the type of aluminum, feed, rigidity of the machine.


Better use your common sense. Download and use the spread sheets here from the forum to calculate the machine stiffness at different points, use HSMAdviser or GWizard to calculate spindle HP and deflection at different settings. Make up your mind and choose what to do further.


But i still don't get why you dig so deep. Its so simple. You want to do all up to aluminum- make a router. You want to do iron, steel and so - make mill. Once you decide that, its a matter of choosing the design that fits you and realize it.

I don't see reason fitting mill head to router. Cause once you start that, you will finish with a mill.



Your initial design was spot on. Your gantry was weak. Fit a gantry similar to my second build/i am doing right now/ and i assure you you will reap through aluminum like butter. The yellow router i build /look signature/ reaps through 1mm of aluminum without turning on the spindle :hysterical:, like a knife passes through butter, without feeling it at all. Or follow Johnathans design where the gantry is split in 2 and the z is inside. That are proven designs that will work very well. A well build machine will hold better tolerances than cheap chinese mill.

You will very unlikely use 12mm bits with aluminum. Most possibly 3mm and 6mm. Cause aluminum is expensive to waste it with 12mm tools.


Not that i don't believe that for a first build you will not make it. I just know how much time a very good design needs. Mistake here and there will cripple considerably the capacity of the machine. Talking about machine made for metals i mean. Aluminum or no. I for once want somebody to make the mill as i envisioned the column in the suggested post. If you feel confident build the mill, it would be cheaper than suggested if you build the frame yourself. Hell, once i finish that big trunk i am building now, will build myself a mill.

[vargai]

Could you post a link to that cutting data? Some quote the force required to cut the material and the tangential force seen by each axis can be much lower. Those figures seem a bit high. Unfortunetly all my reference material is on my old pc so will have to dig it out.

What spindle do you plan to use? To a certain point the more powerful the spindle the lower the cutting force.
Thank you to correct me. I have just referred to it by heart and of course do not want to propagate false data
Here is the link and it says 40-50 N
http://www.ijens.org/103004-5151%20IJBAS-IJENS.pdf it is talking about HSM milling but use 1000rpm for this test ??

200-400 N is from a college measurement protocol where the matl is mild steel
the first is 10 mm flute mill

http://www.mycncuk.com/attachment.php?attachmentid=14288&stc=1

and the follow is face milling in mild steel

http://www.mycncuk.com/attachment.php?attachmentid=14289&stc=1

Sorry for digging too deep but I am confused about the new present day parameter used in Ali.
At my former job we machined Ali 20% of total and used empirical values in technology heard from colleagues and the owner of the shop. On that Hurco VMC we used max 4-5000 rpm (4-12mm 2 flute cutters) and as I see this is the lowest on router. Could you tell some practical values according to table above? It is not complicated but I am not confident in machining calculator but more familiar with practical data.

[vargai]

Its so simple. You want to do all up to aluminum- make a router. You want to do iron, steel and so - make mill.
Give me a little time to get my act together.
I have no the total budget now so step by step building. I could buy a pile of steel here Hungary for 2500 GBP so buying used machine is not my way.
This is not a summertime love with a Spanish Bonita and I am too old to make mistake.I have machined and built an A3 format router with TBA drive:hopelessness: two years ago and I would leave out some steps and would like to build this 1000x700x300 mm real machine.That's why I am perhaps too careful.
So to spill the beans : my intention is with this build beside the passion and joy for me and my sons is to make some kind of retire fund. In this I trust better than in Gov.
I can get jobs form my employer since we mainly do automation projects with cabinets and software but the give the machining to subcontractor for high price.
Regarding to the other job source as well I do not want to narrow my flexibility only to Al, plastic.
So let's say mainly Al, and plastic but with passable capability in steel.
I have used this word "steel in my introductions but I left it later seeing this is taboo at router.
When I look at the machining forces in the above post I think with 1000N one can provide acceptable performance in steel too acknowledging that this is not an intensive material removing machine.
Building a frame with resistance to this forces not impossible challenge and I am sure your yellow one is pretty stronger. Still believe in the above size the fixed gantry with improvement fits to my goal but I will study yours and Jonathan's .
As you pointed to it I am rather confused about the spindle but I have to draw the borderline soon.

[Boyan Silyavski]

The bottleneck of this project will be the spindle. So a certain realism should be applied when designing the machine.

Why? I agree that you could build a frame any style for a mill. And make it rigid enough.

You have exactly 3 general choices:

-use cheap Chinese water cooled spindle up to 3kw /2 phase/ or even bigger 4-5kw. 18-24k rpm. The problem is that the bearings of the spindle are not made for steel machining though from time to time you could do that. No low revolution power. I would never try to use mine spindle on steel

-Use the BT30 spindle 8000RPM from ali express. Now this spindle screams for column Z. Otherwise how you will mount the motor and the tool change and balance the weight? Not possible. Not so cheap though as only the spindle side will be >2000eur with the motor and changer. Not so fast for High speed machining


-use the design like the german gantry machine example and add bigger than 10kw spindle. That will work best for what you want but the spindle will be very expensive.


So as you see, it is like i said before- you want steel -you make a mill, you want up to aluminum -you make a router. You want both-yes it possible, but prepare some $$$, cause you will need BIG motor to be fast and at the same time to has power on the low rpm.

[JAZZCNC]

I agree 100% with everything Boyan says regards spindle but it just doesn't stop at the Spindle to do this correctly.

The massive build required to cut steel correctly with acceptable accurecy and repeatabilty affects the linear motion and motors used plus many other things. (Has Boyan knows well.!!)
Wood's plastics etc need higher feeds to cut correctly so this means motors which can handle high Mass of heavy gantry and still allow higher feeds.
This will mean servos to do it correctly. Servos require high pulse counts so this means quality motion control cards and control software. The list and expense goes on and up.

Has Boyan will no doubtly be very aware of this quickly gets expensive and requires more attention to detail and selection to get it correct.
Even then there will always be a compromise in the machine some where.? One machine can't do everything to high standards without being very very expensive.

IMO you will be much better building a router that will cut everything in it's capabiltys, Ie woods,plastics etc to a high standard.
Then buy a milling machine at later date that will do and give the same high accurecy and repeatabilty with Aluminium and Steel etc.

The chances of failure or dissapointment for large machine to cut steel is very high and the extra expense trying to do so easily wasted. Much better to be realistic about this just build a strong functional router and save the money you WILL waste trying to build all round machine then put it to buying a milling machine.

[vargai]

-Use the BT30 spindle 8000RPM from ali express. Now this spindle screams for column Z. Otherwise how you will mount the motor and the tool change and balance the weight? Not possible. Not so cheap though as only the spindle side will be >2000eur with the motor and changer. Not so fast for High speed machining

I have just went through the sites of motor, spindle, etc and they are expensive even from China.
Ie.only a BT40 spindle would be 2000 EUR in my hand with VAT,etc.
In my present eyes it is too much for 30 kg engineered steel and if I went with this I would make it myself.
Regarding the power I think I would satisfied with about 4 kW
But the main issue is not this and thank you to summarized.

[vargai]

IMO you will be much better building a router that will cut everything in it's capabiltys, Ie woods,plastics etc to a high standard.
Then buy a milling machine at later date that will do and give the same high accurecy and repeatabilty with Aluminium and Steel etc.


Years ago two gentlemen visited us from a UK company Built Offsite to clarify the details of some modular building.
Being interested and reading some books about inventors and Technics I told them that the industrial revolution did not begin accidentally in the UK.The only fortuitous was just they came from Shrewsbury where around the industrial revolution had begun.
You are enterprising and advised to reach the high technical level where you are now.
I hope I am enterprising enough no to stop at the difficulties and advised enough to perceive the realistic factors.

The cost is vulnerable issue and the question is over and above: what is different between machine and good machine and very good machine. Purpose+Design+cost+used time+effort and so on -there are many factors are too see and specify the scope.

[GEOFFREY]

Years ago two gentlemen visited us from a UK company Built Offsite to clarify the details of some modular building.
Being interested and reading some books about inventors and Technics I told them that the industrial revolution did not begin accidentally in the UK.The only fortuitous was just they came from Shrewsbury where around the industrial revolution had begun.
You are enterprising and advised to reach the high technical level where you are now.
I hope I am enterprising enough no to stop at the difficulties and advised enough to perceive the realistic factors.

The cost is vulnerable issue and the question is over and above: what is different between machine and good machine and very good machine. Purpose+Design+cost+used time+effort and so on -there are many factors are too see and specify the scope.

I do not usually comment on this type of thread, but PLEASE listen to Jazz. He knows exactly what he is talking about and trying to stop you spending money needlessly. Build a good quality router for softer materials and buy/convert a mill for steel. That is my lot, I shall not comment again in this thread. Good luck with whatever you decide. G.

[vargai]

I do not usually comment on this type of thread, but PLEASE listen to Jazz. He knows exactly what he is talking about and trying to stop you spending money needlessly. Build a good quality router for softer materials and buy/convert a mill for steel. That is my lot, I shall not comment again in this thread. Good luck with whatever you decide. G.
Thank you and you are welcome any time.

[JAZZCNC]

Years ago two gentlemen visited us from a UK company Built Offsite to clarify the details of some modular building.
Being interested and reading some books about inventors and Technics I told them that the industrial revolution did not begin accidentally in the UK.The only fortuitous was just they came from Shrewsbury where around the industrial revolution had begun.
You are enterprising and advised to reach the high technical level where you are now.
I hope I am enterprising enough no to stop at the difficulties and advised enough to perceive the realistic factors.

The cost is vulnerable issue and the question is over and above: what is different between machine and good machine and very good machine. Purpose+Design+cost+used time+effort and so on -there are many factors are too see and specify the scope.

I'm struggling a little here to decide if we have a language barrier thats getting the translation a little muddled or if you are saying "Get stuffed" I'll do it my way regardless.?

Hope it's just language differences but honestly I don't care if not.! . . . Because if your stupid enough to go against good sound advice from several experienced people then more FOOL you and I DON'T wish you Good luck as that would be encouraging someone to waste money and being a born & breed Yorkshire Man I wouldn't encourage even a FOOL to do that..:stupid: . . . . . Just like I won't waste my time or hard learnt experience on FOOLS.!

[Ross77]

Normally if someone says that it cant be done then that is like a red rag to a bull and I try to come up with a solution, but now you have brought steel into the equation then I would agree with the others that it will be really difficult as the requirements are at opposite ends of the spectrum.

If it was Diy the you could compromise on the design and use the machine to the best of its abilities but you seem to be saying that it will be a commercial use so that wouldnt really be feasible.

If you did proceed you will need to two spindles.

1. Low speed with high ridigity and power at low speed for steel.
2. High speed and power at high speed for ali.

You would then need 10mm pitch ball screws on high power servo motors with high resolution encoders to get the accuracy. Etc etc.

It can be be done but like the others have said it will be expensive and you will still end up compromising the design. It may well be cheaper and better from a production point of view to build 2 specific machines. Good luck

[vargai]

I'm struggling a little here to decide if we have a language barrier thats getting the translation a little muddled or if you are saying "Get stuffed" I'll do it my way regardless.?

Have I made something wrong?
I have started this thread and collected all the information that is necessary to make decision.
I have not buy anything and not gone any direction yet .
The only thing I do I try to make out these info that is just slightly more then just listening.

[vargai]

It may well be cheaper and better from a production point of view to build 2 specific machines. Good luck


IMO you will be much better building a router that will cut everything in it's capabiltys, Ie woods,plastics etc to a high standard.
Then buy a milling machine at later date that will do and give the same high accurecy and repeatabilty with Aluminium and Steel etc.

Sorry for late answering. I could have placed this post to a general thread since by going through my one the searching on the good design led the doubt about the primary aim.
Reading the posts after my latest design I recognized or at least felt the generally weak points. Sorry for seeming stubborn. It is not meant to happen. My tenacity is all about my goals and not the way and method to reach it. It is not easy to abandon a main intent and to say right away yes, or no.
So thank you all who involved for your efforts and advice in highlighting my weakness.
I hope I do not have to turn my back on metal and will be able to build a good router for Al and other softer material.

[GEOFFREY]

Hi, I said that I would not post again on this topic, but your final sentence sounds very sensible. G.

[Ross77]

Hi Vargai
Don't be put off building a machine, maybe you should proceed and prove us all wrong :o)

everyone is just trying to help you get the best results.

[vargai]

Hi Vargai
Don't be put off building a machine, maybe you should proceed and prove us all wrong :o)
everyone is just trying to help you get the best results.

Of course I do not , because the goal is not to prove that is impossible but to build what is possible:)
Let me ask something I have a doubt about.
I saw your latest general frame design and I am wonder how the steel hollow tube beams bracing react to the machining force on a router .(generally).The seems like "strings" and source of resonance but I have never seen or heard router during operation.
Actually I am wonder of the smallest applicable size ie 50x50x3 showed many times.

[Ross77]

It was meant as more of an idea than a finished design. Yes if the bracing became long and slender then it could resonate. They are all different lengths so they would have different resonant frequencies.

It is also the base frame so the bolting down fixings will help with damping.

Like I said it was more of a basic idea, I did quite a few different options and it started getting messy. So look at the bracing for layout and size accordingly.

I plan to build a similar heavy duty fixed gantry mill, better not mention that I want it to cut steel. He he

[GEOFFREY]

I plan to build a similar heavy duty fixed gantry mill, better not mention that I want it to cut steel. He he

With a smallish (600x400?) working area and a strong solid fixed gantry machine, I do not see why steel should be
too much of a problem. My machine (converted commercial PCB drill/router) had a steel section right across the middle of the aluminium table that was used to locate dowelled stacked boards for drilling etc. Careless use by the previous owners operatives has led to to both the alluminium and steel parts of the bed covered in holes and grooves all over the place!!! These have maily been cut with sub 1mm cutters, which probably did end up breaking, but not before inflicting serious scars everywhere. With a slower speed spindle, and the right cutter I feel sure that I could cut steel, but would not need to be greedy with regards to feed speed DOC etc. G.

[JAZZCNC]

With a smallish (600x400?) working area and a strong solid fixed gantry machine, I do not see why steel should be
too much of a problem. My machine (converted commercial PCB drill/router) had a steel section right across the middle of the aluminium table that was used to locate dowelled stacked boards for drilling etc. Careless use by the previous owners operatives has led to to both the alluminium and steel parts of the bed covered in holes and grooves all over the place!!! These have maily been cut with sub 1mm cutters, which probably did end up breaking, but not before inflicting serious scars everywhere. With a slower speed spindle, and the right cutter I feel sure that I could cut steel, but would not need to be greedy with regards to feed speed DOC etc. G.

Strong Fixed gantry machine is the correct choice for larger foot print when cutting steel with correct spindle attached. Moving gantrys will cut steel with correct spindle but are less than ideal unless massively built.
My router which in the grand scheme of things is weak compared to even lightest duty milling machine as cut steel on the odd occasion and even cast iron. But it's not really practicle or advisable as it knocks the stuffing out the machine and takes an age to cut due to restrictions on feed and DOC.

The whole reason or point of my objections is that one machine can't cut every material correctly and when comes to steel a moving gantry design is not practical due to the strength needed and all that it brings with it to the build. Far cheaper and easier to build/buy to separate machines each designed for it's purpose.

[vargai]

It was meant as more of an idea than a finished design.
It was not criticism just gathering data for a steel based light weight moving gantry DIY router that can be used in its scope and additionally I can check , try some solutions. I red about HSM spindle and HSM Al milling and aware of that this is also a wide spectrum so I will be happy with the result that a router can give.
Not forgetting the steel I am planning to attach an easy removable really small, geared spindle driven by the HS one with belt or directly coupled. (EDIT: i see now that the belt not good at this speed) In this method the supposed extension of the original spindle would be only about 60-80 mm and the force not bother the main spindle bearings
With 1:0,5 ratio (12000-to 6000 rpm) and quite enough torque I probably can make a typical steel milling with DIA 4-5 mm mill.
This would be making opening on a flat parts of electrical enclosures ( mainly doors) and mainly Dia 30,5 mm holes for push buttons.
The only problem is that the thickness is 2 mm but I suppose a 3kW spindle can do it with full DOC( the pre drilling- hydraulic method works but too slow and there are other shapes). This will not be bottleneck if I cannot do it just an idea.
pls adjust me if someone has experience.
One question about the steppers:
Normally they do their job and do not care of step loss and go on.
Is there any no too expensive mean, method to persuade them to stop at step loss and not multiply the mistake.
Thanks

[mitchejc]

I've run a stepper based machine for several years and when configured conservatively it will not loose steps under normal conditions. But if you are looking for something else maybe try EasyServo, its steppers that offer some of the features of servos but still easy to set up. Not sure about how the cost compares to the stepper motors you have in mind. They are basically steppers with build in encoders and run closed loop. They will try to correct lost steps and if they can't they would stop and give a fault signal it the error goes over a configurable amount of steps + some other cool features not really possible on other steppers without encoders. They also have a model for 110-220 volt AC so no power supplies required for those.

Nice video made by JazzCNC of how they work
https://www.youtube.com/watch?v=ZMZdCcLQc4M

Company that makes them
http://www.leadshine.com/category.aspx?type=products&category=easy-servo-products (http://www.leadshine.com/category.aspx?type=products&category=easy-servo-products)

I got them but my machine is in the build process so I have no idea how well they will work. I have played with them and its easy to get them running and the configuration software also allows many parameters to be modified if need be.

[vargai]

I got them but my machine is in the build process so I have no idea how well they will work. I have played with them and its easy to get them running and the configuration software also allows many parameters to be modified if need be.

Thanks, just thought there is some DIY made way but it is ok when it is reliable with careful set-up and parameters.
As you said the first to "play" and know the new built machine to find its sweet points.
In this thread and (others) you can find opinion of JAZZCNC of easyservo and he says it works excellent.
Little bit expensive but you have them and you can compare the price.
Could you tell this comparing the same torque stepper pls?

[Boyan Silyavski]

I am planning to attach an easy removable really small, geared spindle driven by the HS one with belt or directly coupled. (EDIT: i see now that the belt not good at this speed) In this method the supposed extension of the original spindle would be only about 60-80 mm and the force not bother the main spindle bearings
With 1:0,5 ratio (12000-to 6000 rpm) and quite enough torque I probably can make a typical steel milling with DIA 4-5 mm mill.

Belts are not a problem here. HTD belts are rated for these speeds. Problems are the bearings. Conical roller bearings will not spin so fast. Hence the 6000rpm limit on the spindles they sell. You will have to use angular contact bearings, not roller bearings, so they have to be over sized. Though i am still not sure if they don't use ball bearings on the spindles. You will have to check this and find suitable bearings and i don't see why it will not work. I have thought about that many times, despite what i said before. Plus my gantry on the machine i am building is rock solid. Though you have to have tremendously strong Z, cause 60-80 mm are big difference when we are talking about Z travel. On a router i mean.

One thing to note is that when we say -"this is bad, can not be done, not like that, you need other type of machine" , its not that it will not work. It will work.But not consistently, not for a long time. No perfect finish. Not be able to hold consistently precision. Ruining some element with time , /bearings/, etc. I can drive a city car where 4x4 car goes, but for how long? So actually its not a discouragement, its a reality check. I will be more than happy to see it done. Cause i will do it also.

Why don't you sketch your idea for the spindle and investigate the bearings.


As for the motors you could fit cheap encoder to steppers and then feed the signal to the breakout board/you will need available inputs/ . When out of programmed way, the machine could stop so you don't damage material. I have a plugin on my PC that does exactly that. Though that's not a true closed loop. The closed loop motors will push till all is where is meant to be and stop only if they could not overcome the force. If you decide to go this way, i will send you the plugin. There are cheap normal steppers with integrated encoders. though definetely will be mistake for the sake of encoders to buy some steppers witch are not low inductance.

Just use good PSU, good board and motors and you will not need these. Though closed loop would be nice on a metal working machine.

[Ross77]

What spindle are you planning to use? I know there were a few mentioned but cant see which one you decided on.

The thing to remember with spindle bearings is the amount of pre-load they have which affects the rigidity and speed.

Taper bearings with a heavy preload will be super rigid and cut hard materials but will be limited to a low speed. If your milling steel this is what you need.

Angular contact (AC) bearings are similar and the heavier the preload the more rigid they become. Due to the reduced contact area they have a higher speed capability but lower load bearing capacity than a similar sized taper bearing.

So as most of the high rpm (15-20k) router spindles will be using AC bearings then the rigidity will probably be low. This will be the weak link and no matter how strong the machine is it wont be at its best.

Bottom line is you can have a machine capable of both but realistically you will need two separate spindles.

You could always get high end spindle with hydraulic adjustable preload :0)

I have 75x40 precision AC bearings for mine and should get me up to 12k for HSM with adjustable preload and with oil mist lubrication lol.

[vargai]

What spindle are you planning to use?
2,2 or 3 kW water cooled chines spindle fit to a general router
The secondary small spindle would be a really light loaded ocassionally used one for the special purpose mentioned.
Short video is attached. The door steel sheet is 1,5 or 2 mm. At issue.That is why I do not want to pay too much attention to it but some searching is not a sin. I will show up some details in the answering to Syliavski and waiting for your comments.
By the way do you have something more then Chinese spindle do not you? from low rpm to 12000


https://vimeo.com/117009926

[vargai]

Why don't you sketch your idea for the spindle and investigate the bearings.

Here is some sketch and I am almost sure the for DIY use with a short 5 mm flute cutter this spindle is quite strong enough.
Cutter is clamped by Weldon @6000 it works, lower AC bearings are coupled and after installation it will be preloded
grease lubricant also fine here.
Some safety issue should be considered:
The drive shaft in the ER20 collet should we carefully machined including the pulley to reduce the unbalance.
I would use double key opposite to each other.
Good cover must be done to protect the belt and user.I checked my 170 mm blade Makita plane , it run @15000rpm so you are of course right regarding the belt application. Here ribbed V belt is used so i think 15 mm wide HTD3 is sufficient here.
If you flip the pulley on the mini spindle to the top to skip the belt from the milling area you have to use some adapter plate .
This is not the first thing i make now but probably later Paris is well worth a mass.



http://www.mycncuk.com/attachment.php?attachmentid=14450&stc=1

[Boyan Silyavski]

Some technical info (http://www.skf.com/group/products/bearings-units-housings/ball-bearings/angular-contact-ball-bearings/single-row-angular-contact-ball-bearings/design-of-bearing-arrangements/index.html) and bearing sizes and data (http://www.skf.com/group/products/bearings-units-housings/ball-bearings/angular-contact-ball-bearings/single-row/index.html). There are some force calculators there and so on. May be you know them already but let be here on one place.


Here is the 3kw/3.2-4kw i believe also/ spindle with all sizes if you dont have it at hand. I took them personally :-) .This is the original Guanzhou spindle with the 4 bearings and the black rings. Maybe enough place that the attachment could be clamped directly at the spindle there.

Hope that helps. When i have time will sit also and see if i have some ideas.

http://www.mycncuk.com/attachment.php?attachmentid=14451&stc=1






These are the bearings and dimensions of the BT35 spindles for reference:

http://www.mycncuk.com/attachment.php?attachmentid=14452&stc=1






Here is some belt info. If i read it correctly best would be HTD3- HTD5 belt or GT belt even better . Dont be put off by the lower life the figures show. After all one belt is 1-4 euro only. One thing to note is that wider than necessary is not a good idea.

http://www.mycncuk.com/attachment.php?attachmentid=14453&stc=1



http://www.mycncuk.com/attachment.php?attachmentid=14454&stc=1


http://www.mycncuk.com/attachment.php?attachmentid=14455&stc=1


http://www.mycncuk.com/attachment.php?attachmentid=14456&stc=1
http://www.mycncuk.com/attachment.php?attachmentid=14457&stc=1

[Ross77]

The general arrangement is really good. Back to back AC's and floating end bearing to allow for thermal growth. Are you making this or buying?

My only concern is that by driving it from the bottom you are increasing the distance from the cutter to the bearings and compromising the design. The belt tension will also pull the spindle off center. Can you drop the bearings down in side the pulley?

I'll try to find my old spindle designs and show you what I mean, I have gone over sized on the bearings so the taper of the collet is inside the bearing.

what size bearings are they? For 6000 rpm have you considered roller taper bearings?

This is of course me being super picky, your design will work but just offer suggestion to maybe improve :0)

[vargai]

Here is the 3kw/3.2-4kw i believe also/ spindle with all sizes if you dont have it at hand.
I prefer to download 3D model of all stuff and it is not supplied so thank you this and other information.
I will make my model to go further.

If one use this spindle occasionally only for fine milling in steel(up to 3-4 mm flute small doc) there is no point to make extra attachable spindle except handling the main gently.
When I am right the main DIA of the rotor is 25 mm(suppose the bore of the bearing same) so it has much stronger then my mini spindle with its 15 mm bore bearing. At this case I would not rank the spindle application
based on material but based on load.
There are coated cutter for HSM in steel rated for 7-8k rpm. At this value the torque is about 1/3 of the top ( I will check the curve) so this gives an additional protection for the spindle.

I have an offer for both 2,2 and 3 kW Guanzhou spindle and saw the 2,2 kW is popular among builders.
Does the bigger worth the 200 USD price different on a general router-or the bigger the better?



So actually its not a discouragement, its a reality check. I will be more than happy to see it done. Cause i will do it also.
I am agree with the advice to go step by step. A 700x1000 mm commercial LSM CNC mill has a roomful foot print and it cannot be compressed to my design with impunity.By sitting in front of monitor and doing 3D designs some(me) tend to loose the sense of reality. So I go further with a router and it gives the possibility beside other matl to work with wood that I like too. In the mean time I can check things in the reality. I can reach from A to C through B and maybe it will be shorter way.



If you decide to go this way, i will send you the plugin.
I have to jump in to the electric stuffs first to understand completely this language.
I revert it later, thank you in advance

[vargai]

The general arrangement is really good. Back to back AC's and floating end bearing to allow for thermal growth. Are you making this or buying?

My friend is renting a small shop and generally I got him to machine the part,and I will put them together.
There are a Bridgeport VMC, a Colchester CNC turn and a Hungarian CNC turn. I used to work here but recently after the daily office job I prefer to have a little brake. That is way I would like to have some machines at home where I can work any time that fits to me.
The bearing is 15 mm bore -for an entry level spindle is Ok but any design comes in handy, thanks.

PS: I have adjusted my setting so the vid is already visible at my previous post to you