Accurate Strong Gantry

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Originally Posted by vargai

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.

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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

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Originally Posted by JAZZCNC

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

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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?

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Originally Posted by vargai

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

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

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Originally Posted by silyavski

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?

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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.ph...id=13993&stc=1 http://www.mycncuk.com/attachment.ph...id=13995&stc=1
http://www.mycncuk.com/attachment.ph...id=13994&stc=1

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.

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?

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Originally Posted by silyavski

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

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Originally Posted by vargai

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.

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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.

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Originally Posted by 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. Especially if you are using a heavy moving gantry.

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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.ph...id=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

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.

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.

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Originally Posted by Ross77

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

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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:

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.

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.ph...id=14068&stc=1


Thank you for your comments and advice in advance.

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Originally Posted by vargai

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

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

Attachment 14069

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Originally Posted by EddyCurrent

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

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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

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)

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Originally Posted by Ross77

To get the best rigidity you need to keep the spindle inline with the support bearings so no overhang.

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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.ph...id=14090&stc=1

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.

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Originally Posted by Ross77

Might need to draw something up.

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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.

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Originally Posted by Ross77;

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

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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.ph...id=14142&stc=1
http://www.mycncuk.com/attachment.ph...id=14140&stc=1
http://www.mycncuk.com/attachment.ph...id=14141&stc=1
http://www.mycncuk.com/attachment.ph...id=14143&stc=1

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?

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Originally Posted by 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 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?

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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.

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.!

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Originally Posted by JAZZCNC

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

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Originally Posted by vargai

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

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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.ph...id=14153&stc=1

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.

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

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Originally Posted by silyavski

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.

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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.!!

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)

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Originally Posted by JAZZCNC

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.!!

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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...

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Originally Posted by Ross77

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)

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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

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Originally Posted by JAZZCNC

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.!

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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.

Better read this 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 ?

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Originally Posted by JoeHarris

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.

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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.

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)

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Originally Posted by 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)

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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.

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.

http://aluminium.matter.org.uk/conte...eid=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.

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Originally Posted by 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.

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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.ph...id=14288&stc=1

and the follow is face milling in mild steel

http://www.mycncuk.com/attachment.ph...id=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.

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Originally Posted by silyavski

Its so simple. You want to do all up to aluminum- make a router. You want to do iron, steel and so - make mill.

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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.

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.

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.