new build opinions required

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-Mesa 7i80+7i76 or 5i25+7i76 . More and more seems Linux is the way. First combo is 119$+150$ +~ 40$ shipping=~250euro , second combo is 200$+~40$shipping =~180 euro.

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Silyavski If you are thinking of Linuxcnc and need to slave motor on one axis there is a problem with homing that has not been ironed out yet. See here LinuxCNC Support Forum :: Topic: Homing and limits with X axis 2 joints (1/2) and here LinuxCNC Support Forum :: Topic: Configurate Slave Axis (1/4) This might be being fixed in the next release. ..Clive

again, a few very important bits of info between you lot there.

I see the sence in the more expensive cards, i will pick one of them. and its seems that there on it with linuxcnc and homing double axis, and there are some work arounds, I like mach3, but hate windows, although i have to use it sometimes, but it is worth using a windows machine just for mach3/4.

I found a local company that can supply me the b-screws and rails and barings ect. and there are a few high precision engineering company's near me as well, so am looking at some alternative mounts for the Y gantry to the x axis. I have been reading with interest on here the posts for R&P over ballscrews. I will put the designs in sketchup in the next day or so.

2 rails per x axis side, one above, one below, 2 barings per rail, seems to make the most sense on an equal loading/force approach. Maybe its not a bad idea to have the barings as the week point, Because they are cheeper to replace in time and money, compared to unbending a machine gantry. If, from the design stage, you consider the barings as consumables ( not to short a life time though ). it free's up some design options.

R&P suits a heavy gantry, and i can see why most heavy machines use it, but, when your building your 80k to 100k + to sell to a customer, the customers not going to acsept thaty every n100 hours of running, they will have to replace the barings, and every n1000 hours , the ballscrews, so you design a machine thats heavy enough to absorb the forces, to give your barings and ballscrews some help. but the extra weight requires bigger motor or servoes, and causes other problems, or pushes you design in certan directions.

wereas, if you specificaly design your machine for the barings to be the week point, you can make you Y gantry a box, that contains a Z Axis, thats a box iteslf with rails on both insides of the Y gantry. The hole Y ganty, clamped by rails and barings on the top and bottom of the X axis, with the ballscrew in the gap between them (between the edge of the Table frame/X axis and the Y ganrty box ).

Done this way, every axis forces are contained within the box frames, and takes out any levers if you get what i mean, all the above gantry designs are big leavers that you have to compensate for. Whereas, if the only leaver is the projection of the bit from the Z bottom, and that is within the X frame box. What this gives you is equal forces/loading in X and Y both directions, and a very strong Z Boxwith heavy down force capability, but, very heavy loading X and Y, if the Z is retracted and only the tip of the bit is projecting, Like for surfacing a large piece of stone.

Also, a box within a box makes sence because you can bolt certan cruital parts inplace ( Y gantry ), on the machine, make sure there all square and level, before you weild, and you can use the bolt points to strengthen up the metal near the weilds, to help ofset any twisting/pulling your frames wants to do while its weilded.

My main reason for designing like this, apart from equal forces in all directions, is machine down time if a mistake is made, This is through experiance of owning/running a Gocarting track 97-2001. Go carts have lots of expencive barings in them, and after 2 years of large parts bills, we redesigned and refitted the frames, to eas of on the barings, What a mistake, we spent a lot less on barings that season but down time per cart frame due to bending was horrendus, each frame had to be stripped and bolted in the jig for 2 days, heated and coolded, then brazzed, then rebuilt, That job went from once after the end of each season, to frames queing up to be placed in the jig.
My point being, make a mistake and bend your machine, your down time is a lot more (maybe days ), and you dont know what the cost of repair might be, whereas, if you pop your barings, its costly, but you know how long it will take and how much it will cost before your machine is running.

I will try get it in sketchup later

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Originally Posted by Clive S

Silyavski If you are thinking of Linuxcnc and need to slave motor on one axis there is a problem with homing that has not been ironed out yet. See here LinuxCNC Support Forum :: Topic: Homing and limits with X axis 2 joints (1/2) and here LinuxCNC Support Forum :: Topic: Configurate Slave Axis (1/4) This might be being fixed in the next release. ..Clive

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Thanks for the info. Though here is what i think of it in my case, may be concerning this build also:
-if the machine is rigid like mine and like this will be , may be it shouldn't be a problem. With Hiwin 20 HA bearing spacement at the gantry sides of 40cm/ or even 30/ i don't see how it would go out of true, its not a flimsy machine we are talking about here.
-i would use servos, they will simply stop due to error

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Originally Posted by george uk

again, a few very important bits of info between you lot there.


2 rails per x axis side, one above, one below, 2 barings per rail, seems to make the most sense on an equal loading/force approach. Maybe its not a bad idea to have the barings as the week point, Because they are cheeper to replace in time and money, compared to unbending a machine gantry. If, from the design stage, you consider the barings as consumables ( not to short a life time though ). it free's up some design options.

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I still don't like that design of yours, but that shouldn't discourage you :-)

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Originally Posted by george uk

R&P suits a heavy gantry, and i can see why most heavy machines use it, but, when your building your 80k to 100k + to sell to a customer, the customers not going to acsept thaty every n100 hours of running, they will have to replace the barings, and every n1000 hours , the ballscrews, so you design a machine thats heavy enough to absorb the forces, to give your barings and ballscrews some help. but the extra weight requires bigger motor or servoes, and causes other problems, or pushes you design in certan directions.

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I don't know if i am understanding you wrong. But:
RP is far more wear prone than ball screw. Ball screw is far more better and smooth. for 6m long table, yes RP, but for anything under 3m-ballscrew.

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Originally Posted by george uk

wereas, if you specificaly design your machine for the barings to be the week point, you can make you Y gantry a box, that contains a Z Axis, thats a box iteslf with rails on both insides of the Y gantry. The hole Y ganty, clamped by rails and barings on the top and bottom of the X axis, with the ballscrew in the gap between them (between the edge of the Table frame/X axis and the Y ganrty box ).

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IMHO the weakest points in order of a DIY machine FYI:
1. Router bit - deflection
2. Z overhang-plate twist
3. Gantry twist and bend ,
4. Gantry sides
5. bearings/assuming you use square
6.Spindle power
7. Balscrew support bearings, spindle bearings
8...etc

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Originally Posted by george uk

My main reason for designing like this, apart from equal forces in all directions, is machine down time if a mistake is made, This is through experiance of owning/running a Gocarting track 97-2001. Go carts have lots of expencive barings in them, and after 2 years of large parts bills, we redesigned and refitted the frames, to eas of on the barings, What a mistake, we spent a lot less on barings that season but down time per cart frame due to bending was horrendus, each frame had to be stripped and bolted in the jig for 2 days, heated and coolded, then brazzed, then rebuilt, That job went from once after the end of each season, to frames queing up to be placed in the jig.
My point being, make a mistake and bend your machine, your down time is a lot more (maybe days ), and you dont know what the cost of repair might be, whereas, if you pop your barings, its costly, but you know how long it will take and how much it will cost before your machine is running.

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You can not bend with steppers a properly constructed machine. They will simply stall. Remember this. Nor you can wear Hiwin bearings if properly mounted. When you have them in your hands you will see why. They will be probably that last element in a machine to fail.

Back to the BOBs

I have another questions in mind concerning the BOBs. Please some one more knowledgeable clear it for me:

-With steppers: If Mach 3 outputs as max 100kHz pulse/ even less normally/, then a normal reliable board that supports 100khz should be ok, yes?

-With servos: If Mach 3 outputs as max 100kHz pulse/ even less normally/, then why should i care to buy a board like the CSMIO or other? I know, apart from the reliability and connections, i mean. Every modern servo drive can upscale by gearing the frequency and generate the proper signal , so why waste money on expensive cards that will do exactly the same thing in fact? I start to believe that the driver generating the pulses will be quite better and reliable..
It seems that mach3 is the limiting factor, not the board?

Hi

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Though here is what i think of it in my case, may be concerning this build also:

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i agree with what your saying here, am thinking i may cog and belt the 2 ballscrews together, to stop any small chance of them going out of alignment. Or, go back to using one motor to drive both ballscrews.

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I still don't like that design of yours, but that shouldn't discourage you :-)

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Dont worry me, i prefare people to be direct and to the point. and getting something wrong is not failing, its a leaning step on the way to success.

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I don't know if i am understanding you wrong. But:RP is far more wear prone than ball screw.

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I was thinking aloud, i am going with ballscrew,

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You can not bend with steppers a properly constructed machine.

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I have seen this happen, Nema23 on z, Z bocx mounted forward like you pictured. Z down gave it enough leaver, that when his limit switch failed, put a slight bend in a very well constructed Y gantry, both the mounting rails and ballscrew had a noticable movment when passing the point were it had bent.

He was very ham fisted with his limit switches, hence it failed, but it did bend it, i will have a go at doing the math tonight again,

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IMHO the weakest points in order of a DIY machine FYI:
1. Router bit - deflection
2. Z overhang-plate twist
3. Gantry twist and bend ,
4. Gantry sides
5. bearings/assuming you use square
6.Spindle power
7. Balscrew support bearings, spindle bearings
8...etc

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Wen i consider the list of week points, i think of it more the order i would want it to break if it does go wrong. I need to put my design is sketchup so you can see it,

am thinking ( but will acsept that am wrong, ), is that No 1 should be the baring mount screws or the baring, I think you will understand when you see my X design.

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Originally Posted by george uk

Hi



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I have seen this happen, Nema23 on z, Z bocx mounted forward like you pictured. Z down gave it enough leaver, that when his limit switch failed, put a slight bend in a very well constructed Y gantry, both the mounting rails and ballscrew had a noticable movment when passing the point were it had bent.

He was very ham fisted with his limit switches, hence it failed, but it did bend it, i will have a go at doing the math tonight again,

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Thats why i insist that only 2 possible models of homing and limit switches should exist, no other variation trade-offs, like the ones popularized by Mach3 in fact:

1. Small hobby machines with weak motors and more or less rigid / like mine current one/ - no limit switches, instead software limits . Mistake, axis go to end , motor stalls and nothing happens. Probably limits only on Z, as there could be a problem with flimsier ones/ like mine :-)/ Its typical situation where the BOB has limited I/O.

2.BOB with a lot of I/O and homing and limit on for each axis on SEPARATE I/O, so a limit switch is a limit switch, nothing else. Thats what i intend to do and advice you for your build, this with my limited knowledge. And if servos, the limit switches directly to the servos, not the BOB, i don't see a reason why the servo should wait for the BOB to tell him to stop. Cause with servo, a lot could happen in a very short time if geared and running fast. It seems most of the servos i looked at support it, so they stop and later they tell the BOB that they are not moving .

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Originally Posted by silyavski

-With servos: If Mach 3 outputs as max 100kHz pulse/ even less normally/, then why should i care to buy a board like the CSMIO or other? I know, apart from the reliability and connections, i mean. Every modern servo drive can upscale by gearing the frequency and generate the proper signal , so why waste money on expensive cards that will do exactly the same thing in fact? I start to believe that the driver generating the pulses will be quite better and reliable..
It seems that mach3 is the limiting factor, not the board?

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Mach3 is only the limiting factor when using the parallel port and even then it's Not really Mach3 it's the Parallel port and it's driver.
When you use an external motion control card all these restrictions are taken away and infact Mach3 does very little other than watch I/O's and this is why low spec PC and Laptops can be used.

Now with servo's the freqency rate becomes important because the encoders and depending on the encoder count will depend on if you need higher than 100Khz. Which for most servos you will with out using the electronic gearing feature built into the drives.
Most who are using servos avoid electronic gearing because it lowers resolution and often the whole point of servo's and encoders is to give high resolution.

Now lets say you are using typical servo's with quadrature encoders having 2500cpr this means you need 10,000 pulses per rev so divideing the controler Pulse rate (IE: KHZ) by this amount gives Pulses per sec then times x 60 will determine the maximum speed you'll get from the Servo's. . .IE: 100Khz / 10,000ppr=10pps x 60s=600RPM

So has you can see 100Khz won't be much good if have 3000rpm servos has the fastest speed you'll get is 600rpm.!!

Now if the drives have electronic gearing multiplier then you can use this at the expense of resolution. So when 4x multiplier is applied then for every 1 pulse Mach3 controller sends out the drive will see it has 4 so 100Khz becomes 400Khz but the resolution is divided by 4.!!
400khz/10,000x60=2400Rpm better but still not enough so you'll need to use the nearest or above to give the 500Khz you'll need for 3000rpm with 2500CPR encoders.!!
Electronic gearing can be ok for some machines because the resolution will be very high to start with.!!

The next problem comes from the BOBs if used and it's Max pulse rate causing a bottle neck and yep most typical BOB's don't go that high so you'll need a very fast BOB and high quality BOB if your using servos with high pulse counts.
This is also why lots of High end motion control cards don't use BOB's so to speak (IE Csmio) and connect direct to any devices attached or thru dedicated daughter boards which don't cause a bottle neck.!

So be warned to all those dreaming of using servo's just be aware they take you to another all new level of head scratching and expense.!! . . . . . So I honestly suggest you ask your self do you Really Really Really need Servo's.??? . . . . . . . Oh and just be aware they are still not closed Loop with Mach3.!! . . . . . The best they can do is Fault if they see a following error.

For 99.9% of DIY machines and even relatively slower Light industrial machines steppers if spec'd and setup correctly are far far far less hassle and plenty accurate enough.

Dean,

thanks for the great input, cleared some clouds :-) , but still my question stands:

Mach3 outputs normally 25khz pulse. On a perfect PC it could output stable 100kHz /or even up to 300kHz before it locks, on a top computer, according to its creators/ .

Now, how these 100kz become 1Mhz or 4Mhz on CSMIO, Galil or whatsoever when mach3 outputs only pulses, not trajectory information. They generate them, the same way a geared servo drive generates them, so in fact - no real resolution benefit at all with expensive boards for the $$$, coupled with servos, steppers and Mach3. Apart from the reliability , ethernet or usb connection and I/O. It seems to me that these Mhz they are offering are a hype. No body can prove to me that a generated signal from a BOB is better from the same signal generated from a Panasonic servo drive electronically geared, for example.

Dont ask me who put this in my head :-) but now i have it clear after that digging, it took me a week to wake up from the hype- until Mach3 or 4 or.. closes the loop at the PC and transmits trajectory signal to the motion control, i wouldn't care for the Mhz of the boards. It wouldnt happen on windows, except on some kind of dedicated hardware pc probably.

That investigation answered the other questions of mine, why the good DSP motion control cards have + encoder inputs, / not only for Analog servo drives i mean/ . And why a separate dedicated motion control solution for a machine is so darn expensive.

Now seems Linux a kind of do that what we are speaking of. Wow, i am starting to defend Linux :hysterical:

No you miss understand. Mach is only limited and prone to crashing when using the Parallel port at high Khz ratings.
The Parallel port and it's driver are the problem when using high Khz and struggle above 60Khz.

Motion control cards free Mach of these problems and it's Now the job of the Hardware on the Motion control card to generate the pulses NOT Mach3.
Mach3 just passes the trajectory Data to the Motion control which Buffers it in memory then generates the pulses needed, which it can do at very high pulse rates.

The main differance between Mach3 and Linux Cnc is that Mach3 and it's Motion control cards have to buffer information and Linux works in real time.
Can't speak for Linux has I don't use it but I can for MAch3 and it's motion control cards and trust me it's not hype. They do exactly what they say and generate very clean high quality pulses very fast.!!. . . . . If they didn't there would be lots of very very unhappy people who are now daily running industrial machines for there living which have been converted to Mach and using high count Servo's with encoders.!!

Also not sure what your on about regards Bob and Servo drives.? . . . . Bob does nothing more than distribute signals and servo drive does nothing but receive signals. Again I think you confused here.??

Ok,
May be i am mistaken in my limited understanding. Will stop here. Still not knowledgeable enough. Will have to investigate further. It still though is quite mystery to me how Mach3 passes trajectory data if it sends only pulses, meaning the card doesn't know whats next or what to expect. May be it has to do something with the drivers/plugins for each card and mach3.

No problems with the BOBs :-) , just want to make sure they do all what they claim to do and don't mislead us in some subtle way. Want to be a wise buyer and make sure where my $ could do a better job.

Mach doesn't send Pulses it sends "DATA". . .Has in Trajectory DATA to the Motion control Card which use's this DATA and does some Complex Maths with it to then create "PULSES" which it outputs to the drives at very high speed and with nice clear crisp signal. Whether that be Stepper or Servo drives or any device that expects Pulse signals.

Now if you want Closed Loop with Mach3 then you can have it.? . . . . But Mach can't do it internally, the Motion control card has to do it and there are very few that do and these come at a cost.

Electronic gearing in Servo drives are just Multipliers, they can only multiply what comes in and essentialy this comes from the encoder. So to give an overly simplified example say the lowest resolution your encoder can read equals 1mm and you have 4:1 gearing in the Drive then your lowest count or best resolution encoder can read now = 4mm. . . . So your speed increases but your resolution drops.!! . . . . . . Just has in life Everything that's free cost's something.!!

Again, very usfull stuff in there.

Am using motors as i can easly get the resloution i need and if i make a mistake i can change them reletivly cheeply,

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Nor you can wear Hiwin bearings if properly mounted. When you have them in your hands you will see why. They will be probably that last element in a machine to fail.

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You not considering the difference in wear when using stone, Its not just the heavy use on the machine parts, your basicaly air-rating grinding paste. allthough the powder feels fine and soft, on a particulate level, its rock hard and sharpe. vacuums and covers can pre-long bearing wear, but, you are going to wear rails and bearings when cutting or surfacing stone. Then think that large beds are hardly every fully utilised, everybody's got there own favourite sweet spot on there machine were most of the smaller jobs get done, so you get uneaven wear.

If you then want to surface a large bit of stone, 1500mm by 800mm, you would see the wear patterns in the surfacing as the rails and screws go between the commonly used area and the less used area.

There are other considerations as to why it might be a good idea to have the bearings as the failure points. Re=straightening a frame, or gantry, is quite a long and complex job, that involves building a jig, usualy into a thick concrete floor, and gooing through a heating,cooling and tighnening routines, then when its in shape, heat it and cool it to even the stresses.

8/10 times, it would be cheaper to just remake the gantry, and salvage the unbent parts.

whereas, if you specifically design your frame for the bearing to be the week point, servicing is easier, serviced periods are calculable and variable depending on machine use. and as long as your bearings will fail, beyond the maximum cutting forces your machine will exert, then you could consider it a safety feature.

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Originally Posted by george uk

whereas, if you specifically design your frame for the bearing to be the week point, servicing is easier, serviced periods are calculable and variable depending on machine use. and as long as your bearings will fail, beyond the maximum cutting forces your machine will exert, then you could consider it a safety feature.

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Your correct about stone being grinding paste but don't agree that you will be designing in the rails to be a fail point.?. . . . They will naturaly be a fail point because they are moving components, has will the be ballscrews and nut.
So instead of designing in what will happen anyway put all your design efforts into the best way to limit or avoid this.

Best why I know off is to cover and conseal so get them either up high out the way or under neith and under cover.!! . . . . Now Remember you'll be using Mass's of water which tends to run down hill, also gravity brings droplets down eventually so personally I'd be looking to get the rails higher rather than lower and still under cover has much possible.

Then you have the Ballscrew or R&P debate.? At 3mtr length then the Only way I'd use ballscrews is if they used rotating ballnuts. Which would actually help with reducing the number of rotating parts and be much easier to cover and conseal.
To use rotating ballscrews at 3mtr length would require at least 25mm Dia screws which then takes you into large Stepper motors/ drives etc added to this the fact your gantry will be heavy anyway means even larger motors or going with servo motors and all that comes with them.!
This is why ballscrews and long machines don't match perfectly well and if you find any long machine that use's Ballscrews you'll see they often have large diameter screws with a Large pitch thats geared with ratio to keep the rotation speed down and whip from happening. They also have servos on the ends because steppers can't handle the torque required to Accel and Slow from traveling a heavy gantry with large rotating mass.!

R&P is there foreoften used when accurecy isn't the prime concern because it's less expensive and has less rotating Mass. Down side is it's less efficeint and more exposed and prone to interference from debris getting into the workings so again needs careful placement and consealment.!!

Which I'd use would depend on machine design and my budget.? Probably Ballscrew because I prefer them but 100% it would be a rotating nut and up high out the way along with the rails. This is where all my design efforts would be concentrated and even if it cost extra money to put up high and under cover because of building in the extra strength required I would do it to save on the down time which would come from replacing worn components.

Machine setup can take many hours or days and even weeks at DIY level if your after close tolerances so anything to reduce this or limit having to disturb the finely setup machine would be my prime concern along with strength and accuracy.

Now I'm going to honest and blunt here George.!! . . . . I think you are going to waste an awful lot of time and money plus dissapointed with results because what your wanting to have is Large machine that is all things to all materials but haven't got a clue to just how hard that is to achive or make happen.
When you go large even with machine designed just for one main purpose the design and build process takes you to new levels, expensive levels well above the average DIY build. SO to try and build a machine to be ALL THINGS to ALL MATERAILS with advanced features like 4th & 5th axis etc is a BIG BIG BIG under taking that would make even the most experienced DIY builder like Jonathan or Me sit down and think very very very carefully.? . . . . . To take a project like this on with NO experience is a recipey for wasting money and time .!
My advice is don't do it and build smaller or focus at one machine designed for that main task, which at this size will still be a very very big challenge for some new.!!

Hi

I have reduced the length of the macheen to give me just under 2000mm cutting in X. I have really took a lot in that has been discussed on here,

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SO to try and build a machine to be ALL THINGS to ALL MATERAILS with advanced features like 4th & 5th axis etc is a BIG BIG BIG under taking that would make even the most experienced DIY builder like Jonathan or Me sit down and think very very very carefully.? . . . . . To take a project like this on with NO experience is a recipey for wasting money and time .!

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Its not beyond my current skill set, althoug i have not built a CNC router before, i have had experience in pulling some quite complex tasks together, and i live in an area, full of engineering works, anything beyond of my level of accuracy, can be done by them. I do understand that it will cost a lot, perhaps around the 5k mark, without software. and i have a few month to do it, with the funds currently sat in the bank,

I will try hard to put it in sketchup tonight

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Now I'm going to honest and blunt here George.!!

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, your not blunt, your straight to the point, and sharing your considerable experience.

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I think you are going to waste an awful lot of time and money plus dissapointed with results because what your wanting to have is Large machine that is all things to all materials but haven't got a clue to just how hard that is to achive or make happen.

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I do understand the difficulty involved, and the design complexitys, am not expecting to get thinks perfect first time, and i have budgeted some funds for mistakes.

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it would be a rotating nut and up high out the way along with the rails. This is where all my design efforts would be concentrated and even if it cost extra money to put up high and under cover

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agreed, my x-rails and screw, are the top of the frame/x Box, The Y/Z is underneath that. I would cover X with accordian or brushes for dust.

Hi

Can anyone see any problems or design issues with this described below.

Standard re-enforced rectangle box frame made out of 80mm 80mm by 4 mill ( or 100omm ) 2200mm

On top of that, down the X, Two bits of 160mm by 80mm, fixed, bolted to frame. I beleive i can get these true and level, ( with machineing and epox ). I then want to bolt rails ( round or square ) to the top and underneath of the overhang, both sides. Apart from the difficulty of getting the rails level to each other and true

What other problems can anyone envisage. ?

It would seem a very obvious design to give you close to equal forces in most directions but i can not see any machines designed the same way. The problems i have envisiaged

Trueing and leveling for the Rails. ------- think i have that covered
Deflection forces on overhang ------ Theses exceed the possible forces applied by the Z, so not a problem
Nobody else usese this design -------- This is my biggest problem , there are a lot of clever people on here, noboby seems to do it this way -- why.

Fire way with opinions , Am especially interested in anyone that has previously considered and discounted this.

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Originally Posted by george uk

Hi

Nobody else uses this design -------- This is my biggest problem , there are a lot of clever people on here, noboby seems to do it this way -- why.

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There is a reason skydivers pack 2 parachutes :whistle:

Just joking, couldnt help . Lets see the design when you draw it

Hello George well intrested as You are building a machine for similar reasons,,
I Spent a couple of years building sound rooms for recording studios (in my spare time)You tend to find out what dampens vibration, Which is Dry sand filled tubes and walling .if the sand gets wet then it doesn't help at all.
Guts on masonry always under the table with a Drip check and should be dry when you look under when the machine is in full spray.

the overhead type even when the Gantry is 600 higher than the workpiece still gets covered in Abrasive dust and the rails wear quite quickly.
Ive seen at least 3 machines fail because of rails being on top or the side.
Humphries Masonry in Hungerford their machine right before xmas rails scored by a pieces of stone about the size of grass seed and all the carriages and rails needed replaced. Blooming expensive 3 metre Kolb machine

I had a look at a machine which uses 120x60x3mm 2400 on x and 1200mm on Y
this machine also had Hexagonal rails and v rollers on the X with 45degree 45mm v rollers on the Y and Z. I cant find Hex rails on the net it all seems to be profile which Jazz suggest.

Hi Ramsbury

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Guts on masonry always under the table with a Drip check and should be dry when you look under when the machine is in full spray.

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I noticed that on the ones i looked at, am trying to avoid it, becuse of the rebuild time required if they do fail, Knowing that the rails and baering will fail, i want them accssesable without heavy lifting.

I think the V barings and design styles on stone machines are to do with the machine weight, and i think , with the right design, you can reduce the required weight substantialy, making everything else easyer to make.

With top mounted V Baerings, you need a considerable weight gantry, just to hold it on the rack. and there starts you chicken and egg game with motor sizes and rails.

Wereas, i am considering, bolting on a lenght of 160*50 by 3mm , down the X, and mounting rails both on the top and underneith, using the shearing/form strengh of the baerings and rails to act like a counter weight when the Z is pushing down. Allowing the gantry to be considerably lighter, and easy to design.

Am going a lillte under 2200mm on the X, becuase i think i need to maintain a relationship between the size of X, and the gap between to baerings on the Y width per side, to small a gap will allow to much resonence down the rails, With the Y Lenght at 1200mm, i think i need the Y width someware between 300mm and 400mm, That meens if i want a X cutting area of 2000mm i need an overhang of 200mm on each end of the X ( making the X approx 2500mm in lenght. Am working on the principal that the Y width needs to be at least 1/8th of the X lenght to counter resonance down the X Rails,

I think ( scratching my head ) that the math works out, to give the Gantry enough force to not deflect under the chip loading of the cutter, pushing through stone.

Do you get what i mean ?

I was also thinking of fixing accordion cover to the X and Y if possible, to help counter dust

All the machines I have for cutting stone have hex bar and rollers. which are on top rails and of course have easy access But the table is also on large V rails to load the stone one of them is worn so I don't get the Accuracy I need to Make stone profiles But its still great for straight cuts and 90 degrees . it only takes 15 mins to change the rails except on the Bottom as the rolling table weighs a ton.
all the Hex rail machines with rails underneath do have difficulty changing and the gantry must be Supported when they are lifted off. But my attitude is if it needs changed Its done its work about 4 hours per rail to change only because they are bolted with Sunken heads. even mild steel rails last a lot of cuts and justifys the rail change

Hi again ramsbury.

This is stone machine specific,

am thinking of adding rollers just beyond the start and end of the bed ( X ) and supports, to keep the machine size down. and allow me to do very big pieces.

A column for example, or the upright part of a norman church door, or a church window upright

If i have rollers at the end, and a support trolly, i can machine 2000mm per time, then just move the piece up the table and machine the remainder. If i can design this part correctly, i may even reduce the lenght of the bed. You can use a probe routine to make sure the piece is positioned carfully

Also, am trying to decide between building rollers into the bed, that are jackable, or, an air table, to allow me to position heavy pieces of stone and move it around.

I prefer an Overhead jib or gantry crane they are very easy to make
and move.
the Machine I wish to make has only its Gantry above its working table making things easier to put on and More important Taking off without damaging using either clamps or Vacuum lift regarding heavy objects , straight onto a waiting vehicle or storage area.
I don't do granite worktops and all the gravestones I do are Hand cut and hand finished.
Raised side rails prohibit the full use of the table, as most lifting equipment needs its own space usually 100mm margin area.

another question.

Bolting a frame together, prior to weilding or bolting instead of wielding

Am thinking that i could probably make a JIG for the bolt holes, and am confident that i could make the machine straight and true with bolts. and then just tac it were required, once nearly assembled.

I have been mainly thinking this because my X will have an overhang, were the rails will be placed. and am thinking that, at least that bit, will be easyer to get exactly level, by bolting and shimming first.

Again, nobody seem to do this, and it seams a no brainer as an easy way to ensure a straight and level machine, but, its probably me not engaging my brain, am open to any opinions on this,

People do use that method, such as my build here;
http://www.mycncuk.com/forums/gantry...html#post50664

which actually turned out like this;
http://www.mycncuk.com/forums/gantry...html#post52425

Jazzcnc also uploaded some photos once showing a part bolted, part welded frame. I would think that if it's a large and heavy machine it's a good idea to make sides and ends then bolt these sub frames together.
Regarding shimming, there are two lines of thought. The first as you say, and the method I'll be using, is to bolt the top beam that supports the rails, this way it can be shimmed level. Also within this method are two ideas that I've seen mentioned, one is to use standard metal shims, the other Jazzcnc method is to use epoxy putty where the rails are bolted down until level thus squeezing the putty until it sets. A piece of cling film or similar is stretched over one component to prevent the putty sticking it all together.
The other way is to fully weld the frame and use the 'epoxy method' to level the top prior to fixing the rails, you can search the forum for that.
My own take on it is this; if accuracy is your main concern and as such you will likely be cutting metal to high tolerance, then the epoxy method is best. If you are cutting mainly wood and your tolerances are not so high then the shimming method would most likely work, after all the wood will shrink and expand probably beyond a fine tolerance.

Eddy is quite correct and most of the larger machines I've built have been welded and bolted. It just makes good sense when you think about.!!
Also I've said this many many times.!! . . The more adjustabilty you build into a DIY machine the easier it will be to set it up. Bolting makes for another area where you can tweak a machine into alignment etc.

I also mostly Agree with Eddy's take on it except that full epoxy is better for high tolerances than Shimming because it's not really, it's just easier(Quicker). I'd actually go has far to say it's potentially less accurate because your soley relying on the epoxy with no room for error or improvement where has with shimming you can tweak out any error it just takes a lot of time. Personaly I'd do a mixture of both on a large or long machine that requires higher accuracy.!!

I believe there must be available movement to Get the Highest precision as possible. especially on the rails. so have a preference to Shims.

Shim steel is more expensive that I thought, do people just cut up food/drink cans or is there somewhere to buy an assortment cheap ?

both have advantages and disadvantages.

Epoxy makes sence if your floor is level and machine is square=ish, to take out imperfections,

Shims give you a very high level of presision, but take time to get right

but , then i start thinking back to the days i had a go-cart circuit, and the jigs we built for straightening the frames, we could easly achive very high levels of precision, at complex angles, much more than you would need for rails.

So am thinking why not build a simple jig, into the top of the frame, both sides down the X ( 80mm or 100mm box ). a simple bolt pattern jig, Fix a bit of say 80-160-4, on that just leaving enough overhang to fit rails to, use the jig to get the 80-160 perfect, with a laser level and a few mirriors, you could get a very long X, very accurate, and make sure the opposite x was perfectly alligned.

I do get that this would be a waste for any machine with less then 1600mm X, but, you could be close to unlimited on X length andd get very accurate, with just a very basic tool kit.

My proposed build plan goes like this.

wield

Build 2 ends in Jig ( Y ) 1400mm
Build 2 sides in jig, ( X ) 2500mm , with Jig/bolt patterns

Assmeble square, by bolting together

Fit the 80-160 to the X, by adjusting down on the bolt/jig, to get it perfect as possible, using simple laser.

Then, bolt a bed, on, using you X to ensure your fitting the bed as close to perfectrly level with the x.

further reasons for the above build plan.

1. can be manufactured and assembled at differnt places
2. Easier to get into workshop/transport
3. Final truing is simple, a few spanners, a few cups of tea, and a bit of time.
4. it can be moved, if required, and is simple to true up again
5. It can be built very accurately with simple tools ( pillar drill, cutters and grinders and weilder ),
6. it will be a lot easyer to get a large but solid bed level to the x/y, possibly even have a replacable bed for different configurations,

Cons

1, it uses a lot more steel, but if you want you bed to hold a lot of weight, its not a loss
2. It takes time to make sure all your cut pieces are exactly teh right size, and to get your bolt patters accurate, but, accurate pattens could be printed from a standerd desktop printer, and overlaid,

i can not think of many more cons,

you will notice that i have not mentioned the gantry yet, its because am working on a very differnt type of design, but i need the frame built, to make the final tweeks, my Y is going to be more like a cartridge than a carriage. giving me much better force resitance in all dirrections. Again, for standard XYZ, this may seem overkill, but, if i want to build a turret on one of the Y sides, or strap a B/C head to the Z, then it makes sense, .

any opinions welcome

Quote:

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Originally Posted by JAZZCNC

I'd actually go has far to say it's potentially less accurate because your soley relying on the epoxy with no room for error or improvement where has with shimming you can tweak out any error it just takes a lot of time.

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The problem with shimming is you can't compensate for rail twist with it. I discussed it at length in the recent build log. I didn't include the readings from the shimmed rail in that post, however if you want I can dig out the graphs obtained when the rail was shimmed and you'll see the error was still far worse than the final result obtained using self-levelling epoxy. I'll quote myself, from the build log:

Quote:

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Originally Posted by Jonathan

At this stage it is interesting to note that the bearings slide smoothly on the rails, so although compensating for the height error with shims or a machined profile is sufficient for the bearings to run smoothly, this does not by any means assure accuracy since neither method compensates for the angular error.

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It all depends on how accurate you want the machine to be and its intended use. The error at the tool introduced due to rail twist will be exceptionally small, so you'd need a very strong machine to notice it. The additional wear on the bearings caused by the rail twist will depend on the stiffness and accuracy of the structure they're mounted to, so it's hard to judge, but in a DIY CNC situation is unlikely to be too significant. I'd still choose epoxy though as it's so much quicker and easier than messing about with shims and enables one to get very good accuracy with less measuring equipment.

hi

Quote:

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I'd still choose epoxy though as it's so much quicker and easier than messing about with shims

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,

yes i am doing, i think you did post the readings from your shims then your epoxy, iether that or it was the bare metal and the epoxy.

I was thinking, epoxy on top to take out surface imperfections, ( although a real lot of that would be taken out by the bolt jig ). Am also haveing quite a wide ( down the X ) gantry ( sacrificing cutting area ), so alot of minor imperfections will taken out becasue of the space between the Y barings to the X

Quote:

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Originally Posted by EddyCurrent

Shim steel is more expensive that I thought, do people just cut up food/drink cans or is there somewhere to buy an assortment cheap ?

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Often I use tin foil has it's thin cheap and won't rust.!! If I need more than 2 layers I'm upset.!!

Quote:

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Originally Posted by Jonathan

The problem with shimming is you can't compensate for rail twist with it. I discussed it at length in the recent build log. I didn't include the readings from the shimmed rail in that post, however if you want I can dig out the graphs obtained when the rail was shimmed and you'll see the error was still far worse than the final result obtained using self-levelling epoxy. I'll quote myself, from the build log:

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Why not.? Shimming is all about where you place the shims.! I agree it's not easy in comparison to epoxy but it can be done, I've done it many times.

Your experiences with epoxy are on a short machine but on a longer machine then things are slightly more exagerated and just relying on one method that is fixed or not very flexible is not so clever IMO. That's why I say for a Long machine(requiring higher precision), longer than 4ft I use both methods.!

Why make life hard for the sake of some plates and bolts, which if Epoxy hits the mark first time you don't need to touch, if it doesn't then fine it can still be tweaked if needed. Adjustabilty is Key and the more of it you have without compromising the machines strength the better at DIY level.!!

have had another think, about if i can use the same principals used in making a jig for the top, in the overall machine design and i have had an interesting thought and wander what you think. ?

am using 100mm by 5 at 1200mm high, for 4 main legs at the machine corners. with very accurate bolting patterns pre cut. and patterns drilled for threaded bar. For the lengths (x,y), i was looking 2 lenghs per side of oblong profiles, like 80,160,4mm, cut at 2500mm and 1500mm.

And hers is were the idea come when considering plans for getting the frame as dimentinaly perfect as possible with simple tools. and an easy to build jig/vice.

I can build a simple jig for the bolt patterns, small, and very accurate, Lay out the lengths of 80,160. Accuratly place/fix/drill the jig at set intervals don the X and Y lengths. Doiong it like this, i can initialy ignor any twists in the metal, becuase i only need the 200mm long section were the Jig is to be accurate, so the angle of the bolt holes are perfect ( 5 pattern ). Do this for all the cut lenths and supports, accuratly mesureing were you place the jig..

Lay out the first 2 X sides, on top of 2 lenghts of 100mm/4m at 1200, with the accurate bolt patterns in, Put one bolt in each far corner to get your first square-ish, If any of the other bolt patterns line up perfect, fabulas, but not expected at this stage, Take one of you central struts, put a bolt in the top right, and if you can, bottom left, slight movement of the frame should allow this, Then, use the cheep threaded bar, to do you frame adjustments, dropping bolts in as you work outwards, at this stage, most but not all bolt points will fit.

Do this to both X and Y sides, Dont force ANY of the bolts in, only the ones that fit.

Assmble the sides and cross struts with the same principal, each accurate bolt fitted will pull the hole frame into shape, useing simple threaded bar and nuts to ajust. i should be able to get the frame very close to perfect within reason.

I would be relying on accurate mesurments over small areas, not long lenghts.

I also think there are some other good reasons for this,

1. your using shorter lengths of metal, its easer to pick out or cut reletivly straight lengths, and you still only relying on the small areas of 200mm long being dimentonly accurate, any you could probably pick them out by eye and simple tools.
2. You use the smaller lengths to pull/push the longer lengths into perfect shape, adjusting with threaded bar and nuts.
3. It would make the assembly process at lot easer that wielding, and take out any chance of the wield putting a twist in
4. could be done with pillar drill, £ 40 micro-measure from maplins, basic desk top printer.
all the bolts will only fit when it is,

It will cost a bit in bolts, but, can not see many other problems but can see lots of benefits, like stronger machine, more bolt points, simple

am on with this at the mo.

i think am going with 120 x 60mm 3.6mm with 100mm box for the legs ( 10kg per meter )

anyone suggest a good suppler of bolts,

Quote:

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Originally Posted by george uk

am on with this at the mo.

i think am going with 120 x 60mm 3.6mm with 100mm box for the legs ( 10kg per meter )

anyone suggest a good suppler of bolts,

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My frame legs are 120x60x5 mm got from parker steel they have an online price guide they also do Nuts bolts and tools.
and Devizes steel for odds and sods also do nuts and Bolts.

Special sizes and threads, Nuts and bolts i make myself using my lathe but many times i reckon its easlier Buying them.

Well, all parts cut to length out of 120*60*3.6, will spend some time overt the next few days trying to accurately cut the bolt patterns, prior to assembly

Quote:

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Originally Posted by george uk

Well, all parts cut to length out of 120*60*3.6, will spend some time overt the next few days trying to accurately cut the bolt patterns, prior to assembly

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Sounds like a plan George, have/are you going to start a new build log thread for us to follow or continue here?

.Me

depends on how successful the first attempt works out. i will post the successful result as a individual build log, but

I have a different type of frame assembly planned, hopefully making it easier to assemble a heavy duty frame, relatively accurately. but if it goes wrong, i can disassemble and get it wielded. The idea being make an accurate bolting jig, about 200mm long. a 5 star pattern and a 3 bolt straight line. Start at the center of each length for the first bolt pattern. then accurately measured outwards for the next ones. the advantages being ;
1. your only relying on each 200mm section to be square for you bolt patterns.
2. Your not relying on your cut lengths to be totally square at the end ( perfectly )
3. As you assemble the frame, you will pull out most of the surface twists in the metal, ( as long as you have a proper assembly plan ).

then things am still trying to work out,

1. optimum bolt width/distance between bolt patterns. ( material is approx 10kg pmtr, 120x60x3.6 )
2. No of positions to plan for threaded bar/nuts to assist in initial lining up

Once initially assembled, i can then decide what parts need welding or maybe brazing, and if i have made enough places for triangles in the corners. If done correctly, the final bits bolted on should meen the frame is very close to am accurate box, and very strong. But, if am not accurate enough with the bolt patterns, it will be all over the place.

I will post any mistakes i make on this one, as i go along ( and ask for help ). then post a seporate one for the completed sucsesfull build.
Am currently considering building\buying\converting a mil to get the accurate bolt patterns. as i will need this for the head designs i have in mind. But, ther are a few companys near me that can mill metal to the accuracys i need. So i need to get proper prices first from them.

Dont forget to drill a pin hole near the bolts, at the end i mean. Once assembled and centered and shimmed, you drill and hammer a single pin there at each assembly. That will help eventual disassembly and assembly in the future.