Belt Driving your leadscrews !

Hi,

I'm currently designing a new machine; ideally I want everything kept inside the machine footprint. I have been thinking about using a belt drive system for my X axis, this should enable me to keep the motor from sticking out of the machine like you see on many machines.

What I would like to know is, what are the benefits of using a belt drive system, is there any down falls to using belts, dose using a belt drive system change anything significantly that it needs to be highlighted or mentioned.

I like belts because you can keep the handle on the Y axis, there are no problems aligning shafts, no expensive couplings and with the right reduction you can half step the motors rather than depending on springy microsteps. Bigger motors don't overhang the top of the mill bed, the Z axis motor doesn't shorten the screw travel if the top pulley box overhangs, don't know why anyone would want to do it any other way :beer:

I like them, on my X1 I can just slip the belt off and its back in manual mode, you also get a bit more tourke.

Peter

Horses for courses, belts do have a space saving advantage if tucked away right but it doesn't remove the bulk, only moves it.
Cost wise it's still comparable on the small Nema 23 sizes with Oldham couplings although if you design the Oldham couplings into the drive train you can also get smaller, less looking like Price Charles and also save money in that you only need a torque disk to buy.

This is a Taig mill I converted to CNC about 4/5 years ago using belt drive.

http://www.stevenson-engineers.co.uk/files/taig07.jpg

It was done this way because I didn't want to use the flimsy Taig mounts, it could have been more compact if I had reversed the motors but I wasn't worried about space, just wanted a robust mount. Cons of this setup are you are still reliant on the original bearings for thrust / preload unless you re-design them.

As an aside why when people do direct mount conversions do they hang them out on studs looking like a grandfather clock ? It's got to be the least rigid type of mounting known to man or beast.

Going direct mount if you put a bit of thought into it you can get a quite compact and rigid design.

http://www.stevenson-engineers.co.uk/files/x3xaxis.jpg

This is the X axis off an X3 CNC conversion, Nema 23 motor but it's the longer triple stack motor, note the mounting which is only 60mm deep, this contains two angular contact preloaded bearings and the Oldham coupling.

Everything needed is in this mounting block, very rigid, completely sealed and far more compact that the pillar mounting that everyone seems to choose.

John S.

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mounting block, very rigid, completely sealed: good idea for newbie.

Two words.......

Denford

Boxford


:smile:

Quote:

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Originally Posted by John S

This is the X axis off an X3 CNC conversion, Nema 23 motor but it's the longer triple stack motor, note the mounting which is only 60mm deep, this contains two angular contact preloaded bearings and the Oldham coupling.

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GREAT REPLY! THanks for taking the time to write that + add photos. Really helpful!

When you say Angular Contacts - do you remember the spec + angle? I assume that these are for the leadscrews and the house acts not only as a motor mount + coupling guard but also a leadscrew support block with angular bearings, spacers, etc?

With the couplings ... what method of attach is best ... woodruff, set screw ... etc?
Same if you were to use belts what would you suggest? as it would have to be considered before the ballscrews are turned

hi,

i just looked into using timing belts and pulleys for my x-axis and have decided against it, i too wanted to mount my motor above the x axis instead of having it stick out over the end. They're pretty easy to set up and fairly inexpensive as you've probably seen, but by all acocunts, and this comes from a friend who has built quite a few of them, not the best of choice if you're using a ballscrew as your drive mechanism, since you are going to lose the accuracy gained by having that kind of scew. couplings are probably your best way to go, at least if mega accuracy is what is needed.

saying this though i'd still be tempted to give it a go , being the inquisitive type.. apparently the T5 Polyurethane betls are the way to go, but again who am i to know. good luck. have you made uo your mind yet to go ahead with the conversion?

I run servo's so was pretty well required to use belts. However, a side benefit that has proved useful was when I tried to do a G0 into a hard stop beyond the end of travel for the axis. Instead of breaking something bad, I only lost the belt as it sheared the teeth off of it. A quick call to my local supplier and I was in business the next morning.

after posting what i did, anti pulleys and belts.boo. ive gotten a bit more feedback from people who use them.. apparently the GT2 profiles for belts are good and accurate (actually probably more accurate than using the couplings that i have at least)dont know what your setup is. i might well personally give it a go.. will get back with the results when i do.

I am planning to belt drive my Y-Axis purely because of the space issue. I dont want the motor sticking out that far. I'm not worried about it on the X-Axis though. Hopefully I will get the motor and bearing mount machined today and assembled. I will post some pictures on my build log if I get it done.

Ian