planning on doing away with the belt drive looking into rack gear drive
this is not the one i intend to get but shown to imply what i am talking about.
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Well that’s certainly cool! What benefit are you anticipating? Obviously, you can push harder with the motors without slipping belt teeth…
Accuracy 0 belt issues and i think it will add stiffness also simpler to setup than ball screw. I am also aware i will have to reverse stepper polarity.
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Awesome, keep us updated! I would like to do this as well one day! @DanBrown another benefit I’ve heard this system brings is less backlash as well.
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It should be the opposite. There should be more backlash in a rack and pinion system than in a timing belt system.
Metal gears in the rack and pinion have to have a bit of slop for the teeth to slip over each other. The downside is that if you tighten up the gap, the friction goes up and you have to get more powerful motors. It can get finicky, but you end up getting a much stiffer drivetrain.
Timing belts are designed to have theoretically zero-backlash due to the relative softness of the teeth. They seat into the toothed pulleys tightly, but you sacrifice stiffness from the teeth having some give and the belt stretching a bit.
That said, I’m not certain how much better switching to a rack-pinion system would be, because your weak link is still the stepper motors and how well they hold and push into position. To get rid of that, you’ll need bigger motors and stepper drivers, which overall will cost a lot.
I have recall past users switching from 6mm wide timing belts to 9mm-wide timing belts solve a lot of stretching and stiffness issues. Their aggressive cuts came out much much better. There’s a few forum posts about this on the old ShapeOko2 forums. It’s probably the cheapest way to upgrade the machine IMHO.
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I’ve actually given serious consideration to that, and I will likely change over the first time my belts need replacement. So far, the stock belts have been working great for me, but they are a wear component and will inevitably eventually need renewal. So, I’m just planning to do a swap at that time. All you’d really need would be appropriate end clips, new idlers, and new pulleys…
Thanks for the info! I’m just going off other information someone told me. Your explaination makes sense.
But a rack and pinion system would still be super cool!
If it doesn’t work out for you maybe you can use the rack and pinion for this simple 4th axis upgrade:
http://www.cncsharktalk.com/viewtopic.php?f=12&t=1521
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I don’t even have a clue but i was wondering if the y axis could be locked into place and a quick disconnect plug added to the y axis steppers to divert power to a rotery axis mounted in a cutout in the waste board. just a thought
First if you are going to go to rack and pinion axis drive you need rack and pinions that are designed for that. Second the pinion is not direct drive off the stepper. There is a minimum of a 2 to 1 reduction GT2 belt drive. Third the pinion drive is set up with a spring loaded system that maintains zero back lash between the pinion and rack. Forth you would be better off to move away from the 3 axis standard electronics and software. A system that gives you true 4 axis drivers two of which can be slaved together for the Y axis is best.
You will also have to design new end plates for the gantry that will take your pinion drive system and Y axis rails that will take the rack. The rack and pinions should be hardened and ground. If not they will wear out fairly fast. You also need to keep all chips out of the system.
Is it doable YES will it be cheap NO It is being done on high end CNC router, Plasma cutters and other CNC machines.
Dave
Ariel, WA
The reason for the idea was based off of my friends plasma table that he built. The spring loaded stepper drive set up is fairly simple. as for the rack he has enough to cover what i need for cheap. We have after hours access to his fathers machine shop and a endless supply of scrap aluminum in the .25 inch range in sizes we can use. The rack spares he has are 1018 cold rolled case hardened. In the end if i had to buy everything I would have to say noway. Its just another stepping stone to building my own cnc. But I do appreciate everyone’s input regardless of how hard headed i am.
Shane
Looks like you have done your research. Keep us posted as you do the build.
Dave
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