Ballscrews vs leadscrews for a DIY CNC

I've upgraded my hobby DIY CNC mill to use ballscrews, and haven't looked back.

[@GoPaintman]

Happy to see another video! I watched your series on the mini mill before I bought my first CNC.

[@Jptoutant]

great info, i like your mills setup

[@Dude_Slick]

I used 3/8-8 4 start lead screws for my router build, and I'm quite satisfied. But then I only cutting wood so I don't need a powerhouse of a machine. I run a good size work area at 24"X46" So I'm contemplating adding a second screw to the Y axis, as I am currently running a single center screw.

[@lohikarhu734]

Interesting discussion...I was looking at some rather precise "stages" used in drilling PCBs ( about 400 x 400 mm), and they were driven with ball screws, I think a pair of them, one per side of each axis, with tooth belt drive between them. Motion control is always interesting... Strange that so much in these CNC systems is open loop?

[@ThoCoKhi181]

Noise has decreased. Do you think it comes from upgrading Ballscrews or high speed spindles? Thanks!

[@Taseden]

What precision cast aluminum plate did you end up using? Same size as the 6061 flat bar you initially used? Thanks for the update on your machine. I plan on using 1204s as well.

[@imnoexpertbut]

Yep. I bought from "USA Metal Online" on ebay, and the plates are G.AL C250, which is "Medium Strength Precision Milled Plate, Alloy: EN AW-5083." Machined just fine.

[@3dkiwi920]

What type of coupler did you end up using there? Looks slightly more complex than the spiral specials.

[@imnoexpertbut]

It's called a "diaphragm coupler," you can find them on amazon.

[@markbunyan3078]

Great video, thanks for sharing! I found this while looking to confirm the calculation for Torque, where did you find the calc in the video? It seems to be different to most that I have found which show T= PL/2Pi e, where the calc in the video shows T = PL e / 2Pi. Where should the efficiency be? Thanks!

[@imnoexpertbut]

I took it from this page, where they should both a drive torque and holding torque equation. For driving, a low efficiency should be higher drive torque is required. For holding, it seems like the same relationship should follow: lower efficiency should mean high holding torque. So now that you point it out, I'm also confused. www.nookindustries.com/resources/general-technical-references/ball-screw-design-considerations/

[@markbunyan3078]

Thanks@@imnoexpertbutthat's helped, i had not previously found the two equations together. I ran some numbers through the equations and i think it makes sense - you need more torque to drive the same amount of load as the motor has to overcome the frictional forces of the ballscrew (efficiency), whereas the holding torque is in a static state, resulting in less torque being required, but having said that, why does the efficiency need to be included in the static state?

[@imnoexpertbut]

@@markbunyan3078 OK yeah, your explanation made it click for me. The T in the holding torque equation is the motor torque needed to prevent backdrive, in which case it makes sense that lower efficiency would make the needed holding torque lower, because lower efficiency is mostly due to higher friction.

[@paradiselost9946]

seems legit... noticed that the el-cheapo ballscrews seem to come with the seals/wipers. being metric is the icing on the cake. the lack of wipers, along with the imperial 5TPI of the screws i got with the CNC kit for my little X2 mill? think it was "robson" brand? no end of troubles! stripped them at least 5 times getting chips out... along with the old "forget to throw g21 in code" on every power up... ouch. yeah, one day i might actually finish scraping and get it back together with the new screws sitting on the shelf.. in hindsight, linear rails and build from the ground up would have been a far better approach than convert chinese dovetails to cnc. that has been a journey! might STILL be a better option... even if i just hack the dovetails out altogether! at that point though, the beds still too small... sigh..

[@BruceWSims]

Not altogether sure what problem is being solved here. AFAIK ball-screws originated as a solution to backlash. I'm left to wonder what tolerances you are working at that "backlash" with ball-screws is a problem. Thoughts?

[@imnoexpertbut]

I don't think backlash is the only advantage, but sure, that's an important one. For a hobbyist, the reason to avoid backlash isn't just precision, but rigidity and avoiding vibration. Cutting forces during climb cuts will pull the work piece into the cut and away from one side of the backlash to the other, which, if you couple it with a small DIY machine that's lightweight, is going to spell trouble. You're going to break a lot of endmills, unless you're extremely careful about always taking cuts from specific directions, which isn't too hard on a big manual bridgeport, but becomes very difficult on a small CNC machine.

[@BruceWSims]

@imnoexpertbut Ahhhh....OK...got it. I think I was mistaking what you were identifying as "backlash". My bad. Apologies all the way around. My own work is on a mini-mini-lathe (see: Sherline) so that was my frame of reference. However, if you are talking about a full-size lathe I can definitely that. Sorry for the fuss......