Rotating ball nut, Ballscrew Pitch, RPM limits, and my particular build pickle

[Bongo]

Hey JazzCNC. That sounds like very good advice. I plunged on and took the nut off!





I actually managed not to lose any ball bearings. Good call on the non-bouncy surface ;)
Didn't have a lot of time today but will make a small vid of the process - once I have successfully put it back together, that is!
Before Taking it off, I could feel with my hand that there was a little side to side play in the nut, though I couldn't detect any axial play that would obviously translate straight into backlash. Anyway, it made me suspect the balls are slightly undersized.

Agree, I probably am better off selling them and going to a higher pitch. What is your experience with cheap Chinese ones vs the branded,JazzCNC? 32mm pitch seems a lot, but I see that it does seem popular to match pitch to dia...

As a side note, the ball diverters are actually metal.
Thanks again for all your thoughts, keep em coming.

[JAZZCNC]

What is your experience with cheap Chinese ones vs the branded,JazzCNC? 32mm pitch seems a lot, but I see that it does seem popular to match pitch to dia...

Depends where you buy from in China.? Chia's ball-screws where you bought those from are far inferior to those Fred at BST sell's.!

Also branded is a loose term because like most things there are good and not so good brands, Then you have to consider that you are actually trying to compare apples with oranges because it's not realistic to expect something that cost's $20 compared to something which costs $200 to be even close to equal.

My experience is that Branded screws are far superior to Chinese screws which is what I would expect given they cost 3 to 4 times the price.
However, my experience also shows me that even for relatively heavy hobby/light industrial use the better Chinese ball-screws are more than good enough for a CNC router provided you accept that they are not going to last forever and at some point, down the round, they will need replacing. But when you consider you could probably buy 4 sets for the price of one single new THK C5 ground screw this isn't such a bad thing for a hobby user or small business who can afford a little downtime.

End of the day you have to be realistic.!

Re the 32mm pitch, with a 3:1 ratio the pitch is equal to 10mm or 16mm with 2:1 however the rotation speed drops from 3000rpm to 1000rpm which is better for the ball-nut.
However, there is a price to pay in that the torque is reduced, but this is offset some by the ratio increasing torque. But for this application lowering the rotational speed is more beneficial than losing a little torque when you have more than enough spare.!

[Bongo]

Thanks for this Jazzcnc, good advice.

The 'quick method' posted above in the youtube vid, didn't really work for me because getting a 2.5m long ballscrew vertical and then being at the top, in a convenient place see clearly into the nuts and spoon the bbs in seemed troublesome...

So yeah, after cleaning everything up with lots of brake cleaner (it was reasonably grubby in there), I used the grease dabs to 'stick' the bbs in place. I'm surprised at how well that worked! :D Did it over a
cardboard box lined with paper towel. Miraculously, number of bbs lost = 0.





Upon reassembly, I realized how poor the 'wiper seals' are. Just pieces of hard white plastic that don't seem to fit very well, and that get slightly deformed by the two grub screws holding them in place. They leave a thick layer of grease from inside the nut, very much ALL over the screw outside the nut, where it will attract dust & debris. Has anyone made their own seals for these ??

Anyway, it's now MUCH less gritty and rolls well. Still has noticeable lateral play mind you... As you say Jazz I think I should cut my losses.
I messaged Fred on Aliexpress. I was considering a double-nut to remove backlash, but looks like he can't do that on 3232 only 3210. Any experience or opinions on using a double nut for such a large x axis? When I asked about c5 screws Fred mentioned 'TBI' ground and TBI C5 Rolled' ballscrws. I'll admit, I have no idea what "TBI" means - anyone?

Ok thanks again guys.

[Voicecoil]

When I asked about c5 screws Fred mentioned 'TBI' ground and TBI C5 Rolled' ballscrws. I'll admit, I have no idea what "TBI" means - anyone?

Ok thanks again guys.

TBI are a Taiwanese manufacturer (Gten are another), from what I've heard they have quite a good reputation, go here:

https://www.tbimotion.com.tw/en/category/index.html

Fred quoted me on some and they seemed to be about 60% more expensive than his normal ones, but it might vary with the type of nut you have.

[JAZZCNC]

I messaged Fred on Aliexpress. I was considering a double-nut to remove backlash, but looks like he can't do that on 3232 only 3210. Any experience or opinions on using a double nut for such a large x axis? When I asked about c5 screws Fred mentioned 'TBI' ground and TBI C5 Rolled' ballscrws. I'll admit, I have no idea what "TBI" means - anyone?

Ok thanks again guys.

Pointless going with double nuts for a router, esp one this size, the material, and the error or flex you'll have in the machine will far outweigh any error you'll see from the nut.
Also, depending on the rotating ball nut design the longer length of the nut could cause issues. Remember you will now be spinning the nut and at high speed, so a longer nut with the flange on the end of the nut will resonate more, the shorter the better really.

This is another reason for using 32m pitch because it's designed for high speed and uses a nut design that suits high speed better by placing the flange in the middle of the nut and recirculating the balls on both sides of the head flange. For a rotating nut, this is very important as it's much better balanced.

TBI is a reasonable quality ball-screw manufacturer and if you can afford the extra they are worth investing in. Ground screws are light years better than rolled but they also come with prices that can be out of this world on the higher grades.