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

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Originally Posted by Bongo

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...

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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.!

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.

Attachment 29815

Attachment 29816

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.

Good to see you succeeded!

Can you fit some of those telescopic covers in your machine setup? I bought some from AliExpress recently for my lathe - they are available in a wide range of diameters and lengths. My Shizuoka had them from new and nothing gets close to the ballscrews.
https://www.aliexpress.com/item/2040...41a84c4dNrCmN6

The part numbering system is Dmin-Lmax-Lmin-Dmin where the Dmin and D max are the diameters of the ends of the telescopic springs. Lmax and Lmin are the max and min lengths. For my machine I got a couple of 20-600-40-36 (you need 2 per ballscrew usually).

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Originally Posted by Bongo

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.

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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.

@Muzzer. Thanks, there isn't a lot of room on either side for the telescopic ones, but I'll look and investigate if I can fit them in. My lathe has the same thing over its leadscrew, and I must admit I don't love the noise they make (how yours for sound levels?). Still seems like a simple solution, but I'd still feel more comfortable if the nut's seals were a bit better as well, and maybe had some kind of rubber sweeper... I don't know.

@Voicecoil. Thanks for that, I had a nose around the TBI website you liked to, I guess I'll ask Fred for a quote too. Did you go with his ballscrews in the end? I'm guessing not the TBI ones?

I will do - when I can find some premises large enough to accommodate the machine, but am currently being shafted by COVID, the LDNPA and urban millionaires buying up all the property round here.

Quote:

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Originally Posted by Bongo

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.

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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.

It's been a while, so I thought I'd update. I made a little video on the situation so far https://youtu.be/HF-OtLCGphg
And another vid of the nut cleaning saga to follow…
In other news I ordered a pair of TBI C5 rolled screws 32dia. 20mm pitch from Fred, and they are due to arrive today :D
I will need to do a bit of work on the mounts as the nut is not exactly the same. Then it’s just a question of changing the pulleys and belts…

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Originally Posted by Bongo

I will need to do a bit of work on the mounts as the nut is not exactly the same. Then it’s just a question of changing the pulleys and belts…

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If it's the nut I think then they will be better for you as the flange is more central to the nut body which gives a better balance and less flex at higher speeds. Thou it might mean a re-work of the shaft and flange.?

So here's the ball nut tuning / cleaning experience in video form in case it's helpfull to anyone:

https://youtu.be/vvWdq9KyCvw

The new screws arrived! The nuts are not the ones with the flange in the middle, as that would have required new angular contact bearings, and a whole new bearing block which was more work & expense than I was ready to stomach - maybe the next machine :)