Rotating Ballnut - design ideas

[Lee Roberts]

Feel free to copy or modify the drawings and use them to make your own or get the parts machined by your favorite company... I don't mind.

Thanks for the share JB, ok to put this in the Open Source section?

.Me

[Jonathan]

Thanks for the share JB, ok to put this in the Open Source section?

.Me

Yes if you want I will. I considered posting it there but decided not to as, if I recall correctly, members can't reply to posts in the open source section?

Now wouldn't this exact RM2510 ball nut simplify things and lead to another design, even possibly with 2 of them?

I considered using threaded nuts, but decided not to risk it in this case as I don't know how accurate the thread is. If the thread is slightly wonky/'drunk' or not concentric then that's clearly going to cause a problem that's hard to fix...

[Boyan Silyavski]

Hi Jonathan,
While you are contemplating if you would ever find the time to make me two of these beauties, i am trying to make a detailed drawing in Sketchup which i could share here with your permission.


Would you throw some light on few details please:

-distance from motor shaft center to pulley center? nema 23 yes?
-exact belt length for 30:30 ?
-did you make the 2 holding nuts or buy them?
-thickness of inner and outer race ring of the bearing? It is the 7207 2rs bearing from here yes?

[Jonathan]

Nema 23, 5M HTD belt 340mm long which enables the motor pulley to be anything from 15T to 30T without changing the belt length. Center distance 90-115mm approx.

I bought them - KM5 locknuts:
PACK OF 5 KM Series KM5 Locknut 25mm x 38 mm x 7mm FREE P&P | eBay

That's the correct bearing. You should be able to get the rest from the SKF website. Interestingly the seller specifies that the bearings are 15° or 25° contact angle, but the ones I got have the suffix 'B' which (going by SKF's nomenclature) means they're 40°. Excellent if true...

[Boyan Silyavski]

Jonathan, THANKS!

Great work and info!

As this rotating ball nut idea consumed my weekend and the whole last week, and i am sure much much more of Jonathan's time, here is the Sketchup file for all to use, if this is alright with Jonathan:

• rotating ball nut Jonathan design MYCNCUK.rar

Notes:
1. Every part is labeled , so can easily be found in internet
2. The bearings are recessed 0.5mm in the casing
3. The aluminum is 20mm thick and the bar can be 100x100, 100x90 or as originally 5"
4. Everything is tight fit / I still don't get it how the bearing casings are centered from both sides but hey, i am not a machinist yet :-)/
6. The clearing between the 2510/25.. nut and casing is 1mm
7. The clearing between rotating shaft and the ball screw is 1mm
8. The 2 retaining nuts actually are PACK OF 5 KM Series KM7 Locknut 35mm x 52 mm x 8mm FREE P&P | eBay as the thread will be 35mm
9. There could be small corrections of the lips that hold the outer and inner bearing racing rings, will update if necessary.
10. The motor is from Zapautomation 3Nm SY60STH86-3008B NEMA 23 STEPPER MOTOR, which i assume most will use for this job 8mm shaft

[Jonathan]

2) Optional
3) Note that on the drawing I posted the motor mount is 88mm wide, not 90mm which is the height of the main block. I intentionally left a 1mm gap so that when the block is bolted to a flat surface, you wont end up with the assembly partially resting on the motor mount (if the motor mount isn't attached accurately). The gap is on both sides since I put mounting holes on both sides of one block so they can be mirrored.
4) Very carefully. You use a 4-jaw chuck and a dial indicator.
7) Same, that's fine.
10) Or CNC4you if you want a cheaper option.

Minor point - on your drawing the 6 tapped holes that fasten the ballnut to the mount go all the way through the flange on the shaft. I made them blind holes so if you accidently try to use too long a bolt, the bolt doesn't go all the way through and damage the bearing.

[EddyCurrent]

I know you had the housing made from several pieces originally but they looked a bit complex so is it feasible to make the rectangular housing from 4 or 5 just rectangular pieces bolted together with the motor mounting plate being one side ?

[Jonathan]

Is it feasible to make the rectangular housing from 4 or 5 pieces bolted together with the motor mounting plate being one side ?

That's pretty much how I did it earlier, see posts #50 and #61. One thing to bear in mind is it's harder to maintain the accuracy of the bearing mounts if they're separate parts.

[EddyCurrent]

Damn, the very pages I must has skipped
Yes I realise about alignment, it just seemed easier for someone without a decent machine shop.

[Boyan Silyavski]

3) Note that on the drawing I posted the motor mount is 88mm wide, not 90mm which is the height of the main block. I intentionally left a 1mm gap so that when the block is bolted to a flat surface, you wont end up with the assembly partially resting on the motor mount (if the motor mount isn't attached accurately). The gap is on both sides since I put mounting holes on both sides of one block so they can be mirrored.

I see, will correct it.

There are 2 minor changes from the original design:

- i made the motor mount from the wider side, as many will like maybe 34 nema and it looks more sturdy. I wanted to make a combined nema 23 and 34 mount, but i feel sleepy now. when ready will see if it will stay like this or follow your original design.

-i believe i shortened the rotating shaft by making its wide part go through the motor mount plate. It is now 2mm to place the ball screw nut in its place,10mm for the ball screw nut holding thread, 2mm ring to push only the small bearing ring and 90mm the rest.

I think that all can be further shortened and lightened :
-2mm protruding thread instead of 5mm , when the nuts are tightened
-6mm /shortening the whole assembly/ eating from the clearance near the shaft pulley
-The area where the ball screw nut fastens could be recessed 8mm with diameter 40mm and some more holes could be done / 45 degree following the pattern/

This could lower considerably rotating mass