Rotating Ballnut - design ideas

[wiatroda]

Thanks :) .... mill the pulley teeth on to it.

What belt profile? How wide pulley going to be ? I had to buy 3M HTD pulley recently , but I would give a try to cut my own .

[Jonathan]

I'm using XL belts, purely because I already have lots of XL timing pulleys which will enable me to experiment with the ratios. HTD would be better in theory.

I will use a form tool to cut the pulleys. The profile is a simple trapezium which I have ground on to a piece of HSS. You can make HTD pulleys accurately with a ballnose cutter ... or some people use a drill but I think that's a bit crude.

If you do decide to try it you might find my program here useful:

http://www.mycncuk.com/forums/showth...ating-programs

[Jonathan]

Today I cut the pulley teeth into the first shaft, and whilst that was running made the second shaft.

Pictures:



The belt fits (yay!):



I will cut the pulley teeth into the second shaft tomorrow, then I just need to make the part that connects the shaft to the ballnut, and the ring that pre-loads the bearings...and maybe some bits to act as bearing seals.

[Jonathan]

I have now cut the second pulley, and made the remaining parts for one of the assemblies except the bearing pressure plate. I immediately stuck it in the milling machine vice, put a stepper on and tested it:



Will post a video tomorrow. With me just holding the 2092mm ballscrew in one hand it did 14m/min. Almost certainly more - I didn't try.

Might be while until I finish off the other one since the tip on my parting tool became an Unexpected Flying Object. It might still be ok, but my lathe is buried in so much swarf I can't find it. It took me 5 mins to find the 60mm diameter part I had parted off, let alone a tiny tip...maybe I'll tidy it tomorrow.

[Jonathan]

I've just found this quote from John S. a long time ago:

One area where spinning ball nuts come into their own is on a CNC
lathe. ... a spin off is if you also fit a bevel gear to the nut block you can then drive this with another bevel mounted on a disengageable handwheel. This way you can
get to use a CNC lathe in manual mode without having to rely on
standing at one end turning the ball screw.

(Source: http://groups.yahoo.com/group/CAD_CA.../message/70038)

Backdriving could still be an issue, but you could add some friction to the handle and/or a lock easily enough to combat that. That's tempted me to convert my lathe ... I could probably still use my design for the router, perhaps with better (tapered roller maybe) bearings as the forces are likely to be greater. The tricky bit will be fitting the ballnut into the cross slide.

[boldford]

I've just found this quote from John S. a long time ago:



(Source: http://groups.yahoo.com/group/CAD_CA.../message/70038)

Backdriving could still be an issue, but you could add some friction to the handle and/or a lock easily enough to combat that. That's tempted me to convert my lathe ... I could probably still use my design for the router, perhaps with better (tapered roller maybe) bearings as the forces are likely to be greater. The tricky bit will be fitting the ballnut into the cross slide.

Perhaps interestingly, the George Taylor milling machines used a similar arrangement. The lead-screw being turned by the hand-wheel and the nut being turned by the self-act. http://www.lathes.co.uk/taylormiller/

[Tom J]

I use HTD 5M often and they do not have sharp edges, maybe you should smooth it a bit just to keep belt happy?
Like the concept, did you consider to use RM2010 instead of 2510?
I wonder what to get RM2510 or RM1010, with smaller one bearing choice is better and they are cheaper as they are smaller.
Thanks for sharing Jonathan

[Boyan Silyavski]

The 2788/2720/QCL7C could work i found.

Reference speed 6700 r/min
Limiting speed 10000 r/min


The ball screws and nuts best is to get them from Fred BST Automation, as he has proven himself these years. 3 weeks ago i bought Hiwin from him for 2x 3d printers and he not only gave me the best price around/ i checked just to see the market/ but i had all in 5 days here in Spain.


As far as the HTD5 rounding, Tom, you are right. I assume most of people will cut them on 4rth axis or indexing head. Anyway below pictures of the absolutely correct profile and size of the 30t puley. I have parametric model that have drawn of HTD5 so if sb say wants a 300T pulley up to specs just drop me aline and will send you a DXF. But here i include the DXF for 30T pulley, the passing hole 27mm and shaft 35mm, needed for the important part in the rotating ball nut. So you can base your drawings correctly.

[Clive S]

Boyan the zip file does not work for me. It might be the spaces in it!!

[mekanik]

+1 on that
invalid attachment.
Mike