Rotating Ballnut - design ideas

[Jonathan]

Hi Jonathan, any chance you could knock 2 of these units up for me?

Im running the 2020 ballscrew and need someway of using a screw of 3000mm length without whipping and this looks ideal

Yes I can, depending on how soon you need them.

A rotating ballnut would be ideal with the a 2020, 3000mm long screw. Since (I gather) this is a woodworking machine, you would probably want to gear it 2:1 so the gantry moves 10mm for every motor revolution.

Here's one I made recently, version 3 I suppose. The significant change is using sealed angular contact bearings (turns out they do exist) and threading the shaft to enable a pair of locknuts to pre-load the bearings.



Will post a video when I have time.

[D-man]

I would like it to cut Ali is there a reason you think it's just a woodworking machine? What have I done wrong lol?

If you wanted to test the R2020 screw and nut I don't have a problem sending some over as long as you send them back when your done :-)

[JAZZCNC]

If you wanted to test the R2020 screw and nut I don't have a problem sending some over as long as you send them back when your done :-)

Sure he will but in 5yrs time then they'll be bent and worn out. . lol

[boldford]

. . . . .All of those figures are with a 3x safety factor on the torque, . . . . . .

Was the 3x figure a guestimate or based on based on "real world" experience? Your reply may help me determine if some unlabled steppers I have will work reliably in my first router.

[Jonathan]

I would like it to cut Ali is there a reason you think it's just a woodworking machine? What have I done wrong lol?

Er, not sure really... maybe the MDF bed. That wont stop it working, but my router bed is currently MDF and it is rather limiting.

If you wanted to test the R2020 screw and nut I don't have a problem sending some over as long as you send them back when your done :-)

Thanks for the offer, but it wouldn't really be practical/worth it .. I'll just wait and see how it goes on your machine.

Was the 3x figure a guestimate or based on based on "real world" experience? Your reply may help me determine if some unlabled steppers I have will work reliably in my first router.

I used 3x because that's what's in irving's motor calculation spreadsheet. In reality I got a lot better than that - if you include the inertia of the pulleys in the calculation it's quite a lot more accurate.

[D-man]

The mdf bed is only 5mm lol it's only there to rest all my junk on lol I'm hoping to get some small extrusion to give it a nice solid bed. However this is in the future wood and plastic is its need for now.

[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/

[boldford]

I used 3x because that's what's in irving's motor calculation spreadsheet. In reality I got a lot better than that - if you include the inertia of the pulleys in the calculation it's quite a lot more accurate.

Many thanks for the pointer. That's really useful information which may save me some grief.

[jcb121]

I'm just wondering, that timing pulley you used? was it around 26 teeth 5mm pitch?

[Jonathan]

I'm just wondering, that timing pulley you used? was it around 26 teeth 5mm pitch?

For the one in post #61 I used a 30T HTD 5m pulley. Clearly it depends on the ratio you require, but if you can keep the pulleys small that helps a lot with reducing the moment of inertia of the rotating assembly.