1.7*0.74*0.4m Mill / Router building...

[Jonathan]

Very nice machine you have there Jonathan

Thanks, but it's not that great really...quite a few things I'll be changing as the gantry is not strong enough for what I want to do next.

did you get anywhere with the 'twisted bearing' screw drive setup ?

Yes, I mounted it and it worked well with low backlash:
http://www.mycncuk.com/forums/router...html#post16838

It's clearly not as good as a real ball-screw, but as something to get started it's excellent due to the low backlash and very low friction.

I cut the first piece with the new bed last night - just a pocket in the back of an aluminium motor mount and the finish was much better than with the [edit] MDF bed and I didn't need to do a finishing pass to get that.

[TrickyCNC]

Yes, I mounted it and it worked well with low backlash:
http://www.mycncuk.com/forums/router...html#post16838

It's clearly not as good as a real ball-screw, but as something to get started it's excellent due to the low backlash and very low friction.

I saw you have mounted it, what I could not tell from reading the rest of the thread, is if you kept it / still use it ? and if so, how it was holding up ?

Rich

[Jonathan]

I used it for quite a long time, until changing to an RM1610 ballscrew. It was working well, although had caused some wear to the M16 rod (although not enough to be a problem) due to bearing inner ring being significantly harder than the screw, however I think if you used springs to push the angled bearing against the screw and/or used a trapezoidal lead-screw instead then it would last a long time.

[JAZZCNC]

I cut the first piece with the new bed last night - just a pocket in the back of an aluminium motor mount and the finish was much better than with the aluminium bed and I didn't need to do a finishing pass to get that.

Surely that should read MDF bed.?

[Jonathan]

Surely that should read MDF bed.?

Yes, thanks for pointing that out - fixed.

What size fly cutter do you use for surfacing yours?

I'm cutting the aluminium angle now to fit round the sides for the coolant barrier, then once I've got the bed aligned I'll get the router to cut a suitable hole in the bed at one end for the coolant to flow through and make a filter etc...

I seem to be able to cut 3mm per pass with the 6mm single flute cutter now :)

[irving2008]

What have you done there? Can you give some more detail


edit: *** must type quicker ***

[Jonathan]

What have you done there? Can you give some more detail

Er, not much more to say really? Standard thin section bearing with bore bigger than the thread (20mm here, but more would be better to get less axial load on the bearing) placed on the thread at an angle. I'll use a strong spring to pull the bearing against the thread so that it rides over any imperfections. That's what the tabs are for on the mount, to mount the spring.



I'm toying with the idea of pressing a brass insert into the bearing lathed to better fit the 60° thread profile. It's tricky to work out the exact dimensions though...

[routercnc]

Hi Jonathan,

Interesting idea, but it's got me a bit puzzled. If the thread rotates, and the bearing rotates with it, how does it progress along the thread? For a nut in a thread to progress, one part has to rotate whilst the other stays still. Yet in the video the bearing inner and the thread are both rotating. Is it perhaps vibrating it's way along? If so I'm not sure this will give reliable position control.

The only way I can see this working is if you removed the inner race (somehow) to create a pseudo ballnut. Or maybe I'm missing something here so please enlighten me!

[Jonathan]

]
Interesting idea, but it's got me a bit puzzled. If the thread rotates, and the bearing rotates with it, how does it progress along the thread?

Er...it just does!
The bearing is rolling on the thread properly, not vibrating. It's difficult to explain and visualise. Try just getting a random bearing and screw and fiddle with it, you'll soon see how it works!
If you imagine the inner ring of the bearing was stationary then clearly it would still work...just like a normal nut. The inner ring rotating makes no difference to this, except of course giving rolling friction.

Sorry I can't really explain it any better!

One slight issue I can see with this is the bearing applies torque to the screw, trying to bend it. This could be solved with having two bearings angled opposite to each other but I think M16 is strong enough for this not to be an issue.

I'm in the workshop at the moment..lots of tapping, joy!

[Wobblybootie]

Ummm like this???