Differencial Roller screw (like a ballscrew but free!- almost)

Hi all,

I spoke to Mike he's happy for anyone to use this invention of his see the video [www.dropbox.com]

its very, very accurate and with no backlash its as good as ball screw - plus we can print it so its almost free!, I'm using it as part of a small cnc lathe build (part printed of course)

I'll have all the design details at the next meet up.

Cheers

Nick

Edited 1 time(s). Last edit at 09/06/2012 05:23PM by ncibbit.

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Using ABS Prusa Mendel from Indieflow (eMaker website) with Pronterface and slic3r (0.9.2) . Printing with 3mm PLA through home constructed J Head hotend and Wade Herring bone Geared Extruder. Sanguinolulu board running Marlin

Looks pretty impressive. Interested in how the threads are calculated. I would be interested in experimenting with this. However I would be making a metric version.

Hi, this is a really interesting idea, but unfortunately I get a 404 error when I follow your link. Has it been deleted?

Hi all try this link
[db.tt]

Cheers Nick

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Using ABS Prusa Mendel from Indieflow (eMaker website) with Pronterface and slic3r (0.9.2) . Printing with 3mm PLA through home constructed J Head hotend and Wade Herring bone Geared Extruder. Sanguinolulu board running Marlin

Ah, right, it's based on Mike Everman's video on youtube here: [www.youtube.com]
Thanks for the link. You didn't tap the inside of the bearings, or use a steel insert like Mike? It's just held on the thread using friction, and moves up and down just through pressure on the threaded rod? What's stops it slipping on the rod? Did you offset the top and bottom bearings so the threaded rod runs in the centre of the block?

Sorry for all the questions, it is an interesting idea. I think it would be better to have the inside of the bearing threaded, like Mike did, but it would have to be a special thread I guess.

Sorry for the delay in replying.

Yes it is just like Mike's, it is Mike's - except its printed- I've spaced the bearings out and can adjust the distance between them with the studding that holds together( I've know Mike for many years now so asked him if it was Ok to do a printed one- the folder link is called the Everman roller bearing) .
There is no thread on the internals of the bearings but there are brass inserts which are circular ridged to the same pitch and profile as the threaded rod, in my case 0.8mm pitch (M5) so that the bearing rolls around the threaded rod. The inserts only contact a part of the threaded rod so its able to do this.
The two end bearings run in the centre of the block the middle one is offset, or rather is capable of being off set - see the pics - by a bolt.

Hope that helps clarify things a bit :-)

Cheers

Nick

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Using ABS Prusa Mendel from Indieflow (eMaker website) with Pronterface and slic3r (0.9.2) . Printing with 3mm PLA through home constructed J Head hotend and Wade Herring bone Geared Extruder. Sanguinolulu board running Marlin

Thanks for the clarification, just trying to get it right... so a couple more questions!
The rod that it runs on is 0.8mm pitch M5?
The brass insert - pressed-in interference fit?
The brass insert - what thread is it actually tapped with? 0.8mm pitch with a 6mm diameter? Or actually just M5 like the rod, and the clearance around the rod creates enough movement to circulate around?
Thanks. I'd really like to have a go at making this, to see how well it functions.

Hi,

again sorry for the delay (i'm not getting email alerts for some reason), anyway here goes....

yep its an M5 rod with 0.8mm pitch, the brass inserts are pressed into (and loctited) into place in the bearings

I can see where the confusion is I think, the brass inserts are not tapped at all, they have concentric grooves cut into the inside face at the same pitch distance as the M5 rod.

I do this by holding the brass insert in the lathe chuck I then use an old straight section M5 tap held in the tool holder to cut the grooves.
I set the lathe running and put the tap into the middle of the inserts hole, its not touching the holes sides at the moment, then just wind the topside over so that the teeth of the tap cut the concentric grooves (it only take a moment at 0.8 pitch) re-centre the tap and wind the bed back to bring the tap out of the insert hole, hey presto concentric groves at exactly the same pitch as the M5 studding.

The diameter of the brass inserts is not relevant, all it needs is enough clearence so that the M5 rod can rotate within it without the back of the rod contacting the other side of the brass insert, what ever you do if you put a, M5 rod in you will get a 0.8mm pitch out, pretty neat i thought - Mike's a clever guy!.

hope this helps

cheers

Nick

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Using ABS Prusa Mendel from Indieflow (eMaker website) with Pronterface and slic3r (0.9.2) . Printing with 3mm PLA through home constructed J Head hotend and Wade Herring bone Geared Extruder. Sanguinolulu board running Marlin