[posix]

It is surprising to find out that no one on the forum has ever mentioned a roller screw.

They seem to be a lot more robust than ball screws and look like something that could possibly be even made at home (a home equipped with a workshop and a lathe, that is )

Anyone ever pondered on the idea?

[Evodyne]

Posix,

That's different. First time I've heard of/seen one. Any more info?

Lance

[posix]

It's pretty, though, ain't it?

Well, it works on the principle of planetary rollers - think along the lines of a rear diff on a car - the screw turns, little planetary rollers (smaller diameter screws with the same thread depth and pitch) roll in opposite direction (just like balls in a ball screw) around the circumference of the screw. The little planetary rollers also roll INSIDE a nut wich, also and predictably, has the same thread depth and pitch. So looking from the side at the whole concoction you in effect end up with a normal bearing with the shaft (screw) in the centre, balls or rollers (planetary roller screws) around the shaft and race (nut) on the outside.

I'll see if I can dig up a few drawings to make things easier to picture.

[posix]

Ok, here's another couple of cut-away drawings. Also note that little (planetary) rollers have little pinions at both ends and the nut has a corresponding large toothed ring on each end. My guess is that's to discourage the rollers from "sliding" across the screw and nut surfaces but to turn properly. I've caught mention of gearing somewhere as well.

Could any of you solidworks gurus out there make up a solid model of this which could help us visualise the whole system. Also mechanical engineers among you could come up with a spreadsheed which could be used to calculate the exact screw, roller and nut diameters and thread depths and pitch of each component since this mechanism isn't using any standard threads.

[nachini]

I already had seen it in a (Hungarian?) Web.

http://www.hobbycnc.hu/CNC/Otletek/Otletek.htm

The Web is partially translated to English, but there is no explanation in English about the screw.

Somebody can translate it?

Hey, this is my first post!!!

[Evodyne]

I already had seen it in a (Hungarian?) Web.

http://www.hobbycnc.hu/CNC/Otletek/Otletek.htm

The Web is partially translated to English, but there is no explanation in English about the screw.

Somebody can translate it?

Hey, this is my first post!!!

nachini,

Can't help with the translating, but welcome aboard. Watch out-this site can be addictive! Enjoy...

Lance

[motomitch1]

http://www.exlar.com/products/linear...rew_oview.html

[Dave's_Not_Here]

Here is a web site with some good explanations...
http://www.exlar.com/products/linear...ew_basics.html

[Evodyne]

It's definately neat. But it probably fits the typical model: if it looks complicated, it's expensive. If it looks expensive, it is expensive. If it looks expensive AND complicated...well like they say, if you have to ask the price you probably can't afford it. Bummer.

Lance

[swoolhead]

This is a good link http://www.exlar.com/products/linear...RolScrew12.pdf it's good some good pictures in it.

Looks like the standard nut has 0.01-0.03mm of backlash on it, but there is also a preloaded version. I am intrigued to know how it compares to something like this http://www.kerkmotion.com/ which claims zero maintenance with zero backlash, but there are no real values quoted, but does look a lot cheaper.

Stephen

[Geof]

An interesting point to note in the RolScrew12.pdf that Stephen gives the link for is that the machine tool applications that are mentioned are either high force or high speed but not high precision positioning. It could be that these screws can outperform ball screws in force and life but do not match them for accuracy and precision.

It would be interesting to try and build something of this nature using different sizes of threaded rod with the same pitch.

[ViperTX]

Well...just a quick glance and it appears to be less efficient then a ballscrew because of the increased number of parts that rub on the screw...okay, maybe they are suppose to rotate against the screw....it also has more moving parts that appear to require some precision in how they are mounted....those little planetary screws....they appear to float some....

[posix]

I don't know but all material I've managed to come across lists roller screws as having superior accuracy and repeatability to ball screws and due to the large number of contact points also exhibits better stiffness and load resistance.

But all this is way beside the point. What I wanted this thread to concentrate on is making a DIY version of it as ball screws are nigh on impossible to make at home and these suckers look a lot less complicated.

And here are some examples of what people have allready done, albeit much simpler and cruder versions of what the real deal looks like:

[posix]

Well, hello everyone.

Today I had a productive day. For roughly $15 and in 15 minutes of cutting time I had my own roller screw. And I can tell you this thing beats any delrin nut any day. Ok it has some backlash, it does have some axial play as well but considering it's been made out of M10 "allread" and with only an idea in my head and no drawings of any kind, planning or anything else for that matter (even the cuts are as rough as they get - no polishing or finishing of any kind) this thing rolls really nice.

Now on thursday I'm going to put some plugs in my ears and go to the same guy with the drawings of a real roller screw and he told me that from what he made today and from what I explained to him about the real roller screws he could do something.

I'll try and upload a few pics of what I had made today. This is fantastic! Cheap homemade better-than-ballscrews roller screws are coming!!!! :wee:

[DieGuy]

I could envision putting a gear train on the rollers and driving that instead of the main screw as well, just look at that last picture and think gear driven.

[posix]

Some images of what I've got:

P.S. sorry about the resolution; I have a feeling my digital ixus is going to pack up soon due to the lack of use... :frown:

[swoolhead]

All the home made designs seem to be missing the planetry gear that slaves all the screws together. I wonder what difference this makes?

Nice work BTW!

Stephen.

[posix]

I haven't forgotten the planetary gear or the outer threaded shell but this was a test just to see how easy it turns and if the concept is ok.

The next phase is to take one of the cutaway drawings of a real roller screw together with all the elements and make the real mccoy, custom threaded rod, little threaded and toothed rollers, outer threaded shell, the works. Can't wait 'till thursday... :banana:

[Evodyne]

All the home made designs seem to be missing the planetry gear that slaves all the screws together. I wonder what difference this makes?

Nice work BTW!

Stephen.

If you look closely the gears DON'T tie the screws together-directly. They mesh with a ring gear. Here is my take. The little gears can't be of a larger diameter than the threaded piece they are attached to: the main screw would never fit though. But they could be the same or smaller diameter. If they were smaller, the ring gear would need to be resized to mesh properly. But changing the relative diameters affects he "gear ratio" between them. Thus, for a single turn of the body, you could get more or less rotation of the inner screws. If they spin faster, then the main lead screw will travel further for a given amount of nut rotation. So the ones without lose nothing-they are just operating at a "fixed" design point.

Posix, I posted earlier and said I thought this looked complicated/expensive. What you have done has changed my mind. I'm really impressed by the way you dove right in and tried it. Way to go!

Lance

[Evodyne]

I haven't forgotten the planetary gear or the outer threaded shell but this was a test just to see how easy it turns and if the concept is ok.

The next phase is to take one of the cutaway drawings of a real roller screw together with all the elements and make the real mccoy, custom threaded rod, little threaded and toothed rollers, outer threaded shell, the works. Can't wait 'till thursday... :banana:

Thursday, huh? You ambitious little devil, you. Question: how have you resolved the threads, pitches, etc? Inquiring minds want to know....

Lance