Here's a device that might have some merit. I don't know the price, but saw one a long time ago

http://www.amacoil.com/html/rs_01.htm

Its a ball screw without threads.

Out of interest how does it work?

If I remember correctly, there were 3 cam followers placed around the shaft. These cam followers were set on the pitch angle and were under tension on the shaft.

Turning the shaft caused the bearing block to move based upon the pitch of the cam followers.

Check the website for more details.

A couple of manufacturers have used them for positioning on their brake back-gauges, they work pretty slick, they typically use linear scales for positioning though, rather than on the end of the motor, which is mounted direct drive to the end of the shaft.
The reason is they are OK for consistent light loads, but if they encounter an obstruction, slip can occur, the motor's turning without any motion on the bearing block.
I think if they are used on consistent predictable loads they work great.
Al

So this linear guides are backslash free but what about errors ? Only if slip occur?

Do somebody knows how much this linear guide costs compared to a ballscrew rolled or ground?

But I can see a few potential weaknesses. Slip is the primary one, which will potentially limit its load capacity.

Here's how it works...
http://www.amacoil.com/html/page3a.htm

Basically, it just leans a bearing at an angle, and the pressure angle causes it to track along the length of the linear slide. Positively brilliant. In fact, one of their designs even has an adjustable "thread pitch" that's remotely controllable...can you imagine the possibilities for CNC?

I have some bearings, and some linear slides from an old inkjet printer -- maybe I'll play around with them, a bit, and see if I can get something working!

Anyone else done this, already?

-- Chuck Knigt

I have a bit of a concern!

Those angled rollers are touching the shaft on a very narrow [contact area] if I'm
correct, therefore premature wear must be considered??

Konrad

Yep, and the angled roller merely provides a larger contact area, than a traditionally shaped roller. Your concern is correct.

A thought occurs to me, though. Since the angle of the roller is adjustable, wouldn't it be possible to "tweak" the system to increase the contact patch, as wear occurs?

-- Chuck Knight