# A cheap alternative to ball screws



## samthedog (May 30, 2014)

Hey guys, I just stumbled onto this:

http://www.thingiverse.com/thing:112718

A vid in action

https://www.youtube.com/watch?v=Rkhm-hp9788

From this demonstration, I think this is a real alternative for ballscrews. Apparently the technology is about 30 years old but I have never seen anything like it before. 

Anyone tried this?

Paul.


----------



## tcarrington (May 30, 2014)

we used these back in the early 80's for an X-Y type application. 
worked well for use by humans who would compensate for small slippage. 
if the axes have little or at least a constant load, then probably OK. 
But they do slip, affected by foreign material on the shaft, and are sensitive to small mechanical variations in the components. 
They are incredibly interesting though, aren't they?


----------



## RandyM (May 30, 2014)

Wouldn't a cog or gear belt work just as good? Particularly with DROs.


----------



## dave2176 (May 30, 2014)

I can see this being useful in a low torque condition like a 3d printer but question its ability in a mill.

I got a set of 3 c7 grade ballscrews with double ballnuts for zero backlash at $189 delivered for my rf45 clone. I don't think I could do better with other technologies.

Dave


----------



## samthedog (May 30, 2014)

I know there are other options such as toothed belts and so on but found this a nice home made option. If the rod material is rougher in texture I wonder if the torque needed to make it slip would increase.

No doubt that ballscrews are dropping in price, I just figured that this is a nice home brewed alternative.

Paul.


----------



## John Hasler (May 30, 2014)

samthedog said:


> I know there are other options such as toothed belts and so on but found this a nice home made option. If the rod material is rougher in texture I wonder if the torque needed to make it slip would increase.
> 
> No doubt that ballscrews are dropping in price, I just figured that this is a nice home brewed alternative.
> 
> Paul.



It would also help to give the rollers a concave shape that would "envelop" the rod thereby increasing the contact area.  Tricky to machine, though.


----------



## countryguy (Jun 2, 2014)

hi,  Could you offer a name you used for those?    I do need to replace my Z axis or at least dig into it a bit.  
Since it is so short, it may just be easier to replace it w/ these prices!   Thanks,  CG 



dave2176 said:


> I got a set of 3 c7 grade ballscrews with double ballnuts for zero backlash at $189 delivered for my rf45 clone. I don't think I could do better with other technologies.
> 
> Dave


----------



## dave2176 (Jun 2, 2014)

countryguy said:


> hi,  Could you offer a name you used for those?    I do need to replace my Z axis or at least dig into it a bit.
> Since it is so short, it may just be easier to replace it w/ these prices!   Thanks,  CG



Stores.ebay.com/linearmotionbearings contact him if you want something not listed like the double ballnut or different length etc.

Dave


----------



## ddmunroe (Jun 2, 2014)

I found this interesting the trick would be knowing how much to vary the bearings inclination in order to achieve your desired rate of travel for the spindle.
Agree it has limitations but quite good.
Thank's for posting
dd


----------



## samthedog (Jun 3, 2014)

From what I could tell, there are different types where the bearings are steeply angled, allowing fast traverse of the rod, to very shallow giving a very controlled movement. I am not sure what the difference would be in holding power between them. Contact area between the rod and the bearings is quite small so the holding power may also increase with a larger rod diameter and bearing size.

Paul.


----------

