Re: [CAD_CAM_EDM_DRO] UHMW slides

george_barr wrote:

>I have a question. I am building a CNC (hobby) and need it as
>accurate as
>possible.
>

What does this mean? "Accurate as possible" has no limits. The
semiconductor wafer
fab guys use million dollar air bearings slides with laser
interferometers for position
sensing. Some of the wood router folks are satisfied with 1/16" accuracy.

> I am using aluminum extrusion from www.8020.net. They
>have these
>linear bearings which uses UHMW instead of ball bearings for slides.
>These
>slides uses slippery plastic like pads, instead of ball bearings, to
>glide
>along the aluminum extrusion. Does anyone have any experience using
>these
>types of slides? They said a shim can be purchased to provide a more
>exact
>fit with the slide and the extrusion beam.
>
>I don't want to waste my money if these slides are not worth it. I
>plan to
>do PCB (circuit board) work with my cnc so it needs very good
>accuracy.
>
>

I doubt this will work well, or for very long. Aluminum is a HORRIBLE
bearing surface,
although hard anodizing or nitriding makes it better. If you will be
milling out circuit
board traces and drilling holes, you will be generating lots of abrasive
dust that will eat
the slides and plastic sliders. I'm not sure what is the best or most
durable scheme for this
use. I would think rolling elements would be much better at tolerating
this dust. Sealed
ball bearings used as wheels that roll on some sort of way sounds like a
good design, as
the way and rollers can be easily cleaned when necessary. A toothed
belt used like a
drive chain would be a good choice for linear motion conversion, as it
won't need any
lubrication, and lubes make dust stick.

Jon