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EvanRobert
06-29-2003, 01:26 PM
I have not seen anyone use 80/20's linear motion bearing for a CNC Router solution.

I saw in another thread the UHMW-PE has is spongy and has a high coeffieicent of expansion. Others said this was OK for routing wood and aluminum.

This seems like such an obvious solution to the CNC router platform there must be some drawbacks or everyone would us these supplies.

Is it cost?

Thanks,

Evan R.

P.S.
The web page for 80/20 is:
www.8020.net (http://www.8020.net)

ToyMaker
06-30-2003, 12:56 AM
Evan:
I saw a discussion of the 80/20 slide bearing where the author voiced a concern about the remark on their site "can be shimmed for precise fit".
How loose is the stock fit, and how tight do you have to shim it for a given degree of precision?

robotic regards,

Tom

georgebarr
06-30-2003, 10:46 AM
I had considered using UHMW type linear bearings that 8020.net and tslots.com sells. I was informed from sources that it uses pads rather than bearings that roll along the rail. The pads slide or glide across the aluminum extrusion. The same companies that sell the UHMW bearings also sell shims to close-up the distance gap to make the pads fit tighter. However, the problem with tight fitting pads is slower slide speeds which means your motors will have to work harder so don't expect tight fitting pads to be fast in moving along your axis. Some complained that it takes many tries to get the right tight-fit. One good application for UHMW bearings is that it is able to withstand harsh environment where liquids might spill on your bearings. The bearing pads can wear out but the price to replace just the pads is inexpensive. One major problem that I found is since the UHMW bearings does not use a rigid and sturdy rail like the thk bearings use, it is possible for the aluminum extrusion that the UHMW bearings glides on to bend since extrusion is not as rigid as thk rails. You would have to solve for the problem when weight is applied to the UHMW bearings and extrusion and the problem of the extrusion bending even in light loads. You can make your extrusion rigid by mounting the metal angles along the beam so it wont bend under weight. Sources say for precision, use thk bearings or anything similar. I had considered the UHMW bearings since it simplifies building a cnc but after hearing about its many problems I decided to go with using thk bearings. I decided to take more time and planning to build one good cnc machine rather than building 2 or 3 mediocre cnc machines.

Thanks,

Bill
06-30-2003, 11:22 PM
check out this site www.campbelldesigns.com it might help out

cncadmin
06-30-2003, 11:31 PM
Try these guy's here http://www.tslots.com/

balsaman
07-01-2003, 04:56 PM
I have seen those slides from 80-20 in real life. There is too much surface area IMHO to make a good slide. All that bearing surface area will cause too much friction it all the play is shimmed out. They would be good for an application that needs to be loosened, moved, then retightened.

Eric