On 24/05/2021 21:23, newshound wrote:
On 24/05/2021 20:49, Fredxx wrote:
On 24/05/2021 20:13, Murmansk wrote:
I have a circular saw jig which I made myself and it uses bits of
aluminium which are L shaped in cross section for the saw to run in.

I'd like to make a better one with longer "rails" and rather than
using the L shaped strips, which tend to sag, I'd like to use tubing
and I know you can get some things that run along tubing and probably
have ball bearing in, but I can't remember what they're called.

Can anyone tell me what these are called please so I can look them up
online

IÂ* would call them linear bearings. They can be fully circular or
part, so to fit round shafts or guide rails respectively.

so:
linear bearing pillow
linear guide rail

An idea:
Â*Â*https://www.youtube.com/watch?v=UB80HojMDyg

Yes, linear bearings. Available with or without shafts from people like
Euro Bearings.

They need to run on pretty accurate rod or tubing, which will add to the
cost. I'd have thought you could get away with plain bearings, probably
using one of the engineering plastics. Oilite bronze (on steel) would
also work, but oiled or greased brass/bronze on steel would tend to
attract sawdust.

Ground steel rods are pretty common. Its then how you mount the rod,
whether to support it from underneath as per the video or at each end.

Most 3D printers use ones supported at each end, allowing for a complete
circular linear bearing.

I have seen the ones on guide rails used on very large machines such as
CNC routers.

The bearing will have seals which should keep dust and sawdust out of them.