linear rails

[MikeW1966]

Hi,

I am building a cnc router with 2" x 5" steel tubes I am trying to decide wich linear rails to use. I am looking at these 20mm round rails and bearings from GMT Glacern Machine Tools - Linear Rails and Bearings 103" long or the cold rolled steel and carrages from cnc router parts.
Does anybody know if the 20mm rails would be strong enough for an eight foot machine and wich rails would be better and what would be easier to install.
Thanks for the help.
Mike

[DonFrambach]

I built a small router using both glacern 20 mm rails and CNCRouterParts linear carriages. Both were easy to install and worked very well. I chose to use the Glacern rails for my horizontal axis because I was concerned that the horizontal axis situated below my cutter could get fouled with dust. I chose to use the CNCRouterParts carriages for the gantry and Z axes because I did not want to mount the round rails in a manner where the cutting motion would tend to pull the carriages out of the rails.

Regarding strength. Both were plenty strong for my purposes. I would imagine that you could build an 8 ft machine that could overstress both systems. But for the kinds of work that most people are doing either one should work fine.

[louieatienza]

As far as more accurate, the Glacern might have the advantage since the bearings run on fround hardened rod. The CNCRP run on CRS rails, so your accuracy will rely on the accuracy of the CRS. A lot of people use it for 8" axis (and one here a 12' axis) just fine. The only big advantage I can think of for the Glacern is that you can spread the bearing blocks further than having a single CNCRP block, and the gantry could withstand a higher moment, but with 103" rails, if you want 8' cutting area you're kind of limited to a 7" max spread, which is less than the length of a long CNCRP block.... You also don't have to drill a lot of holes to mount the Glacerns, where you'd have to drill a lot of holes on the CRS stock to mount to your frame.