[panozeng]

I lucked out last week while at my local scrapyard and picked up some sort of machine that included 6 1" Thomson double width open pillow block bearings, 2 42" rails, and 2 16" rails along with a good bit of 1/2" aluminum plate for $1.50 a pound. The bearings are in very nice, clean shape - what a steal!

Anyway, I needed one pair of bearings for a tube positioning carriage on my mandrel tube bender, and that leaves me 4 bearings for the plasma gantry I have been planning on building. I'll just have to get more rail. I was wondering how much torsional force a 1" open pillow block style Thomson bearing was designed to handle. In other words, if I have one of these on each end of a 60" long carriage would I need to have a drive on each end to keep it from twisting? Or would the bearings be more than capable of holding the carriage square with the rails with the drive being on only one end? I know it depends on how fast I'm accelerating, the weight of the parts that are moving, etc. But, I will only be using this for plasma, so no cutter forces at least. Any thoughts?

Thank you,
Jason

[smarbaga]

hello
i think if these bearings are at least 8 inches apart and you are using this for a plasma cutter, i don't think they will twist with the supported rails.
this is just my thought.
i would make provisions for a drive on the other end just incase one has to be added later, or you deside to put some other kind of cutting tool on it.
this is just my guess.

[Jason Ross]

Use a 1:3 ratio for a 60" wide table use 20" on center or as close as possible. Otherwise you will get crabwalking and binding. They do not have the torsional capcity of a profile or square rail.