Spacing for Thomson round rails

[bgolash]

Hi All

I`m wondering if any one has specs on the spacing of round rails. When I did my diy cnc machine I spaced the blocks 18 inches. I can twist the X axis .008 to .010 by pushing against the Y axis. Even with the looseness in the linear motion system it works OK for wood but I`d like to machine aluminum and steel. I`d like to increase the spacing but will lose travel in the X axis. Somewhere I heard that if your machine was 36 wide that it was necessary to space the blocks 36 inches apart.

Barry

[ger21]

Would it be easier to convert to a dual screw drive?

[jhowelb]

I think what you are talking about is "racking" where one end of the bridge advances farther than the other. This usually causes binding or at the very least parts that are out of square.

If that is the case you might find some assistance here. (I did!)
Make your Gantry rock solid!

[fatal-exception]

I have the same type of setup as you, hanging the gantry from the rails. I'm in the process now of turning them upside down, so that the gantry rides on top of them. The Thompson rails that I have are not meant to be used in the hanging position.

Anyways, my machine is smaller, with the gantry width at 30", and my blocks are spaced at 8". I've never had a problem machining aluminum, just some weird oscilations at about 250ipm rapids, which is what I'm trying to fix. Faster is fine, slower is fine.