Questions on modifying a Shopbot

[WayneC]

I'm getting ready to upgrade my Shopbot PR model CNC. I'll be replacing the gantry and Z axis, and upgrading the X rails, as well as the controller.

I have a couple of questions about my design for a new gantry. My design is most like the Tech Isel LC machines, with a single beam held by steel posts on either end. I'll put HiWin guides on the top and bottom edges of the beam, and the Z axis car will ride on these. I understand that the farther apart these guides are, the less likely the Z car is to flex or twist around the beam's axis. I also understand that I must balance that with the drawback of inertia problems that a wider and heavier beam would create.

SO, how far apart should the guides be to reduce flex to tolerable levels? What width of beam would you guys recommend for CNC router? Its gonna be used for woodworking, with a Porter Cable for now, but later a 3hp spindle.

Thanks for the help!

Wayne from White Salmon
ShopBot PR 120/60 with Porter Cable router- a great place to start