Originally Posted by
ahren
Jim,
Got your email -- it looks like you answered your own question with regards to the extrusion style to use. A benefit of using anything in the 15 series (3030 included)is that you can use my rack clamps to make things bolt together really squarely.
I do agree with Steven that the R&P for the z-axis is a lot more trouble (and expense) than it's worth. You'll get better control and similar speeds with a 5 start ACME solution, and the thread angle on ACME makes it such that back-driving usually takes quite a bit of force, so you don't need a brake or worm gear to hold the axis up when power is off.
I would also suggest (for cost and simplicity) that you use my carriages and the rack turned sideways for your gantry -- that way you don't need the funky bracket coming off the back (which worries me -- this needs to be stiff, as the entire motive force for your z-axis is being transmitted through this), and you can use regular cold rolled steel for the gantry rail without having to grind 45's on it.
Best regards,
Ahren