Hi, i am currently designing my first cnc machine, and im going to build it completly out of aluminum, i just wanted to know if an 8" width is alright for t gantry sides with a total travel of 36". Furthermore, I plan to machine aluminum quite often, if the sides are made from 1" thick aluminum would this be rigid enough. Any suggestions would be greatly appreciated.
A 1"x8" side plate at 24" high cantalevered at the bottom only would deflect 1/16" under a 100lb side load. Two plates (which you'll have) 1/32" That's as far as beamboy can get me. I'd have to use the fancy FEA software at work to figure out the deflection when you add in a cross piece oriented vertically across the back of the gantry. That'll stiffen it up considerably. You could always bolt on ribs to the outside of the side plates if the open span between the bottom and the back piece seems to flex too much. I don't have a good feel for the cutting forces for aluminum, but someone else might.
As far as the 8" width for the linear bearings, skate bearings, whatever, it might be on the narrow side, making the gantry more prone to racking. I haven't gotten my machine, which has about a 7 1/2" span with skate bearings far enough along to get a feel for the racking issue.