Re: First Build-What comes first... Ball Screw? Spindle? Linear Motion System?
Given that you are not trying to build a spacecraft where every ounce counts, this really does not need to be over engineered.
You can cut aluminum (or steel) with a Dremel tool, but not very fast. I guess I would start with how much electric power do you have available to run the spindle motor. This will dictate the maximum spindle power/size. Once you have chosen a spindle, look at the published shipping weight of it, that's close enough.
Take a look at the rail load spec's for various rail/car combinations. Just keep these spec's in the back of you mind for the moment.
Then add up the mass of all of the bits & pieces that make up the gantry assembly, including the Z axis hardware and spindle. This gives you the moving mass. Then decide on the acceleration rate that you want to achieve. F=MA Force = Mass x Acceleration. This will dictate the ball screw/axis motor combination required. Don't forget to look at the torque curves of the axis motors. Stepper torque drops off rapidly as the RPM increases.
All of this will give you a starting point for doing the calculations.
Or based on your spec's, you could throw out everything I said above and go with some 2005 or 2010 ball screws, 20mm rails, and around 1200 oz/in axis motors and build the machine.
Jim Dawson
Sandy, Oregon, USA