I am currently building my second table due to some problems with the first. The first was a small 2x3 table that used sliding glass door bearings on 1/4" round bar for linear guides. I used ACME threaded rod to provide the power. The problem was that getting a straight threaded rod that didn't whip and induce noise into the machine was impossible. So this lead me to timing belts as they should not have the same problems. Of course the switch meant that I had to rework most of my gantry. The original design used dual steppers on the X and a single on the Y. Turns out that my cutter needs to lift off to start the arc so I needed to power my Z axis also.
All of these problems have led to me just biting the bullet and building a 4x5 cutting surface table. To open up my controler to be able to handle the Z axis I am going to use one stepper to drive the X axis. This means I need to do a driveshaft across the table to turn the two pulleys that will power the X. The plan is to have the gantry walk back and forth on a stationary belt. I am doing this so that upgrading to a longer table later is not a problem and also to make it easier to break the table down and move it.
I have the option of making this driveshaft out of either 1/4" or 5/16" solid rod. The problem is that 1/4" is really common and 5/16" is harder for me to get locally. To be honest I am not sure that either one will not twist along its length under the torque required to move the gantry. My entire gantry is going to be around 15-20lbs. Plus the force required to drag the plasma supply hose around.
Which size should I go with? Do I need to go bigger? Where do the pulleys come from for larger rod? I can get 1/4", 3/8", and 1/2" or larger easily locally. The 16th inch sizes are special order.