I recently purchased a Shapeoko XXL that arrives in a few days to prepare I want to build my table for it. Like it says in my title I was thinking about using steel tubing to make my torsion box tabletop since I do not have a planar and a joiner to make sure than 2x4s I would use are flat.
Would steel tubing work in this case or is that not straight enough either?
I am not sure what the fuss is about. My XL sits on a table top and works just fine. The accuracy always surprises me, I find that everything it does is within a few thousands of what it should be.
I am not sure the stepper motors are powerful enough to cause the machine to flex to the point that additional support would be needed.
At times there seems to be the desire to do things because they can be done. I am more inclined to fix problems after they exist and not before.
The steel would work but the expense would be much more than using mdf. Plus during welding the steel may distort and would require a lot of grinding and you would still need a plywood base on top of the torsion box. If you have a table saw then making the pieces would be easy and precise. Make a shooting board for a circular saw and break down the MDF into smaller pieces before trying to cut on the table saw. I have a Powermatic 66 with 52" fence and I avoid cutting plywood in full sheets. The wood whisper on youtube.com has a good video about making a torsion box. My current table is 4x4 legs with 2"x10" apron with a doubled up plywood top that is 4x4’ (XXL) and has castors so I can move it. This is adequate but it came with the Shapeoko when I bought it used. I will be making a torsion box after Christmas. Right now Santa is busy putting the last minute touches on all my gifts.
Steel tubing might be overkill, but it will have a wooden surface that you will have to surface flat, so if the frame is not perfect it wont hurt you, but same goes for a wooden one. It’s the top that will be surfaced flat.
The XXL does flex in the center, but I added 2" thick foam insulation under mine, and that solved it. I just let the frame kind of sink into it, and the feet dont even touch the table anymore.
MDF or plywood is the way to go. The strength of the frame is enough that the minor deviations of the table will likely not transmit through the machine. If accuracy is needed at that level, you will be machining a level surface anyway…