With the torsion beams completed, I laid them out across two sawhorses and used shims under the legs to get the torsion beams level in both directions. I placed a sheet of MDF on top of these beams and proceeded to build up the base for the machine.
As you can see below, the pattern of webs is not uniform. I was originally planning to have it filled with the square pattern seen at the ends. However, I changed my mind and decided to go with a sparser pattern. It should provide plenty of rigidity for this prototype.
The glue-up was done in two stages, first to attach the sides and all the webs to the base, then to attach the top. Many clamps and weights were used to hold everything together while the glue dried. With the top in place and everything glued up, the assembly is very stiff and doesn’t flex at all when lifting up on a corner.
Here is the Z axis carriage after unclamping from the glue-up and giving it a light sanding. I am using aluminum bar stock to mount the profile rails. I chose this method in case I wanted to mill a perfectly flat surface on these or to mill shoulders (the preferred mounting method for HIWIN rails). At this point the bar stock is just positioned for a test fit. They will be epoxied in place after drilling and tapping the rail mounting holes.
After making this first piece for the Z axis, I noticed it had a very slight warp to it. I don’t think it will be a problem, since I can lay the bar stock on a flat surface, coat the carriage with a thick epoxy, and lay it on top of the bar stock, so that the rail mounts will remain perfectly flat and in the same plane. The epoxy should take up any space due to the slight twist.
I now realize that I will need a perfectly flat work surface to make the remaining parts on. I also will need a perfectly flat base for the machine, so I decided to go ahead and build up the torsion box base at this point. The machine base will serve as my assembly table for the rest of the build.
To build a perfectly flat torsion box, you need to start with a perfectly flat surface. Inspired by this article on popularwoodworking.com, I made two small torsion box beams. This allowed me to practice the techniques for making a torsion box, and then I could use these to create a flat work surface for building the torsion box machine base. You will see later what I mean. Here is a picture of the two torsion box beams being constructed.