Just getting into CNC work, so this is all new to me. Decided to build the top for my Sience Labs 30" Longmill by creating a 4' X 4' X 5 1/4" thick torsion box.

The gridwork is made from 5/8" MDF, saddle jointed together. I himmed and hawwed over whether to glue the saddle joints together or not, as I was concered about the tight joints swelling during assembly, and making it very difficult to close the 8 separate joints in each row together without having to beat them to death to close them. In the end I decided to fit them dry, but glued and screwed the rim pieces (which were also dado'd) as well as the top and bottom panels, which I felt would provide the needed rigidy.

The top and bottom pieces were 3/4" MDF, which were biscuit'd to the rims using #20 biscuits. Knowing from experience how dry MDF is, I used watered-down PVA glue to preseal the gridwork prior to glueing the top and bottom pieces on. (I used a foam roller to apply this thinned glue). Once dry, I started by glueing the biscuits into the rim pieces, then applied a healthy bead of Titebond III to the gridwork and to the biscuit slots in the underside of the bottom panel. I flipped the assembly over, and moving as quickly as I could, repeated the same assembly steps I'd followed for the bottom panel.

I clamped the entire assembly onto my extremely flat assembly table (which is also an MDF torsion box) and weighed down the centre sections using 320 lbs of 1 gallon cans of finish that I had on hand. Yes, I know I could have made clamping cauls, but the finish tins were handy, so I went with them.

Of course, the proof is in the pudding, so this morning after I removed the clamps and weights, I checked the torsion box for flatness using my 36" Veritas straightedge (accurate to within .0015" over its length). I was really happy with how flat it was, and how rigid it is.

Now, as soon as my friend has the 2" box steel supporting framework welded up, I'll get to work assembling my CNC!

01 Saddle joint dadoes completed.JPG 02 Assembly phase 1 underway.JPG 03 Closeup showing joints.JPG09 Glue applied.JPG10 Rim piece clamped into position.JPG07 Corner block being glued in.JPG11 Faces glued on and clamped.JPG14 Dead flat.JPG

I am having a friend weld up the supporting frame of 2" box steel tube.