This was gently bowed and all the edges rolled. Luckily it was guilliotined oversized. One edge and one end were hacksawed and filed straight with a right angle to give a reference later for assembly. The rest was only roughly hacksawed to about 3mm over size, and will be milled down after assembly.
The two end pieces are made from 20x6mm. As can be seen in the photo, I used tool blanks as stops in the standard four way tool post, and clamped the piece being cut with a second T-slot piece. Use a guage to get tool post set up square.
The three middle pieces are 36x6mm, but I had to mill them out of 40x6mm stock. For this a peice of 20x6mm was placed in the tool holder under the 40x6mm, to pack it up to a height where the 10mm end mill could mill the whole thickness in on pass. I found I could take 1mm cuts with the mini-mill at top speed in low gear.
The Headstock end of each T-slot Piece was milled square the same way. The other end was left rough, for milling after assembly.