Rear wheel and rear disc brake mounts

I drilled the hole for the rear wheel in the 40x20 tubing using a cheap stepped cone drill.  This worked very well, much better than a standard drill which leaves a ragged hole in 1.5mm steel.  I have an M12 clearance, 17mm spacer inside the tube to prevent it being crushed when the wheel nut and bolt is tightened.

With the wheel fitted, I measured for the brake mount.  I made an IS caliper mount using information from this excellent site:

http://www.peterverdone.com/disc-brake-mounting-systems/

 Cutting out the recess where the caliper protrudes was the most challenging part of the build so far.  I couldn't get an angle grinder into the recess and a Dremel was too flimsy.  It took me a long time with a hacksaw and a file - the end result is functional but ugly.