Gearchange shafts are hard to come by but I spotted a replacement shaft sold by Draganfly in UK. Good value so ordered one and prepared shaft. I measured the shaftlength before I cut off the piece to be replaced (57mm). When it was cut I noticed that it was slightly off-centre as you can see in top pic. I measured a few disecting lines across it and then centre punched the centre of the shaft to be replaced. To retain some strength in the boss that holds the shaft I decided to only drill in 3/4 of the way. The supplied shaft was an inch overlength so you can decide wherever you want to drill to. I drilled a small pilot hole after setting up the piece in pillar drill and then drilled in with a 12.5mm drill bit to the appropropriate depth. Once drilled I checked the depth again and then measured the shaft length I needed, cutting off the excess. It was just a case of then using the vice to push the two pieces together to give me the finished shaft. I am going to have one trial fit with cases just to make sure but then just braze the join and a new gearchange for 1/4 of what a good one would cost.
Just as well I tried it assembled with cases. If you notice the larger cutaway for the tightening bolt in the new shaft, this meant that for there to be adequate spline length available outside of the case for the gearlever to catch the inner splines the shaft had to lengthened by 2mm more. This was easy with a tap of a hammer, but it would have been a messy job if already brazed. Happy enough with shaft now, span it in a drill slowly to check alignment along its length and will braze it together now.