Prepping for the Rear Trinagle

After a few days of truancy from Chris Beard Custom Cycles a concerted effort was required this evening to get back on track. The goal this evening was to construct the jig that is required to complete the rear triangle. As with many things a lot of work, almost 4 hours, went into producing something that looks very simple. The jig for the rear triangle is a little more complicated than the one that i produced for the front triangle as it requires the facility to adjust the height and separation of the rear drop outs (known as the 'Over Lock-nut Distance' or 'OLD') and the angle of the top tube, actually the top tube just needs to be level but in order to achieve this adjustability has to be built in.

I began the process by attempting to weld some box section to my table 69mm apart so that the bottom bracket, which has a width of 68mm can be clamped between them. Unfortunately i had run out of Argon for the MIG welder so instead used some of the bronze, that i have from when i was considering using bronze as the brazing alloy, to fillet braze them onto the jig. After this was done the outsides of the box section were cut away and a slot cut into the inside using a plasma cutter so that they can close in to clamp the BB shell using a length of threaded bar.
A lovely fillet braze:
I produced the part of the jig for the rear drop outs by brazing a piece of box section standing on its end to the brazing table and, using the plasma cutter, cut a wide long slot down both sides to allow a peace of threaded bar to go straight through and have both backwards & forwards plus up and down adjustability. To make sure that the nuts do not simple go through the slot I produced large washers from an off cut of box section:
The threaded bar has nuts either side of the vertical box setion tube to set the height and horizontal position of the drop outs and two nuts on either side to set the drop out spacing along with the angle of the dropouts. The height of the drop outs is very important becasue it sets the bottom bracket drop, although i am building a 'track bike' it will only be used on the road so i am building it with a standard BB drop for a road bike of 68mm, a true track bike has a smaller BB drop so that the pedals to not catch on the banked track:
Completed jig with tront triangle #1 in place to help with component positioning:The next task will be to cut the chain stays to length and then to braze the rear dropouts onto them before proceeding to the seat stays.