Step 8: Building the main triangle
The first joint that we'll tackle is the bottom bracket (BB) to seat tube (ST). Insert the ST into the BB, trace the profile and cope the tube. Set the jig up so the bottom bracket is bolted down and select the correct vee block for the ST diameter. Rough up the end of the tube with sandpaper and then Clean the joint of any contamination (oil, paint, etc...) with a solvent and rag. Flux the BB lug and tube end and re fit the tube into the BB. Place the ST in the vee block and use some safety wire to pin the tube in the vee. Double check everything and then solder the joint.
The next joint we'll do is the downtube (DT) to headtube (HT). Cope the joint and jig up the HT and DT and check that angle. Adjust it until it's close and solder the joint.
The DT to BB is the next joint. Consult your frame drawing and rough cut the DT about 3/4" too long. Insert it into the BB. Re-jig the HT so that it is parallel to the backplate (can be done using a square to measure each end of the HT) and trace the DT. Cope, clean, flux, jig and braze this joint.
On to the top tube (TT) to HT joint. This is done just like the DT to HT joint.
The last joint is the one that requires the most patience. Again, consult your drawing to determine the tube length and rough cut the tube a little long. Slip the TT-ST lug over the tube end being sure to align it with the TT - HT lug. This can be done by placing the assembly on a flat surface and rotating the lugs so that they are clocked correctly to one another. Trace and cope the tube end. At this point you should be able to slide the TT-HT lug, TT-ST lug and TT onto the HT and ST. Measure you angles, measure your lengths ensure the HT is parallel with the backplate and position vee blocks under the TT. Before we solder, there is one new step that we add. We need to drill a 1/16" hole in the HT along the centerline of the TT. This will be hidden under the lug and is used as an air escape hole during soldering. Clean and flux the joints and solder both lugs.
Congratulations, you've completed the front triangle!