I put together my Half-A-Jig (tm) today. I'm using one piece of extruded aluminum from 80/20 and a couple of v-blocks designed for drilling tubes. One v-block is cut down to accommodate the lugs on the head tube, the points of which would otherwise keep the tube from lying flat.
The idea here is to help me align the head tube and seat tube so that they stay in plane, without spending $400 bucks and weeks on the materials to make a full jig. Basically, I wanted a bit flat metal bar, but I didn't want to deal with the issues involved in clamping a round tube to said bar. I had assumed that, in the process of getting it set up to work with the specific dimensions of my bike, I would have to shim things to get everything flat.
I was pleasantly surprised to find that the two tubes ended up perfectly in plane! I had a bit of wavering, but it was between exactly level and .1 degrees off... I think I'll live. I may add some simple pipe clamps to hold things down so that I can tilt the whole structure to make tacking easier.
First Silver Lug
I've decided to try my hand at doing lugs with silver. Silver melts at a lower temperature and has a bit more surface tension and a lower viscosity when melted. For these reasons, it can be a bit easier to work with than brass.
A practice joint mitered, lugged, fluxed, and ready to go!
Results: I burned some flux. Having worked with brass mostly before, this isn't super-surprising. Temperatures that would be fine with brass are way outside of the range that I should have the metal while working with silver. I need to train myself to keep the flame back and moving more. If I can spread the heat out more instead of focusing so much, I should be able to draw things through better.
When I cut it open, I found that things were fairly well filled in most places, but still had some voids that I wouldn't want in a finished product. I'm going to do some more practice with random pieces of tubing and see if I can get past that point before I use the rest of my practice lugs.