I'm a big fan of stems.  I'm also a big fan of set-ups that are accurate, easy to adjust, leave plenty of room to work around, and are built to last.  This is one of my favorite fixtures I've come up with.  Having done a lot of research into versions people have come up with, I narrowed down my ideal form and got to work.  One of the big issues friends of mine told me about their fixtures is that they require a fixed width bar clamp.  Any variation and the fixture would not center the clamp on the bridge.  Some also complained about there being no support for the bridge itself.  The design I put together has an easily adjusted quill angle, adjustable offset bar-clamp tower, adjustable bridge length, and a bridge centering arm that helps keep things positioned under heat.  Recently I added gas vents to the bar-clamp top cap to help reduce it's heat sink qualities and to help expel fumes and expanding gas from inside the stem tubing. 

The frame is cut from 2" x 2" solid Aluminum, employs a Paragon Machine Works 7/8" tube block to brace the quill, Steel beams, and Stainless Steel hardware. 

bike, stem, fixture, jig, bike stem, quill The Bicycle Frame Fixture: The alter of frame builders, the critical space to establish the geometry of the frame and to hold it's elements in place for joining.  Thousands of iterations exist, here's what I came up with.