I'm making a stem for the project that I'm currently working on, and I realized that I've never put up a blog post detailing the process of building one. Making a stem is (obviously) not nearly as complicated as making a full bike frame or even a rack (really, it only has two joints...). But it does still require quite a bit of doing to make it happen.
This one is to have a 100mm extension with a 0 deg. rise, 1.125" steerer clamp and for a 31.8mm handlebar. I'm fillet brazing it (to match the frame) and using clampy bits from Paragon Machine Works. I usually make my own clamps for stems but the frameset is going to be using distinctive PMW dropouts, so the PMW stem bits seemed to fit aesthetically with the rest of it.
I don't use a stem fixture when I make stems. I don't make nearly enough of these things to justify the expense of buying or making a fixture. Which is not to say in anyway that a stem built without a fixture is at all less straight than one built with. Fixtures in general are a time saving device. They tend to hold things in generally the correct relationship to each other so that when you attach them they (hopefully) remain in the correct relationship to each other. You can definitely get the same results with lots and lots of careful measuring. You really do need to check everything for squareness anyway, even with a fixture.
(As a note, it's perfectly possible to make an entire bike frame without a frame fixture. It just takes more time. This was actually a totally acceptable way of making custom bike in the past. "Free building" as it's know, can produce very similar results to building with a fixture and some builders still use this method. The main disadvantage is that it involves drastically more measuring and double checking of things to maintain straightness.)
The real star of the show here is the tubing block that hold the extension during mitering. This little beauty enables me to cope both ends of the tube perfectly in phase with each other. If I wasn't able to do this everything would be a lot more of a pain in the ass. The majority of the time I spent on this so far was measuring the squareness of the cuts to the reference of the tube block. After that everything else was pretty easy. Just tacking on the clamps and double checking the squareness (everything was spot on). Then filleting it all together. All that's really left is to do the finish work.