Getting the bass bar in the front of the instrument represents a significant milestone. It means that the hard work is over, and I can get on with the fine work of finishing the instrument.
Fitting a bass bar is a slow, quiet, and exacting process. My primary tool is a knife, which I use as both a cutting tool and a scraper. I brace the end of the bar between the front edge of the workbench and my chest so I can use both hands to control the knife angle and pressure. As the wood begins to develop the conforming shape of the inside of the front, I can feel it start to sit evenly in the middle, and then I can extend the form to either end.
When I was taught to fit a bass bar, I was instructed to work some "spring" into the shape so that, when one end was pressed against the front, the other end raised about three millimeters from the front at the other end. (Although the College of Furniture was an imperial institution, so the actual measurement was 1/8 inch.) That way, the bar would be glued into the front with some tension built into the joint. However, that was for a modern violin set-up, and when I began to make instruments with a historical set-up, I decided that such tension was a detriment to the structure. The instrument for historical performance should have no stress or tension, so I try to make all joints fit as precisely as possible so there is no such tension in the structure. My bass bars fit the front exactly.
My clamps are still the ones I made as a student in London. I have occasionally thought about redesigning and replacing them but have never gotten around to that task. These work, and sliding these onto the bar feel like slipping on a well-worn, familiar pair of shoes.