We've been working a lot on our filing technique.
For the first month we've been learning techniques that will transfer to smaller parts, we've learned about materials, and we've dabbled with some of the tools. Well, maybe that's an understatement, we've been pretty busy. Long days all kind of blend into each other.
So far, there has been a big emphasis on understanding and achieving small tolerances, getting rid of burrs, and, well, filing. Tomorrow, though, we get turned loose on our first watch movement.
Above is an example of a filing exercise. This is a bench block. We start with brass stock and are given a blueprint. Armed with our files, drillbits (and a drill press), and a sharpening stone we craft our bench blocks with a tolerance of 0.1mm (which, in the watch world is still a large number).
This one called for a grain finish (achieved by use of the sharpening stone) which are those lines you see; it also called for curved ends which was kind of the crux of the assignment, since they had to be done with our file by hand. After you've gotten your shape, everything square and flat you've got to throw a 45º bevel on the edges and chamfer your holes finish and clean it, then hope you don't get any kind of scratch or oil from your fingers on the surface-because that'll cause it to oxidize/tarnish and you lose points for that.
The smallest hole on the bench block is 0.5mm which is drilled with a pretty small drill bit (duh), you may be able to deduce that this is a very delicate hole to drill. A handful of classmates experienced this tiny bit breaking off into their bench block. This is where alum and some water heated over an alcohol lamp comes in. The reaction between the alum water and the iron based drill bit will dissolve the bit but leave the brass bench block (say that 5 times fast) unharmed.
The alum and water trick is one many of us will use down the road when trying to remove broken screws/stems/whatever from watch components. And it leads to this point, we're given these tasks with not always the most optimal tools, but the tools we are given are the tools that will prepare us for watches.