Q for the Watchmakers on site.
I've been reading about Screwdrivers, mainly which ones are the best but stumbled onto a discussion in correctly 'dressing' the tips. One Watchmaker went as far as to have a set of screwdrivers dressed for one particular movement, which I found interesting.
Q: is there any preferable stone You use and which method to use in correctly dressing a Screwdriver tip?
We're attemting to 'fit' the tip to the screw slot without allowing it to bottom?
I use a hard Arkansas Stone and dress the tip at a sharp angle so as to only shape the very tip. I have a very old swiss and a very old french and they are both dressed this way. By dressing them in this manner you don't chew the tip up on the very tight screws.
John
George Daniels nails it, I think, in his discussion on screwdrivers and screws. In his book, 'Watchmaking' he eschews hollow ground screwdrivers, and explains how to dress a screwdriver and a screw. The screwdriver, to fit the slot properly, should NOT touch the bottom of the slot, rather, be wedged in the slot, to keep from sliding out. This is a very common problem, The highly polished screws used in some movts are by nature slippery, and the first thing many student watchmakers notice is how easy it is to suddenly have your screwdriver skate out of the slot at high speed, and scratch or damage neighbouring surfaces or components. The telltale screeching noise of this would usually raise the eyebrows of the professeur in the classroom, who would then fix you with the "dress your blade" look.
Screwdriver blades should not be dead hard, as they will chip easily. I find I am dressing my screwdrivers very regularly, and I use a two sided India stone with a sharpening roller. I use this same stone to dress my tweezers.
Mr Daniels further states that most screws are improperly made; he explains how to make one from scratch, and the slot in the head, he advises, should always be chamfered.
As far as 'best', it's all a matter of taste, but good screwdrivers are never cheap. I mainly use Bergeon, but I also have others sets, an AF, an Horotec, and a very old set of Bestfit screwdrivers. Each set is slightly different, and I have come to know which one works best in any given application. I could certainly see having a set for a particular movt, if the movt was high end or fine enough to warrant it.