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Screwdriver Sharpening

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On 6/18/2018 at 12:16 PM, milotrain said:

Gunsmiths have run into this problem a lot because external screws are decorative.  In order to protect the top edge of the screw's groove you don't want a tapered screwdriver or a hollow ground screwdriver you want a parallel ground screwdriver.  At the size you guys are working with this may be a moot point as Deggsie has said but it's valuable to know what you are going after.  Tapered and even hollow ground screw drivers can engage the top or leading edge of the notch which is it's weakest point, this is what causes deformation of the screw notch.  Ideally you want to engage the whole slot, or the base of the slot, not the top edge.

100% agree....but in the common vernacular, hollow ground is used to describe the resulting parallel, and desired, end you describe- i.e. the curve is a hollow vs the flat side of a regular screw driver.  Its what Wheeler and Brownels call them (this the set I have, and recommend it)  https://www.btibrands.com/product/professional-gunsmithing-screwdriver-set-89-pc/

I've do a lot of work on old machines and lathes (Schaublin 70's, Holbrook B8, rivett 608 etc) and a lot of these are put together with slotted head fasteners; some predate socket head cap screws.  Its really a shame to some of the nicest machines man's ever made scarred because some hack took a screw driver to them.  The trick is one  of those large gunsmith screw driver kits with hollow ground blades of different widths and thicknesses.  For stubborn ones you can put a wrench on the bit and it loosens without damaging the screw heat

Having said all that, I haven't weighed in on watch screws as (from lack of experience with watches specifically) I'm not sure of the necessity as it may be that the torque/contact ratios are different such its not required, and secondly the world best makers of watchmakers tools don't bother (although Bergeon does offer hollow grinding rig irrc) nor do many watchmakers who I view as highly competent.   I've a lot of books on watchmaking and cant' recall reading it (at least that I remember).  You'd think if it was important, given screwdrivers are the most used tool in this craft, tied maybe with tweezers, that if it was oh so important, hollow grinding them would be the first chapter in every book, yet it seems rarely or never mentioned.

bit of a zombie post.....didn't realize how old that one was :)






Edited by measuretwice

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Hollow ground screwdrivers are really only of use if you work on the same model of watch all the time.

The reason is if your flat ground screwdriver is too thin you just stone a tiny bit off the end to make it fatter.

On a hollow ground screwdriver you need to remove a lot more material to make it fatter, and then hollow grind it again to suit the screw you want to undo, so its harder to swap between brands of watches that you need to adjust your screwdrivers for.

If you worked as an 'in house' watch repairer of an expensive brand of watches, and always did the same movements then hollow ground is the best, but for most of us that works on what ever watch comes our way the flat ground is best being a compromise between time taken to reshape screwedrivers and the risk to 'chewing' screws.

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