Balance rail Mortise broach desc.

[Richard Brekne]

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Clark.. you couldnt get a picture of one of these and send it along
could you ??

Richard Brekne
I.C.P.T.G.  N.P.T.F.
Bergen, Norway

Clark wrote:

> I promised to describe the tool used at Hubbard Harpsichord used to
> make consistent balance rail mortises in keys.
>
> The tool is chucked into a drill press and used on pre-drilled
> keyplanks (in this case the center rail is drilled at the same time to
> assure spacing); however, the same tool could be used for individual
> keys or just for key button mouldings.
>
> The working end has parallel sides corresponding to the width of the
> desired mortise, also matching the hole drilled in the work. The
> profile, looking at one of the flat sides, is tapered according to the
> depth and length of the desired mortise, with a larger taper at the
> end (for keys so the base of the mortise flares at the balance pin
> hole). The tapered sides are filed into v-notches and honed so that a
> cutting edge is formed where they meet the parallel sides.
>
> The tool should be made of hardenable steel, either cylindrical or a
> shape that can be chucked, with a diameter that is at least as large
> as the necessary length of the mortise. Drill rod should come with
> instructions for hardening, but it is fairly easy to do with a propane
> torch and water (heat the sharp edges to a _straw color_, quench, then
> draw the hardness by heating to red..). Additionally, a chisel
> corresponding with the width of the mortise (or smaller) should be
> made or obtained to clean out the waste and ragged edges.
>
> I'll post the results.
>
> Clark

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