Mylar

[BobDavis88]

> Punch the marks with an awl
>  and drill for the pins. This will give you the proper sidebearing.
>  
>  I do not want to duplicate any 'mistakes' made during manufacture. 

We like a hybrid method which uses both pattern and thread. The thread method
keeps the side bearing under control, but the pattern can, in addition to
duplicating mistakes, point to places where the manufacturer made small
compromises to keep the unison (and hammer) spacing tidy. You can see this in
pianos of very good make. Small differences in side bearing are theoretically
to be avoided but practically not so bad, if kept reasonable (Don't ask). As
in most aspects of piano repair, small changes from what was there, toward an
ideal, can tidy things up. Large "corrections" can sometimes cause trouble
elsewhere, like in the action spacing. At least it's good to be on the lookout
for other effects of any "redesign" we do.

When we use the thread, we still punch with a three-pronged punch to keep the
unisons the same size, using the thread on only one of the wire paths in the
unison. Little differences in hitch pin placement and width and so on will
otherwise mess up the spacing of pins within the unison.

Bob Davis