My general practice has been to taper the bridge from the bass to the
treble, for example in a French double .75" to .675" down to .626" at the
treble, and I try to keep the same profile in the corresponding hitch-pin
molding from the back-pin / no back-pin break on up to the top, so the
hitch-pin molding at the top might be 5/16" to 3/8".   Down bearing is
really a guessing game, though one must be careful about not exerting too
much down bearing pressure on the bridge as this will tend to distort the S
B; the same thing holds true for side bearing. Think of it this way: the
back-pinned bass and tenor strings place little or no down bearing on the
bridge. From there to the top the down-bearing increases dramatically. The
way to deal with this is to taper the bridge to reduce down bearing
proportional to the profile height of the hitch pin molding. . So as
Hendrick says, "Moderation in all things" especially in down-bearing and
side-bearing.
Stepping off my rickety soap box,
dpj

On Tue, May 23, 2017 at 9:17 AM, Anne Acker <[log in to unmask]> wrote:

> I have worked on a number of instruments with this 'feature', and while
> they do require a bit more care in the set up, I have had no problem,
> including replacing the original low quality plastic jacks with Norm's
> excellent output.
>
> What I can say, is while the original builder experimented with this and
> various other ideas, the structural results of which have given me some
> interesting restoration/repair work testing my own understanding and
> skills, I can relay that the sound quality of the original builder's
> instruments is truly outstanding. In particular, the bass is tremendous,
> which was, I believe, one of his major goals in his experiments.
>
> As the instrument in question was used for concertizing extensively for
> decades by the previous owner, and will be by the new owner, I can also say
> that the result was reliable and very fine in all regards.
>
> It is interesting though, indeed!
>
> AA
>
> ----- Original Message -----
>
> From: "Hendrik Broekman" <[log in to unmask]>
> To: [log in to unmask]
> Sent: Monday, May 22, 2017 11:35:24 PM
> Subject: Re: Tapered nut - Why?
>
> > On May 22, 2017, at 8:38 PM, Norm Purdy <[log in to unmask]> wrote:
> >
> > A collegue of mine is rebuilding a double manual instrument (original
> builder will remain anonymous.) I've heard that sometimes the nut is
> tapered from bass to treble, and this is an extreme case. Can someone
> explain the theory behind tapering the nut? It seems to me that this serves
> no purpose. Of course, there is very good accoustical reason to taper the
> bridge, but the nut? The only effect I can see is to cause problems.
> Setting up new jacks must be a nightmare. The distance from the plectrum to
> the top of the jack will be different for each note unless the jack rail is
> tapered to match. Key dip would be difficult to get consistent, stagger
> will be hard to get uniform. All for no particular advantage that I can
> see. What am I missing?
>
> Here on planet Hendrik I find it easier to manage calculations (aka
> guestimations) of down bearing if the strings are kept nominally parallel
> to the soundboard (think planning the hitchpin rail moulding height,
> especially in the treble where a high nut would play hob). I also notice
> any number of classical instruments that display tapered nuts. Besides it
> just seems intellectually tidier to me. On the other hand, the “extreme”
> bit of your description is alarming. This is not a situation where, if one
> is good, two is better. Moderation in all things.
>
> There may be difficulties involved in setting up new (bottom screwless)
> jacks but they’re easily managed. I have a five rank installation staring
> me in the face but I’m not particularly worried. It’s just time. I have
> another 15-y/o (but otherwise identical) instrument back for resale and the
> original staggering persists.
>
> Best,
>
> Hendrik Broekman
>
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::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
Note:  opinions  expressed on HPSCHD-L are those of the  individual con-
tributors and not necessarily  those of the list owners  nor of the Uni-
versity of Iowa.  For a brief  summary of list  commands, send mail to
[log in to unmask]  saying  HELP .
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