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HPSCHD-L  April 2017

HPSCHD-L April 2017

Subject:

Re: When to Drill Bridge Pins Holes?

From:

Peter Bavington <[log in to unmask]>

Reply-To:

[log in to unmask]

Date:

Sat, 15 Apr 2017 16:20:49 +0100

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (99 lines)

Phillip Allen asked:

> Should I transfer the location of the bridge pins directly from the diagram
> before I screw/glue the bridge to the sound board?  Or should I affix the
> bridge to the sound-board, glue the sound board in place and then drill the
> bridge pin holes aligning them with the hitch pins so I guarantee that the
> strings are all perfectly parallel?

Different makers approach this in different ways. I prefer to set out, 
drill and pin the bridge pins with the soundboard out of the instrument. 
The hitch-pins must be in place first.

The first step is to glue the bridge on to the soundboard. You can 
position it according to the drawing. An alternative, more historical, 
method is to lay the soundboard in the instrument and stretch carpet 
threads along the lines of the front string of each C, measuring the 
required sounding length from the tangent position and marking with a 
sharp point on to the soundboard the place where these strings should 
cross the bridge. If you use this method, you must position the actual 
bridge some 2 mm to the left, to allow for the fact that the bridge pin 
in each case will be somewhat to the right of the left edge of the bridge.

Prepare the bridge and slope the sides as required, but at this stage 
leave a flat top surface to the bridge: in due course this will be 
bevelled, but I suggest this is best done after the bridge has been 
fixed and the bridge pins laid out and drilled (but not pinned).

Place the bridge on to the soundboard and push in ordinary sewing pins - 
probably about six are sufficient - to ensure that it will be stuck on 
in the right position and will not move around under the cramp pressure 
when glue is applied. The pins can be cut quite short after they have 
been driven in, to allow free rein to the cramps or go-bars or whatever 
you propose to use.

Then stick on the bridge. The top flat edge helps cramping it.

The next stage is to fix the bridge-pin positions. Draw or scribe a line 
along the top surface where the pins are to go. Lay the soundboard, now 
with bridge attached, back in the instrument and check with threads the 
maximum possible forward position of the bottom pin and the maximum 
possible backward position of the top pin (both these for 'safety'); and 
then mark with a point or pencil the desired position of the c2 and c1 
front strings.

I next make a kind of T-square, with a slip of mylar attached to one 
edge of the long arm, upon which I have marked as accurately as possible 
the positions of the bridge pins. This will be run along the back edge 
of the soundboard, with the long arm of the T extending perpendicularly 
across it, and each point where the mark on the mylar meets the line on 
the top of the bridge will be marked to be drilled for a pin.

The actual spacing can be derived from the drawing by running the mylar 
in a similar way across it. Alternatively, you can derive it from first 
principles. Generally the spacings run in groups of six notes or an 
octave, with the pins being further apart as you descend the compass. 
Bear in mind that the bridge-pin positions, measured perpendicularly, 
need to be further apart the more oblique the slope of the bridge, 
otherwise the strings will bunch up - though sometimes this is a 
deliberate feature of the design. Sometimes the strings of each course 
are closer together than they are to the neighbouring courses; 
sometimes, on the other hand, all the strings are equally spaced.

It is not important that the strings are 'perfectly parallel'. More 
important is that you produce the correct sounding lengths for each 
note, though even here some small inaccuracies probably do not matter 
too much.

Check visually that it looks regular and logical. Check again that, with 
the layout you have marked, there will be room for the top and bottom 
strings. Pop-mark the bridge positions and drill; then produce the bevel 
on the left edge of the bridge with a plane, fingerplane, and/or scraper.

Does all this make sense? I hope so. It is easier to do than to describe.

Peter
-- 
Peter Bavington
Keyword Press
291 Sprowston Mews
LONDON
E7 9AE
United Kingdom
www.keyword-press.co.uk
Tel.: +44 (0)20 8519 1170

-- 
Peter Bavington
Clavichord Maker
291 Sprowston Mews
LONDON
E7 9AE
www.peter-bavington.co.uk

::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
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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