Bridge Pin Marking and Drilling 2023-11

This operation is documented on two pianos, a Steinway L and a Steinway O. Work is guided by shop owner Mr. Jude Reveley at Absolute Piano Restoration. Before working on bridge, the plate is clamped at ideal position. Normally 2 clamps are enough. The pinblock is being glued down under plate, thus many clamps here.

First, track of center string on each note is marked on bridge. Ideally, this track will be the location of middle bridge pins for the note. At V-bar section, run a thick mylar strip from the right side of middle tuning pin of a note to the hitch pin where the center string loops. A magnet is used to stable tuning pin end of mylar. Use a bright colored pencil to mark on bridge along the mylar strip. Note, each center string looping location at hitch pin is marked with black marker. The colored pencil dulls easily. Sharpen it along the way.

At agraffe section of tri-cords, place front side of string, fish line here, at the center hole on agraffes. Our little spring clamp has a small pointy nail inside, which goes into agraffe hole. Put the point in the center hole. Run string to it's loop mark at hitch pin, place a transparent ruler next to string, loosen string, mark string track on bridge.

For bi-cord, without advice from shop owner, I placed the pin on mini clamp in between two holes on agraffe, then ran string in between two hitch pins of the note, marked track between two bass strings of the same note. Of course sharpen pencil along the way for accuracy.

For uni-cords or single bass strings, poke the pin in clamp right into the agraffe hole, run string on top center of hitch pin, mark string track.

These are the marks of string tracks on bass bridge. According to advice from Jude, each bi-cord string needs to be marked, as well, so we know exactly how the string spacing looks like.

Now, place clamp at each hole on agraffes, run string over the top center of the hitch pin for that string, mark string track with a different color to distinguish from red center line. Check markings on the two bridges before putting tools away.

The string tracks don't look evenly spaced. So the next step is to evenly space the notes. It is cosmetic, but will make final stringing result even and look professional.  A ruler and a square are used here to measure distance between end notes in each section. The distance reads 211mm. There are 17 notes in this section, thus 16 spaces in between. About 13.2mm space is needed between notes. I mark the spacing with a ruler, draw the ideal string track parallel to the red line using regular pencil. Then check spacing by eye.

The shop owner comes in with his tool of accuracy. Each square is made of two pieces of metal gliding against each other for adjustable width, fastened by screw(s). He sets the gauge to calculated width, marks ideal spacing with this tool. It is much more efficient and precise than trying to read the ruler for each note space.

Comparing the red (ideal) and charcoal (spaced) marks, they are very close to or on each other. This means we are doing well here. At the tenor section, the note spacing fans out or increase and decrease gradually. Mark accordingly. Here I think it would be better to mark the original bridge pattern first to be a solid reference. When marking the fanning spacing at tenor without reference, there is too much guess work.

Again, the original bridge pattern is better marked before all steps above, according to shop owner. Try to do better next time. On bass bridge, all bridge pin holes must be transferred. On treble bridge, only middle bridge pin holes in front and back rolls are needed.

Well, I marked all holes before the shop owner said only middle ones were needed. Note that the original pattern at treble section is off centered. This may have been an attempt to avoid string rubbing plate strut on the bass side of the section. So let's put in the plate and check. The middle picture shows loop of the very left string at original bridge pin location, 2mm from strut. The right picture shows the same string at ideal bridge pin location, 1mm from strut. We have room. The plate may be ground down a little to make room for this string.

We decide to use the speaking length, or front pin line, from the original bridge pattern. Pictures show our homemade bridge pin from to back spacing jig, from 15mm to 20mm. On treble bridge, observe the width of each note from treble to bass. mark where to change to a larger width jig. Align the inside edge of jig with the middle front bridge pin mark, align the 2 pencil marks on jig with ideal string track, mark for front and back bridge pins. Only two lines are needed for each note. Location of each pin will be marked later.

On bass bridge, at uni-cords, the shop owner makes front and back bridge pins same distance to closest edge. He uses fingers as guide to draw pencil line. Then a marking jig is used to scrape the lines. Where the scraped line and string track crosses is where the bridge pin goes.

For bi-cords, again, he makes sure front pins to bridge front edge is the same with the back side, using his finger as guide to mark where the speaking length starts. Where his pencil mark meets string track line is where the center point between two strings is. The homemade note width jig is used here to mark where front and back bridge pins go.

To mark for each bridge pin, we use homemade punches with different spacing between pins. Check punches with bridge pattern, choose which one to use for the section accordingly. Mark front pins first. Align the horizontal holes on plastic gauge with the pencil line, align the center vertical line with string track, whack the punch hard to transfer punch mark. For the back pins, take a look at the picture on the right, find the horizontal laser mark of the correct front to back distance, align with front pin punch mark, align the center vertical line with string track, whack the punch.

On bass bridge, the shop owner checks distance between strings of each note, places bi-cord gauge against original pattern, and picks holes by original string spacing. Same procedure with treble bridge, align horizontal lines with front pin line, align center vertical line with middle line of string tracks, whack the jig. The back pin marks use the same method above.

For uni-cords, the front pins are marked where two lines cross each other. The back pins are not. Jude points out that the bass strings are very thick, a little off set at the back bridge pins will allow a smooth angle for strings to weave through. Align the left vertical line on uni-cord gauge to the string track, place punch in gauge hole, whack it.

After marking everything, check both bridges for uneven marks and missing notes. deepen all marks for drill bits to bite on.

Before drilling, lay down old bridge top as reference. Pay attention to which direction the pin goes. Mark where to lean the drill bits so two holes won't run into each other. Test drill bit and drilling depth on a scrap piece of hard wood before hand. When the bridge pin is bottom up in the hole, there shall be about 3mm sticking out, according to the shop owner.

The drilling jig is also homemade, the level shows a 17 degree drilling angle. During drilling process, constantly blow clean drill bit slot to remove built up dirt and gum. Sometimes a thin wire is needed to loosen all the goo. Drill at middle speed. Too fast may cause the drill bit to heat up and break.

Always check for missing holes before tools are put away. Plug bridge locator holes with toothpicks. Now the bridge top can be sanded for next steps. Many thanks to Mr. Jude Reveley, our dear boss, who guides us through every little detail with great patience. Many thanks to Mr. David Betts who's spirit is always around supporting me through difficulties.