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Category Archives: Martin Style Pyramid Bridge
Back to the bridge where most of the action has been playing out this week.
In the post before the last two I attached the bridge. after completing that task I needed cut a saddle slot and then to put a 16″ radius on the bridge to match the fret board.
This is a piece of bone I fashioned into a saddle. I will use it to help me find the compensation I need for correct tone on the strings. That is to say when the string is tuned to pitch and you put your finger on the twelfth fret the note should be exactly one octave higher, not sharp or flat. Different string gauges reach their pitch at different string lengths. this is where the compensation comes in.
With the makeshift saddle in place I tune the string and find the spot where the twelfth is one octave higher. Then I mark the spot where the saddle sits.
Once I have done the high and low string I draw a line connecting the two points.
This is my two-bit jig that does the job right with a tester in place.
The cut was too wide so I dialed it in with a spacer and my drum sander; taking a little off the spacer then doing another test cut, etc. When I got it dialed in I was ready to do the cut on the real thing.
My jig in place with my Dremel tool fixed with a 1/16″ bit. When the jig was in place there was no play whatsoever and the Dremel tool is so lightweight I didn’t even have to clamp it.
The slot cut 6mm deep. A little difficult to see but there is a pencil mark to the height of the frets with a 16″ radius.
With the slot cut I was ready to take the bridge down to the pencil mark. I use a piece of a broken flat bastard (that I broke intentionally for stuff like this).
now that the bridge is down to the correct height and radius I can ream the holes to fit the pegs. Go slow and check often those reamers cut fast.
All the peg holes reamed to the correct diameter.
With the un-shaped saddle in place.
As a side not to any of you folks interested in doing break down furniture. The reamers I used do a wonderful for that. I used a small diameter reamer but Stu Mac sells a larger one also that I think would be quite appropriate for break down furniture.
There have been so many little jobs to complete once I got to the neck. A lot of them not necessarily related to woodworking and hence there has been a lot of schooling going on.
In the last four days I got two major tasks complete; making and installing the nut and installing the bridge. This means I am getting pretty darn close to completing.
This is a bone nut blank. Here I cut it to length with a hack saw.
Next I want to get that 16″ radius arc pencil mark on it.
To hog it off down to the line I took it over to my 12″ disc sander. Then I rounded over the back by hand and did some detail sanding to final shape.
Here I marked out the string spacing. The 1st and 6th are about 3mm from the edge.
Then I used a fine nut file to mark the grooves. Now they are still shallow and have room for adjusting the depth.
I drilled the peg holes according to the nut string spacing. I drilled with a 4mm bit as this is the smallest diameter on my pegs.
Next I line it up the distance with this jig I made. Flip the jig around and it measures from the 12 to the nut. From the nut to the saddle is about 2 times the distance from the nut to the 12th. I say about because different strings stretch a little differently making scale adjustment necessary.
Once I have placement figured out I drill down through the first and sixth peg holes. Well actually I drilled one first, anchored it and then drilled the second. Here you can see the bridge anchored in position.
Then I made a caul to fit over top the bridge. Two holes match the bridge so it can also be anchored down with the bridge when it is glued in position.
The other five holes drilled in the caul are for downward pressure in case there is any lifting. With 4mm wood anchors installed in the holes I can then screw 4mm screws into the caul applying downward pressure onto the bridge. This was not so necessary for the center but is recommended on the ends of the bridge.
After a few hours I removed the clamp.
Most of the books and online resources I read use C-clamps, etc for gluing on the bridge. I got the idea for this self-contained clamping device off of youtube. I thought it was brilliant and error free. And I can tell you it worked very well.
Been doing a little work here and there but haven’t completed anything full stage enough to post it. Except for what I got done today.
Started on the bridge the other day and finished it today.
The bridge is a Martin style pyramid bridge, which was the predecessor to what we see on most acoustic guitars today – the belly bridge. The pyramid bridge is called so because it has pyramids on each side of the bridge. While the pyramids are mostly aesthetic they do provide mass for the bridge when gluing it down to the body. This style of bridge was common on vintage style guitars that had smaller bodies and lighter strings.
Blank of ebony 6″ by 1″ by 7/16″. Here I am laying out the reference lines.
I actually put the cove cut on it before I took it to the table saw but here you can see me using my tenon jig for getting the angle cuts. I line it up by eye and dial it in with the screw adjustment on the jig.
A little sleight of hand to get that one cut I couldn’t do with my right tilt saw. I clamped it up and slowly did the cut from the back side of the saw. Also to do the inside angle once I had all the sides and front done I flipped the jig over to the right side of the blade and dialed in the screw adjustment slowly until the lines met up cleanly.
this is my setup on the router table for doing the cove cut. As I said the cove cut was done first before the angles. After the angles were cut I had to clean up the coves cuts a little.
Nice crisp lines.
The body is radiused so I had to sand the contour into the bridge. To do that I taped some paper down on top of the body and then some gum tape sandpaper on to the paper. I didn’t want to tape directly onto spruce.
Here you can see my detail sanders. Small blocks help to keep things manageable. And of course the 10mm dowel is excellent for the cove.
A close up of the pyramid and cove. You can also see I did a roundover on the leading edge of the bridge.
The finished bridge without bridge pin holes or cut saddle groove. It sits nicely on top of the contoured body.
I am not sure how close I am to replicating the original pyramid bridge as I have never seen one up close and don’t know the exact dimensions but I am pretty happy with how this one turned out.