Another bridge pin angle question

[George Roberts]

This is the bridge from the parlor guitar that has the unreadable writing inside.  The front of the bridge, in front of the saddle, split off and I'm trying to duplicate the old bridge.  I am using the holes in the bottom of the bridge to locate the new holes, so they line up with the top.  The problem is that the holes are angled back at about 15 degrees.  Any suggestions as to how to drill the holes at that angle?  I can make a 15 degree wedge, but the drill is still going to hit at the circumference of the bit first.  A series of small pilot holes?  Thanks for the help.

[Andrew]

Dont mess around with trying to coax the drill bit into doing what you want - thats pretty stopgap and for this kind of purpose the results are almost guaranteed to be less than satisfactory and definitely less than ideal. I would most likely reproduce the hole locations by measuring and marking in this case, referencing common points to the centre line and an x - axis. Gluing the old bridge back together accurately will make finding common reference points easier. You could then drill the holes on a drill press prior to installation, if the angle of the holes is actually consistent, or if your hand and eye are good you could do it free hand. When in doubt, make trial replicas to test/practise out of scrap wood; ideally something with similar density and grain structure (i.e. spruce or oak will do quite different things when you mark and drill compared to ebony or rosewood, whereas a hard chunk of maple would respond more closely.

edit - you could also transfer the hole locations from the existing bridge, and then either measure or do the math to find the amount you need to move the centre points of the holes back by. Probably somewhere in the neighbourhood of .75 mm.

[Andrew]

2nd edit didnt seem to work. I may have misunderstood the nature of your query..

A good quality brad point bit (I like the lipped hss bits lee valley sells) and a drill press/chuck with minimal runout should solve any issue of bit-wandering so you could drill the hole cleanly in one step. In any case, make sure to account for the difference in location caused by transferring through the angled holes of the old bridge.

[George Roberts]

Hey Andrew,

Thanks for the help.  I'm glad I didn't rush into this.  You got me thinking more about the location of the holes.  I was using the bridge to trace the location of the pins, but then realized that would be like a mirror image of the location.  It turns out that one of the pyramid wings is longer than the other, and the mirror image approach would have doubled the distance the holes would be off.  I'm going to use the direct measurements.

I have a set of the Lee Valley brad point drills, and checking them with the 15 degree wedge, the brad point engages before the lipped edges.

[Andrew]

Glad to be of service :)