Official Luthiers Forum!

I realize I've always (this will only be my third build,) had some trouble drilling bridge pin hole without the bit not starting exactly on my mark. The bridge is glued on to the top.
This being a 12 string I am even more concerned. I have tried things like starting with a .062 drill first & then enlarging with mixed results. I am thinki9ng about that drill, it looks like a countersink/pilot they use on metal lathes, is it called a center drill?
please advise.

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Mike McNerney

Are you using a drill press or a hand drill?

i dont think i can get close enough with drill press o electric or old fashioned egg beater

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Mike McNerney

no i cam do it on the press

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Mike McNerney

If you haven't tried it on the press then you definitely should. Even a cheap drill press will be more accurate than just your hands.

Also have you tried a brad point bit? If you use a regular twist drill bit they can wander a little bit.

I would recommend drilling first then gluing on the bridge especially if you have a drill press. In any case I use a very sharp pointed awl to mark out the center points with a light touch at first push a point into the wood and then measure everything till it's perfect then with the awl push in really good to make a nice deep mark. Then use brad point drill bits.

Like these:

https://www.stewmac.com/Luthier_Tools/T ... gJM7PD_BwE

ok brad drills in the press

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Mike McNerney

I use this, both for drilling bridge pin holes with brad point drills (tapered shim pieces each side to slant holes) string holes for classical bridges, and have also made jigs using it, e.g. for tuner hole drilling guides (paddle head and slot head), neck bolt holes, etc.
150mm x 100mm travel, divisions on scale are 0.03mm, 0.0012 thou so pretty accurate.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Brad point bit for sure. I'd recommend getting 2mm for side dots, 3/16" for bridge pin holes, and 1/4" for tuner holes. Don't scrimp on cost, these are one kind of tool where quality makes all the difference (reamers are another). LMI has good ones available individually.

2mm brad points are difficult to source, took me some time to find a supplier. Bosch make them.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I'm missing something. A bridge is glued to the top. It's got six (or seven or twelve) 3/16" holes drilled for the bridge pins. Sounds to me as if the drill pilot holes now exist, they're pre-drilled in the bridge, and all that remains is drilling through the holes in the bridge through the top and bridgeplate. I've done this several times with no problems that I've seen.

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Peter Havriluk

i glued the bridge on without the pilot holes drilled

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Mike McNerney

I would probably remove the bridge, drill the holes, clean everything up, and re-install the bridge.
It is hard enough to drill accurate holes, in a 6 string bridge, with the bridge off, using a drill press, and a quality brad point bit. I would not want to try it with a hand drill, after the bridge is on the guitar. And, then add in, IT'S A 12 STRING!!

If you are faced with drilling the holes with the bridge already glued on, I would do what jfmckenna suggested above:
"use a very sharp pointed awl to mark out the center points with a light touch at first push a point into the wood and then measure everything till it's perfect then with the awl push in really good to make a nice deep mark. Then use brad point drill bits."

If you have a good sharp brad point bit and the center points well marked with an awl (or the tip of the brad point bit if you don't have an awl), you could drill them pretty accurately with a hand drill. I've found for freehand drilling that you can improve the ability of the awl marks to keep the bit on target by twisting the brad point bit by hand in the awl mark and pressing down to make the mark deeper and take on the same shape as the brad on the tip of the bit. Then put the bit in the drill and drill the hole.

For the future, drilling the holes on a drill press before gluing the bridge on is a simple way to get dead accurate hole positions. The wood block behind the bridge blank in the photo serves as a fence that gaurantees that the pin holes get drilled in a straight line.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Check out this thread. I did a post on the Tony Karol jig. It is ingenious, simple, and extremely accurate with a drill press and brad point bit. I have used it for many years. Drilling the holes parallel to the saddle slot is a good thing.

viewtopic.php?f=10101&t=37702&p=494106&hilit=Karol+bridge+pin+holes#p494106

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It's not what you don't know that hurts you, it's what you do know that's wrong.

As the bridge is glued on, marking, awl, and hand drilling is perfectly do-able.
I would just add that if any of the hole's spacings are slightly out, you can compensate when reaming out the taper, certainly with the SM reamers which cut on one side
Keep the initial hole to the minimum diameter of the reamer (0.152, 3.8mm) and you can move it up to about a millimetre, should be plenty of adjustment there.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Make a jig that fits over the bridge that has hole guides.

As several others have said, use a brad point bit after you use an awl to start the hole. The awl of course is just the doing the same thing a center punch does on metal and if you're not using one then you should try it.

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Steve Smith
"Music is what feelings sound like"

One of those spring-loaded center punches like are used on metal is excellent for marking the holes in wood. Followed by a brad-point bit, it’s hard to screw up. (I put the brad point bit into the hole before I start the drill press.)

If all else fails follow your tagline - "consistency is the last refuge of the unimaginative"

I use a spring loaded punch to dimple the drill locations, then drill them with a tiny drill bit followed by a brad point.
If you really screw one up badly you can plug and redrill before you chamfer the holes. Most of the plug will probably be removed by the new hole and the rest hidden by the ball of the bridge pin sitting in the chamfer.
If the bridge is already glued on then trying to remove it would create another whole set of problems.

A 2mm bradpoint drill should be easy for you to find, you're in Ottawa the home of Lee Valley Tools. They should have almost anything you need.

Brent

A few years ago i bought the Starrett scribe to use for guitars only & that is my layout tool & I have one of those spring load things too so I'll work on some scrap first. i have a collection of small brad drills along with the SM reamer so I should be fine. thanks all

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Mike McNerney

There's a useful old machinist's trick that might help. Drill small pilot holes and check the positions really carefully. Let's suppose that one hole is a bit too far to the left. Make a small notch on the right side of the hole, and drill it out using the next size of bit. The notch will tend to start the bit cutting on that side, and the center of the hole will have been moved a little in that direction. On metal you can move a hole about .005" to one side that way per step; maybe no so much in wood, but everything helps. Keep checking and work your way up.

This won't help with a glued Bridge... but the frustrating process of measuring, marking and drilling reliable and super-accurate ping holes got me to come up with something. Stole it from the furniture-making days when shelf pins had to be dead on, in four different places so the shelves didn't wobble. Anyhow, this is what I do:

First, I mark the low E with a sharp awl and use a 3/16" brad point bit to just drill that hole "free-hand" with a drill press (this isn't an actual bridge, it's my flush trim template):


Then I put a template on the bridge, locating with a brass pin. Now, My holes run parallel to the front edge of the bridge, but if you angle yours, mark it with an awl and use a brad point bit and hammer to really seat the high E string through the template, and then drill that on the press:


Finally, put another brass pin in and use the fence with the template to knock out the rest. Super accurate, and very fast... especially if your pins are parallel with the front of your bridge. Plus it only cost me a few dollars to make:


Hope that helps... or maybe inspires someone else to a new idea. I don't hate bridge pins any longer

Full Disclosure... since my bridges are very "organically shaped" I actually start the process by using that flush trim template and drilling the two E string holes in a square bridge blank. Then I trim it close with a band saw and flush trim with a large compression bit.

Once that is done, I just slap that template on and bang out the other four holes. The whole process takes about 15 minutes. Shaping the 3-dimensional curves is another matter: