Without reading through this whole thread, has there been any discussion about how to properly and accurately locate holes, marks, or centerlines prior to drilling and tapping? I'm setting myself up to try some BruceBars, and realizing the level of accuracy required for machined parts is significantly tighter than that for wood.
Is it typical to locate and drill the bolt holes between the neck and body first, then inlay the bars into the neck to transfer the holes, before drilling and tapping? This seems like it would provide a more reliable result and eliminate a lot of potential sources of slop, VS trying to set up some kind of a jig to perfectly locate and drill holes at some pre-determined spacing before installing the bars into the neck and hoping everything just lines up the way it should.
Second question, is there any reason not to do a little taper / countersink with a slightly larger drill bit on the accepting thread hole of the BruceBar to help guide the bolt into the hole when installing neck to body?
Hey Nathan;
Those are good questions, directly related to Advanced Luthier Skills. In particular, how to locate neck bolt holes through the body, the neck and the BruceBars, getting them in the right place and all lined up with each other. Yes, there are some Old Machinist's Tricks which can help do that quickly and accurately.
Back in the pages of this thread, I went over the procedures for Spot Drilling and Machine Drilling. These are two basic techniques for accurately locating drilled holes in metal parts. Drilling holes right where you want them to be. Links to those posts below.
But that's assuming that you
know where you want them to be. Dimensions that you can measure and scribe lines to. But, where do you get those dimensions, particularly if you are trying to get holes in several parts to all line up together? The
correct way, if you are preparing for production, is to do some old-fashioned
engineering stuff. You know, thinking it all out carefully, measurements, drawings, checking them all against each other. Making sure that everything fits before you start doing any drilling. And then, using good technique to locate and drill the holes to those dimensions. That's a lot of work.
There's a shortcut, if you want to save some time on a one-off or prototype. It's called Match Drilling. Basically, you are locating and drilling the holes in each part separately, in a particular sequence, using the holes in the previous part to locate the holes in the next part. The sequence is important; you have to think ahead and decide where to start.
For the neck bolt problem, first take a look at the back of the body, the inside of the neck pocket, and the heel of the neck blank. Figure out approximately where you want the bolts to go. How many bolts, the pattern, the rough locations, etc. Consider how the bolts are arranged on the back of the body. The visual look, neck plate or ferrules, how close to the rounded edges, etc. Quickly mark the locations with a pencil.
Look inside the neck pocket, and do a visual check to see if those hole locations make sense within the pocket. Approximately, not too close to the edges. Then look at the neck heel. Will those holes and the bars fit into the heel, avoiding the truss rod and not too close to the sides?
If it all looks good and sensible, then you can start the Match Drilling. Mark and centerpunch the hole locations on the back side of the body. Then drill the holes through the body, into the neck pocket, using a small drill bit. Preferably in a drill press to make sure they are square. I usually use a 1/8" bit for this. It works well as a pilot hole for the larger bits. And if you screw it up or change your mind, it's easy to glue in an 1/8" dowel and try again. Check the inside of the neck pocket to make sure the hole locations still make sense.
Next, clamp the heel of the neck blank into the neck pocket. Position the clamp so it's not blocking the holes in the body. Check the alignment of the neck on the body, to make sure it's straight in relation to the body centerline. Put the 1/8" bit in a handheld drill motor. Insert it through the hole in the body, and drill a little bit into the neck blank. Not much, just enough to locate the hole. This spots the hole in the neck exactly in line with the hole in the body.
Unclamp the neck and take it over to the drill press. Use the same 1/8" bit to drill the holes all the way through the neck blank. This transfers the holes to the top surface of the neck blank.
Now, rout the slots for the BruceBars. Locate your routing template on the top surface of the neck, centered on the 1/8" holes.
Cut the brass stock for the bars, round the ends, and test fit them in the neck blank. With the bars in the slots, flip the neck blank over and put it back in the drill press. Use the 1/8" bit again, down through the holes in the neck, to make small spots in the bars. Before pulling the bars back out, mark them so you know which is which and which way they go. They are now Match Fitted to the neck and body, and they have to go back in the same way.
Put the bars in a vise and use the Spot Drilling technique to drill the holes through the brass, tap the threads, and put a light countersink on the bottom side.
Enlarge the holes in the neck to a size that clears the diameter of the bolts. A brad point bit will follow the 1/8" pilot hole nicely. Drill from the bottom surface, so that any splintering out will happen inside the bar slot.
On the body, finish the details on the back side. If you are going to use ferrules under the bolt heads, use a Forstner bit to drill the counterbores, centering it on the 1/8" pilot holes. If you are using a recessed neck plate, align the routing template around the pilot holes, and rout the recess. When that's all done and good, enlarge the pilot holes to bolt-clearance size with the brad point bit.
That's it. The trick of Match Drilling is using small size pilot holes in sequence to locate and drill each other. That gets everything aligned. Then each part gets enlarged and finished.
Note: If you want to, you can do the Match Drilling sequence in the opposite direction. Start by making the bars with 1/8" pilot holes in them. Rout the bar slots in the neck. Position the bars in the slots and use the pilot holes to drill the pilot holes in the neck. Then clamp the neck in the body and drill all the way down through the bars, the neck and the body. Then finish all the holes. The point again is that the pilot holes are setting the alignment.
Okay, let's talk about drilling methods. Specifically, how to drill holes in accurate positions in metal blocks. Which eventually become hardware for basses. I think every piece of custom hardware we make has holes in it. And they usually need to be in fairly precise locations to line up with other stuff.
There are two basic ways to drill a hole in a specific location. I call them Spot Drilling and Machine Drilling.
Spot Drilling:
In Spot Drilling, you start out by making a small cone-shaped indentation in the metal, called a Spot, at the precise location where you want the hole to be...
Spot Drilling:
Here's a closer look at the technique of Spot Drilling. This is the method used to locate a hole in a metal part, accurately, using hand tools and a drill press. We use it for making one-offs or a few parts, where we don't want to take the time to set up for Machine Drilling. Machine Drilling is used when you need to drill holes in accurate locations in a batch of identical parts. But setting up for Machine Drilling usually requires the use of a Master part. I'll explain that as we get into Machine Drilling. And that Master part is usually made by.....Spot Drilling.
The...
) but taking a closwer look now at what I ordered, it looks like the marks only go down to 1/16 of an inch 
. Oh well, still an upgrade over the hand-me-down from my dad that I've been using for the last 20 years.
