|
 |
| Tele Tech Note 4 | MAY 2008 | FREE |
By Terry Downs
The standard Tele or Strat vintage tuners are generally 11/32" diameter. The Kluson tuners shown below are commonplace.
Some folks feel the need to upgrade to a tuner with a higher tuning ratio or one with locking features. Gotoh or Sperzel are some examples. Shown below are some locking Sperzels.
The Gotoh/Sperzel mounting diameters are 10mm, which will not fit in the existing mounting hole. So, you just get a 10mm or 13/32" bit and drill it out right? WRONG!! Slightly enlarging a large hole in hard woods using a twist bit is a nasty operation. If you do it with a hand drill, the twist bit locks into the hole and the RPM of the bit drives it down through the hole rapidly. This results in chipping wood on the exit of the bit. This could be mitigated by clamping down the neck to a sacrificial piece of wood to avoid breakout, but even that does not often work good. A drill press allows you to control the peck rate, but it is still a difficult and risky operation. A brad-point bit is useless because there is no center to start the point with.
Some folks remedy the situation by using a tapered reamer illustrated below. This is a safe solution, but you end up with a tapered hole. In order to get the hole big enough for the tuner to fit, the ends of the holes are quite large. That's not unacceptable, but I'm personally not very happy with the result. The cross-section show below may be somewhat exaggerated, depending your your reamer taper. The thinner the taper the better.
Many years ago, I was drilling some holes in an aluminum chassis to mount some electronic parts. I was using a twist bit. They came out really nasty and required a lot of deburring. A machinist buddy suggested I use step drills. I was a changed man!! The holes came out perfect. Here is an inexpensive set of step drills offered by Harbor Freight. (No affiliation)
This process drills the front and back of the headstock with the 13/32" step. Then, a brad point 10mm bit is used to drill out the inside of the wood. The concept is to counterbore the top and bottom of the hole at a slightly larger diameter than the final hole. The final drill can be pre-inserted into the counterbore before turning on the drill.
I purchased a 10mm step drill, and tried to drill out the middle with a 10mm bit, but the bit was uncomfortably tight. I didn't like the way the drill started. That's why I went with this approach.
Let's look at the sizes of things.
|
Dia |
Decimal |
Description |
|
11/32" |
0.34375" |
Original Kluson Diameter |
|
- |
0.390" |
Average of measurements on MIM and Sperzel tuners |
|
10mm
|
0.3937"
|
Suggested diameter for the after-market replacement tuners |
|
13/32" |
0.40625 |
Slightly larger suggested diameter for after-market replacement tuners |
|
7/16" |
0.4375 |
An unacceptably large option |
Drilling the counterbores at 13/32" leaves just enough slop for a 10mm bit to come in a drill it open.
Put masking tape around the step drill on the step just above the desired diameter. It will give a nice visual for how deep you are drilling.
Here is the setup. I have a piece of felt with a hole cut in the center. I clamp it to the drill press plate as shown. I do this so I won't hurt the finish of the neck. The step drill vibrates the material radially. It really protects the finish well, but it is difficult to clean the sawdust out of it.
Here is the counterbore operation using the step drill. Be careful to not drill the next largest step into the wood.
Here's what it looks like after the counterbore. Notice how the next largest step has made a nice chamfer/roundover as it has barely touched it.
I then clamp the headstock (using a rag on top) so the 10mm brad-point bit is down inside the counterbore. An additional clamp on the right side would be good as well. I make sure I can manually turn the brad-point bit inside the 13/32" counterbore with no resistance. I start the drill with the bit inside the counterbore, then drill out the center. A footswitch for the drill press is a handy thing to have too.
Here is the final result. This good photo shows the ring that shows the 13/32" counterbore is larger that 10mm. That's only a 6 mil ring (12 mils difference in diameter). It's amazing how noticeable it is.
If you could find a step drill that had enough length to drill halfway into the material, you could do it all with a counterbore. Just drill the front and the back. It's too bad the required diameter is not 3/8" or 7/16". This Harbor Freight step drill would be all one would need. If anyone finds a 10mm or 13/32" step drill that has enough length to get halfway through a headstock, let us know.
© 2008 Terry Downs Music™
