Here's a quick-n-dirty
© Frank Ford, 2007; Photos by FF
This is the kind of job I find myself doing from time to time when we need a special wood drill bit for the repair shop at Gryphon. One of the guys was getting ready to install a new bridge on a solid body electric guitar, and he needed to drill two 9.0 millimeter hole to press fit the special bushings.
Because this was to be a quick job, I thought I'd time it. . .
I mounted a piece of 3/8" diameter W-1 drill rod in the lathe collet, and turned about an inch of length down to nine milimeters, or 0.354"
At the end of the rod, I dished out a bit of it, leaving a sharp rim and a little point in the center:
Both features will serve to center and stabilize the bit as it starts into hardwood.
Here, I have the turned rod mounted in a collet block in the mill vise, and I'm making a couple of cutting lips, with a 90-degree cutting angle:
Back on the lathe, I turned the shank down to about 5/16" to provide chip clearance and to avoid having the cutter rub too much in the hole:
I used a flat file to provide a bit of clearance on the perimeter of the cutting faces:
And a carbide disc in my Foredom tool to cut relief behind the bottom of each cutting lip:
I didn't measure any of the angles or amount of relief - I just wanted some clearance and relief. I wasn't making this tool for sale or heavy long term use. In fact, it might be a one-use thing for all I know at this point.
Next, it was time to harden the cutting edges. I stuck the bit in the propane flame until it was nice a bright red-yellow:
A quick dip in the pool:
And my cutter was basically done.
A diamond pocket hone and a few strokes to hone the cutting edges completed the job:
Hey, it's ugly, and ill tempered, but it's ready to cut:
That's right - I did nothing at all to temper the hardened bit. So what if it's brittle? We'll use it on wood, and we'll hardly test its resilience that way.
Here's a first test cut in a piece of maple die board:
A nice flat bottom hole:
Oh, and the entire job took 47 minutes, start to finish, including setting up the photo shots:
That's just short of the time it would take to drive to the Woodcraft store and buy a bit, if they have such a thing in stock.
Back at the guitar repair shop, the job went well, with no chipping of the finish:
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