A $10 packet of drill bits will make a half dozen counterbore bits.
To make a home made Corby/Loveless counterbore drill:
Chuck a drill bit the size of the Corby bolt head in a cordless drill.
Put a new 120 belt on the belt grinder, or use a dressed bench grinder with a fine stone ( belt grinder works much better). You can do the last little bit of reduction with a hand held coarse diamond stone or dressing stone, but just a belt will do it all nicely. A polished finish is not needed.
Turn the drill on to low speed and spray the end with dye-chem or blacken it with a sharpie. ( this helps see how much you are grinding)
Switch to high speed on the drill and put the last 1/2" or so of the bit against the belt/wheel and start reducing the diameter.
Go slow and check your progress regularly. The part being reduced is longer than needed, that is OK. I usually grind down about 1/2-3/4" of the bit, but any length that can be controlled well is fine. You want to grind down extra.
When the reduced section is the diameter of the Corby shank, stop.
Grind the tip back flat to leave a 1/4-3/8" extension.
You now have a drill bit the size of the Corby bolt head with a pilot the size of your Corby bolt shank.
To drill the seats:
The scales should be perfectly flat where they meet down the center, and have parallel outer sides. Tape them tightly together.
Drill the scales while taped together with a drill bit the size of the Corby shank. Drill all rivet holes at one time with this bit. I stick a matching size drill bit through the first hole after drilling it to assure the other holes stay aligned.
Take the scales apart ( mark the "inside" to make sure you don't accidentally flip one) and set on the drill press table ( a flat piece of scrap wood as a backer is needed).
Put in your counterbore bit and re-drill each hole by placing the guide portion of the bit exactly in each pre-drilled shank hole. Make sure alignment with the pre-drilled hole is accurate. Also, make sure your drill press table is at 90° to the bit in all directions.
Drill each hole to the desired depth. Leave at least 1/16" of undrilled shoulder, 1/8" is even better if you have enough room.
Before taking the scales apart, sand to shape and buff the front of the scales as desired for the knife.
TIP:
After drilling out all the shank holes in the taped together scales, I take them apart and mark the insides to prevent accidentally drilling one from the wrong side...don't ask why I now always do this
. Then I drill the seats on all holes of one scales. Next, I only drill out the front hole on the other scale. I put a Corby bolt in those mating holes and lock the scales together. That way I assure alignment with the rest of the holes as I drill the seats. Next, I drill the last hole, and stick a Corby bolt in as I finish it's seat. By putting a bolt in each hole as it is drilled errors are rare this way.
I made a 10"X10" block of hardwood with a 1/2" deep 1/4" wide groove milled both sides of the center of it for the Corby bolt heads to slide in . It has an un-milled 1" section in the center to back the hole currently being drilled out. This block was made smooth, flat, and has parallel sides by running it through a friends thickness sander, but any 4/4 or thicker wood from the lumber yard should work fine as-is.
I put this block on the drill press table as my backer when drilling the scales. Setting the scales on it with any already drilled Corby bolts in the slot makes drilling the other holes out easier.
It provides a great platform to drill out the seats with good accuracy. I just hold the scales down on it with one hand and drill the seats with the counterbore with my other hand on the drill press arm. I drill one side, put in that bolt, and move to the next hole....fast and accurate.
Now, I have to go sing the Easter cantata - Happy Easter guys.
