Counterbore size for lock building

[Dale Halterman]

This winter I plan on taking the plunge into lock building with a siler flintlock kit, and the gentleman who provided me with the kit also gave me a copy of a magazine article by John Bivins on precision lock building.

In the article, John recommends buying a 1/4" counterbore with a .136 pilot for the screws that get installed in the bolster. He states that this will probably have to be custom made. When I look in the McMaster-Carr catalog, I find a machine screw counterbore with .241 body and .137 pilot, which looks like it should work.

So, which size is right? MCM-C does list one with a 1/4" body and 3/32" pilot. If I need the 1/4" size, any reason I can't drill the pilot undersized, use this counterbore, then open up the pilot hole?

Any thoughts appreciated.

Dale H

[halfmeasures]

any reason I can't drill the pilot undersized, use this counterbore, then open up the pilot hole?

I can't see why this wouldn't work just fine. What are the head and body diameters of your bolster screws? jim

[B.Habermehl]

I'm sure that it will due just fine. If you have any interference issues with the screw head just dress the head down abit. A file and a drill press comes readily to mind.

[Dale Halterman]

Thanks for the input, guys. Now, another question has occured to me.

At what speed should I run the counterbore in my drill press? I suspect it should be slower than a comparable sized twist bit.

Dale H

[P.W.Berkuta]

Counterbores & countersinks should be run slowly - 200 to 400 rpm and the pilot should be oiled or greased lightly.