>John..... you are in agreement with my thoughts here. There are many >variables as to the answers and among them are, speed of drilling (not >only rotational >speed but vertical penetration speed), sharpness of bit, type of bit (shape >and structure of point), single pass/double pass, type of block being >drilled, >whether bit is cooled frequently, etc., etc.............. > >Jim Bryant (FL) I agree that there are many variables and I think that the path to the most consistent results is to control or eliminate as many of those variables as possible. That's why I think the two pass method is superior to the one pass method. It eliminates some of these variables. Without an automated drill press I can't consistently control the vertical penetration speed. If I don't have some sort of cooling apparatus I can't control the drill bit temperature. I always use the same pinblock material and the same type of drill bit with the drill press always at the same speed. If I use a sharp bit then I can eliminate the drill bit, drill speed, and block material as variables (except to the extent that individual pinblocks will vary somewhat because they're made of a variable material - wood). Since I'm using two passes what I do on the first pass becomes less critical. How many plunges I use, the temperature of the bit, and the feed rate are essentially irrelevant because they're not affecting the final hole. The second pass is removing so little material that there's little obstruction for the bit. The bit doesn't really heat up so bit temperature is removed as a variable. I can't prove it, but my thought is that feed rate is not very important because so little material is being removed. So feed rate is essentially eliminated as a variable. This is not to say that my results won't differ (maybe markedly) from someone else's. They may be using a different block material, drill bit type, drilling speed, etc. But once I've established the block, drill bit, drill speed combo that gives me the result I want then I can more consistently achieve those same results with the two pass method than with the one pass method. One of the consequences of having so many variables affecting the process is that a spreadsheet like the one Ron posted may have limited usefulness for providing me with resultant (or absolute) torques, unless the person making the spreadsheet uses the same process that I do. However, it's still useful for comparing relative torques for different pinblock materials and sizes of bits and to give some indication of how much torque will change with time on a given type of pinblock material. Assuming that Mike used a consistent process then that spreadsheet shows the variation in torque for changing two variables, pinblock material and drill bit size. Perhaps someone else wants to take on the project of coming up with a spreadsheet of torques for change in the other variables of bit type, temperature, speed, sharpness, and feed rate (assuming that we don't take into account the variation in drill bits that are supposed to be the same size). I'm a little pressed for time at the moment. Phil F Phillip Ford Piano Service & Restoration 1777 Yosemite Ave - 130 San Francisco, CA 94124
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