The Complete Online Guide to Knifemaking, PIN and BOLSTER HOLES
Drilling pin and bolster holes should always be done prior to heat treating the blade. For this reason, we recommend drilling pin and bolster holes immediately after the blade shape has been profiled. Drill holes that are one size larger for a slightly loose fit. For example, a size F .270 drill bit for 1⁄4 inch pins or a size #30 .1280 for 1/8 inch pins. These oversize drill bits may not be available at the local hardware store but can be found online at Granger or other machine shop supply sites. This way, you will not have to sand and polish the pin material or struggle to get them to fit. Try to chamfer each pinhole. It makes inserting the pins a little easier and also eliminates a bur on the blank that could prevent the blank from sitting flat during future machining. Our friend Steve Graham suggested painting the ends of the most commonly used drill bit sizes with colored nail polish. This simple trick makes finding common drill bits easy and can save a lot of search time.
At some point in time, mistakes will happen, and you may be faced with a pin hole that was not reamed out prior to heat treating. It's almost impossible to drill or even ream out a hole after the blade has been hardened. In this case, you really only have a couple options. You can anneal the blade to soften it and then ream or drill the holes, or you can grind the hole larger. Grinding is usually done with a small grinding wheel on a Dremel. Another, and perhaps the easier, solution would be to use a smaller diameter pin material and fill the remaining void with epoxy.
Some makers drill extra lightening holes through the handle of the knife blank. These holes can serve two functions. They lighten the handle resulting in better blade balance, and they add extra surface area for the epoxy glue to better secure scales in place.
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