I build a lot of handles with wood and antler/bone mixes.I have always had trouble counter boring after turning the handles. I also bore them out and use foam arbors to lighten the handles. I have tried the pre boaring, gluing in the arbors mounting them to the mandrel and turning.too much slippage on the mandrel. Using the flexcoat pilot bit system where you build your own pilot bits. Get about two handles worth and have to rebuild due to the hardness of horn/antler. Found a place in Tennessee called Morris Tool that has Counterbore drills with a 5/16" or 3/8" pilot hole that you can use a piece of tool steel inserted into it for the pilot. I bought both the 5/8" and 13/16" with a 5/16" counter bore drill hole. These have 1/2" inch shaft, but if you hang out your tool steel about an inch you can use it in good Cordless drill with a 3/8" chuck. I used the cordless because iot turns slower than a regular drill. These are QUALITY BITS and made short work of the last batch of handles I made. I bored the 13/16" for the reel seat insert, hit it with the drum sander till the inset is right take the 5/8" bore out the rest and use 17 mm foam arbors and are done.
I am probably not describing it well. I will post a photo tomorrow but here is the link so you can kinda see what I am talking about.
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www.morriswoodtool.com]
