A common problem facing woodturners is how to hold pieces in the lathe. The usual options, such as faceplates, scroll chucks and spur drive centres deal with almost everything perfectly well. But sooner or later there is something different needed. Often in these cases I use my homemade chuck. This is simply a holder, made of steel and mounted on the lathe spindle nose, into which a variety of special purpose inserts can be fitted.
I often have to turn items with a half inch diameter axial hole. In these cases it is usually best to drill the hole in the blank before the turning is done. If the hole is used as the location for turning, it remains true in the finished item. How to hold it in the lathe so the hole is central? Till now, for larger holes, I have either used a conical tail centre in the headstock to drive by friction, or a counterbore with a pin to locate in the hole. Both are liable to slip on larger pieces.
So I made a taper pin for the insert chuck. I cut a piece of mild steel rod about 2.5 inches long and 5/8 inch in diameter and used my old Atlas metal turning lathe to reduce the diameter to 1/2 inch over part of the length, to fit my insert chuck. Then I reversed it in the lathe and turned a gentle taper, leaving it just under 1/2 inch at the end, so it would slip about 1/4 inch into a 1/2 inch hole. Then I filed a flat on the shank where the locking screw bites, and the job was done. An insert like this could also be made from a soft steel morse taper with enough length to turn the taper on its nose, a job that could be done by hand in the wood lathe. For light work, it could be made from hardwood.
The taper has to be right, though I haven’t measured it. It’s not really critical, but too steep and it will not grip well enough, too gentle and it can split the wood. A little steeper than a morse taper but not as steep as a tailstock dead centre is about right. If the drive does slip, I can just tighten the tail centre a little more.
I used the chuck to make some wooden cylinders about 4 inches in diameter. Mounted on the taper, with the tail centre to keep them in place, they turned easily and accurately.