Re: What is a "pot chuck" (step collet) used for and how do you use it?
I use them to hold the TEENIEST amount of precious material possible when turning it. By cutting a dovetail shape around the perimeter of the recess I turn in the chuck,I have been able to hold rare woods and other materials by just 1/32" of it well enough to cut threads in it,and hollow out pill boxes,etc. Hardly any material is wasted. Use a regular 3 jaw chuck,and you are going to waste an inch of it,or so.
I generally find these step collets partially used and they cost only a little,and last forever since I only occasionally need them.
Another good(18th.C.) type chuck is the pitch chuck. It is a round metal chuck with no moving parts. The chuck could be 6" in diameter,1 1/2" deep,and just hollowed out until there is 1/4" thickness of metal around the edges,and maybe 1/2" at the bottom. There would be a neck sticking out the back,threaded to fit the spindle on an old fashioned lathe.
This chuck is poured nearly full of hot pitch,like Burgundy pitch. A pitch of any kind that cools to a pretty HARD state will work. Asphaltum is too soft. You could add some powdered chalk to it to stiffen it up when it is cooled. The odd shaped part you want to hold,like the fancy base for a brass candle stick,is pressed into the heated pitch. The chuck is mounted on the lathe while the pitch is still soft enough to be pliant. The chuck is hand rotated while the item is nudged till it runs on center,so you can cut decorative rings into it,or thread it,etc. The lathe is kept slowly turning till the pitch gets hard(so the part can't start to sag),then,the work can begin. To get the part off,judiciously warm the pitch till the part can be popped off WITHOUT a bunch of TOO SOFT pitch adhering to it. Any pitch that does stick can be removed with a suitable petroleum based solvent easily.
If you make model engines with odd shaped parts that are nearly impossible to grasp for machining,this chuck would be very useful even today. Just be sure to take LIGHT cuts.
If you find this information useful,please write thank you on a $20.00 bill and mail it to me.
