MAKING A TAIL STOCK DIE HOLDER
Most small 4' swing hobby or model maker's lathes do not come equipped with power longitudinal advance or thread cutting capabilities, unless you go with the high end machines, so we must instead rely on taps and dies for all of our threading needs. After drilling a hole to a given tap size in a work piece with the tail stock chuck, you then replace the drill bit with the corresponding tap. The tapping takes place by loosening the drilling slide ( Taig ) or the tail stock so it can move freely and the stock is threaded by turning the head stock chuck by hand if the hole is small or with a lever for bigger, tougher tapping jobs. As the threading progresses, the tap and chuck will be drawn into the hole in perfect alignment because it is being guided in the same position by the drilling slide and or tail stock. That would take care of the hole itself. But what about the mating part that screws into the hole? It could, as in many cases be just a hole for a screw, or it may be for an actual component that must have a machined stud threaded to fit. Immediately after the stud is turned to the correct diameter, it should be made ready for threading with a die. A die will thread the out side of a turned stud or a plain piece of rod. In most cases the part is held in a vice and the die, whether round or hexagonal in shape, is held in a die wrench by a screw. If it's not held perfectly flat, it will in short order produce a lob sided thread. Following the tail stock tapping example, we can adapt a procedure to insure that the dies are held perfectly flat and in a straight relationship to the work, prior and during the complete threading procedure.
The following instructions will refer to the TAIG lathe but it could, with minor modifications be made for other makes. I mostly use 1" diameter round dies so my die holder is made to hold these as a slip fit. We begin with a 1-1/2" long section of 1-1/2" diameter aluminum or if available, free machining steel such as 12L14 grade. After facing both ends until free of any saw marks you can begin to drill a through hole to a final bored or reamed diameter of 1/2". Bore out one end to a depth of 1/2" to a diameter a few thousand larger than the round dies you will be using. As you near the correct diameter, you should begin to check the fit with the actual die until the perfect easy slip fit is achieved. Four radial holes are drilled around the perimeter of the die holding bore to take 10-32 set screws. A second set of six radially located holes are drilled approximately mid way along the length of the holder to a depth of 3/8" and 3/16 diameter to allow a 3/16" diameter turning lever to be used during the threading procedure. A 3" length of 1/2" drill rod is faced on both ends and one end is drilled and threaded to 3/8 - 24 to a depth of 3/4". This rod will screw to the Taig tail stock center and the die holder is slipped into it. The piece to be threaded is held by the head stock chuck and the die / holder sliding on the 1/2" guide, keeps the die centered and in line with the work. It is fed into the work with a 3/16 lever using the six holes around its perimeter. Just as in tapping, the die should be backed off after each half revolution to break and clear the chips. Lubrication formulated for the metal being worked should be liberally applied during the threading process.