The Horia Micrometric Jewelling Tool # BG5372-61-4 is a very fine instrument that can, as its name suggests, adjust jewel position in extremely small and precise amounts. It has served me well for adjusting wheel and arbor endshakes, but for some processes it falls short. This tool has a 4mm hole in the stake as well as the soleplate, which allows me to use Seitz 4mm stumps and pushers. The stumps and anvils have 4mm posts and larger shoulders that rest on the soleplate. There are a limited number of different-shaped stumps for certain processes. However, the range of Seitz pushers is quite extensive. Many times over the years, situations would arise that I would have liked to use this tool, but the correct stump was not available.
I thought if I could use the pushers as stumps, I would have any situation covered. The trouble was that the 4mm pushers do not have shoulders and would drop completely through the soleplate. I needed to raise a pallet fork on its arbor and I wanted to use the Horia tool. Consequently, I needed a stump with a small hole to clear the arbor and a small, flat diameter to support the under side of the pallet. The correct size flat pusher was at hand, but I could not use it. This situation drove me to finally resolve the inconvenience.
The hole drilled in the under side of the soleplate is larger than the 4mm hole in the topside. I reasoned that I could create an adjustable stop in the soleplate. The bottom plate hole allowed a 5 x 1 metric (5mm diameter x 1mm thread pitch) tap to slip easily into it. Without actually measuring, this demonstrated to me that the hole was 5mm or very slightly larger. I tried a 6 x 1 metric taper tap, and it started to cut threads as shown in Figure 1. To compute the metric tap drill size for a metric tap you would use the formula TD=MD-PITCH, where TD is the tap drill size, MD is the major diameter of the tap, and PITCH is the millimeters per thread. This would cut an approximate 75% thread depth. Considering in this case that the tap was 6mm and the pitch was 1mm (threads are 1mm apart), the formula was TD= 6-1 or 5mm. Most likely a 5mm drill was used to create the bottom soleplate hole. Cutting fluid was liberally applied around the hole, and the body of the tool was held loosely in the tape-covered jaws of a bench vise. The body of this tool is cast and easily threaded by turning the tap one-third to one-half a turn to cut a thread, and then back one-quarter to one-half turn to break up the chips and allow them to escape out through the tap’s flutes. I tapped threads as deep as I could as shown in Figure 2. A bottoming tap was then used to cut threads as close to the 4mm hole bottom shoulder as possible as shown in Figure 3.
A rod that measured just over 6mm in diameter was chosen, mounted in a three-jaw chuck in the mini 7″ x 10″ lathe, and turned down to 6mm as shown in Figure 4. The cutting tool was then presented to the rod on an approximate angle of 10° as shown in Figure 5.
As mentioned previously, the pusher diameters measure 4mm, Figure 7. In order to variably adjust the height of a pusher, a post slightly less than 4mm was turned on the end of the threads. Figure 8 shows the thread and post nearly parted from the rod, and Figure 9 shows the relative size of this accessory.
The post end of the accessory was held in a watchmaker’s lathe that had been mounted on the x-y axis bed of a Sherline Mill as shown in Figure 10. The lathe head was locked to prevent rotation. Three thin slitting saws were stacked and held in a mandrel that was mounted in the mill head. The saw was then brought to center as shown in Figure 11. The threads were flooded with cutting fluid, and the saw was spun while the watchmaker’s lathe and head were moved very slowly along the x-axis (right to left) into the spinning saw as shown in Figure 12. The lathe was periodically moved along the y-axis (front to back) allowing the saw to cut a flat root in the slot. The finished, adjustable pusher stop accessory is shown in Figure 13. The pusher stop’s screw head is shown in the soleplate viewed from the underside in Figure 14.
I am now able to use any of the Seitz pushers as stumps. The pallet fork and guard pin shown in Figure 15 needed to be slightly raised on its arbor. With the adjustable pusher stop in place, I am able to use a pusher as a “stump” as shown in Figure 16. The correct sized “stump” stabilized the pallet as its arbor was pushed down a few hundredths of a millimeter at a time, as shown in Figure 17, effectively raising the fork and guard pin into alignment.
By Dale LaDue, CMW21