If you are fortunate enough to own and use a Taig micro lathe, with its distinctly different lever operated drilling tail stock, you'll probably agree that it is unique and a very nice lathe accessory to use. The tail stock unit itself is typical of the general Taig design. It features "T" slots along several of its surfaces to allow the operator to attach indicators and other machining aids that might be useful during use. That alone makes it a great choice for model makers. Unlike many other tail stocks, this one travels and clamps along the dovetailed steel lathe bed and the lateral adjustment is also made along a dovetailed track. Perfect set up when complete accuracy is important! What this means is that the Tail stock center / ram axis is maintained parallel to the lathe bed and its axis, even when purposely displaced laterally to cut a long taper. Accurate, elegant, but most of all, simple! Taig Micro lathe components are known to be very robust and very well designed, with that typical "Industrial" look to them and unlike other tools, are designed with the model builder in mind. They are built in such a way that room for individual improvements and modifications is allowed without the user feeling that he is affecting the original tool's performance.
One of these improvements is the building of a micrometer adjustable screw to allow very accurate lateral positioning of the Tail stock. This is of course done when one wishes to turn a long gentle taper such as those used on Morse taper applications. The problem is that up to this time it was only possible to adjust the tail stock, sliding it by hand, taping it with a small brass hammer or other implement of gentle persuasion, using an indicator to read off the amount of set over directly off the side of the tail stock center. Once the machining operation has ended, you would need to return the center point back to its original, hopefully perfect parallel position in line with the lathe spindle axis. Normally, this requires the use of a typical test bar and a dial indicator in order to very accurately replace the center back to no more than a thou or less. If one fails to do so, anything turned between centers will end up with a taper running along the turned surfaces. My goal was to be able to bring the tail stock to whatever offset I required but once finished turning, be able to quickly and accurately bring it back to parallel by just turning a graduated dial. If I could nearly eliminate backlash on the dial's screw down to near zero, I could just set it back to whatever the original dial setting was when the Tail stock read perfectly parallel. Even if I get a couple ofthous backlash, I could simply reset it past the original parallel reading and return it to the proper setting thus eliminating any possible errors intruduced by residual backlash. No more test bars or indicators would be needed!
I got this particular idea after looking over one of Nick Carter's many self designed and built Taig micro lathe accessories. Nick is probably one of the most creative persons I've ever known and one that has the unique ability to examine and solve complicated problems in the most elegant and simplest ways. Being an independent Taig tool dealer as well as prolific user, probably has a lot to do with the unmatched success of Nick's designs. This time, he simply came up with a little rectangular aluminum plate through which passed a screw that would bear and push the upper tail stock housing to whatever lateral position you needed it to be. As I looked at that little device, I had to think, "Man, why didn't I think of this!". The plate is attached to the back side of the lower Tail stock body with two small 10-32 cap screws and 3/8" x 1/8" thick "T" nuts the same as those used all over the Taig lathe. Of course, the back of the tail stock body has a built in "T" slot already, sort of like it's telling you the user, to "feel free to experiment with me"! To use, you loosen the side clamp the locks the set over and turn the knob to push it to a lateral position beyond parallel. A simple and as always elegant idea. I wanted to build on that idea a bit further so I thought that if I just drilled and tapped the Tail stock body to a convenient thread pitch, like 1/4-20, I could then build a matching pitch screw and a graduated dial to no only set the tail stock over to very specific amounts, but also return it back to its original position by just turning the dial back to the original setting.
I began the project by first preparing the plate that would clamp against the tail stock and act as the bearing to capture the little lead screw. I basically was building a small screw operated slide since that exactly how the Taig tail stock is designed to operate. I rough cut a piece of ½" thick aluminum plate to a bit wider than the tail stock body and about 1/4" more in length than its height. I lightly flycut all the surfaces an deburred all the freshly milled edges. I measured the center line position for the " T " slot and scribed a horizontal line along the lower edge of the plate. I them located cross marks at 3/8" from each edge to locate two equally spaced cap screw locations. This dimension is not critical as long as they are about an inch apart. I set up the plate on two parallels on the mill and through drilled out the positions with a #11 bit. I also counter bored for cap screw heads to a 1/4" depth. I tested the fit against the "T " slots and with two square nuts, locked it so it was centered along tail stock body. I located the lead screw hole position, centered vertically and ½" from top edge and marked it. I removed the plate and set it up on the mill for the drilling and reaming that was to follow. The lead screw is somewhat interesting as it has two threaded ends and a double diameter shoulder along the mid point of it. It was made as follows. I chucked a piece of aluminum bronze although any hard brass would have sufficed. I used bronze because it is slippery, super tough and besides, I happen to have a lot of it on hand. It began as a piece about ½" diameter and 2" long. I chucked it, centered on my four jaw and after facing the end, turned the first inch to .250". Then I turned the next 1/8" to .375". Using a tail stock held die, I threaded the end to 1/4-20 leaving a 1/4"long section of .250" diameter portion unthreaded. Now I flipped the piece end for end and gripped it carefully by the unthreaded section and began to work on the remaining end. This bronze is so darned tough, I could get away with gripping it without any protection. I then reduced the remaining ½" diameter to .250" leaving a 1/8" wide section of the .375" diameter portion intact. I chamfered all edges to remove burrs. Just as before, I threaded this end as well to 1/4-20 and reduced the total threaded portion to about 1" in length including the 1/8" wide .375" diameter shoulder. I ended up with a double sided 1/4-20 screw, one side threaded flush against a 1/8" wide .375" shoulder followed by a 1/4" long .250" diameter unthreaded section ( this makes up the double diameter section ), followed by the remainder, which is also threaded 1/4-20. Now I turned my attention to the plate which I had set up on mill, to machine the matching two diameter female recess and hole that will house the screw body. I located, center drilled, through drilled and reamed to .250". I followed with a bit about .008" to .010" under.375 and drilled to a depth of 3/16". I them reamed the shallow counter bore with a .375" reamer. The screw fit into the double reamed bore and rotated freely without any wobble. Only the threaded portion protruded out the back face of the plate where a threaded graduated dial would be installed so its face just touched the main plate. A drop of CA glue would lock the two together along the threads and allow the knob to spin freely with the .375" diameter section of the screw bearing against the corresponding diameter blind bore on the plate so there is no lateral shifting. The .250 portion spins inside the remaining matching part of the reamed plate bore. Before we get to far ahead of ourselves, we need to install the screw and the plate in position and drill and tap the hole into which the screw will operate inside the tail stock body. Attach the plate to the tail stock and center it as before. Using a 1/4" diameter transfer punch through the .250" hole on the plate, tap in the location for the threaded hole for the tail stock. Disassemble the tail stock and mount the sliding upper portion on the mill and drill it out with a #7 bit to about 1" depth and tap it to 1/4-20. Install the plate yet again to the lower portion of the tail stock and center it. Slip the screw into the plate screw bearing hole and push it into the double bore. A bit of white lithium grease helps here. Slip the upper portion of tail stock onto the lower dove tail and slide it until the tip of the screw begins to engage the threaded hole of upper body. Begin to draw the upper body inward by turning screw clockwise and continue feeding it until it has pulled the upper body as far along the dovetail as it will go. Chances are the upper body will be flush against the screw plate. Lock the side tail stock clamp of the dovetail securely. I filed a small witness mark on the top edge of the plate to aid in locating dial positions later.
Now for the dial that will work the screw. I took a slug of aluminum about 1" diameter and 3/4" long and after facing cuts, turned one end to about 5/8"diameter and ½" length, leaving 1/4" worth at 1" basic diameter. Basically creating a "T" shaped knob. I through drilled, tapped to 1/4-20 and counter bored the 5/8" diameter end to a depth of about 1/8" with a 1/4" bit. Using my side mounted, pointed engraving tool bit and my shopmade indexing plate on my Taig lathe, I proceeded to engrave 50 equally spaced lines along the edge of 5/8" diameter end to a length of 1/4". I faced the side that will bear against the plate creating a thrust bearing ring about 1/32 thick and ½" in diameter. This will be the only portion of the dial that would bear or rub against the plate. With some lithium grease to lubricate it, friction wear will be kept to a bare minimum. Now I just screwed the dial onto the protruding, threaded portion of screw until the thrust ring was in light contact with the plate. I then applied a small drop of CA glue to the threads through the rear end of hole on the fat end of dial and allowed the glue fill the thread gap and fully cure. I ended up with .002" total backlash which tells me my threads are pretty snug.
Adjusting the tail stock is now a cinch. Loosening the side clamp and simply turning the knob in the direction you want to displace the tail stock is all that is needed. You get a direct reading of the actual displacement in thousands of an inch. Clockwise rotation pulls the tail stock back toward the rear of bed or away from the operator. Turning the knob counterclockwise, pushes the tail stock to the front or towards the operator. It actually took a lot longer to explain and put this on paper than to build it, mainly due to my inherent long winded manner of explaining things. So don't despair and please consider to give this little project and bring your Taig drilling tail stock to the pinnacle of accuracy and performance with minimal effort and expense!
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