%%%%%%%%%%%% HINTS & KINKS %%%%%%%%%%%%
1. Don't try to thread "hardware store" iron(steel) or aluminum by single point cutting on a lathe, at least to begin with. Those materials have practically no alloying agents, are "dead soft", tend to work harden, and are so gummy that they tear instead of cut. They do tend to bend well however and are useful for other purposes that "Harry Homeowner" might do on weekends. That being said, you may also get various pieces that may break instead of bend; there is no telling. These particular pieces that break instead of bend may tend to machine better than the pieces that bend well without breaking. I have gotten some "keystock" (the square cross section, zinc plated steel often sold in 12" lengths) that broke instead of bending when hammered over 90 degrees cold in a vise. It tended to machine rather decently. The "gummy stuff" can be machined, other than threading, using higher speeds, shallow cuts, sharp tools, and plenty of cutting oil but high speeds and shallow cuts are not what are available in single point lathe threading. The "gummy stuff" reminds me of "boiler plate" that used to be used to armor wooden ships so that it would deform and "catch" cannonballs instead of breaking like harder materials. It has its place but is not "screw machine stock" by any means.
2. Try assembling everything onto the lathe bed before actually mounting the split nut assembly to the carriage. This "dry fit" shows how verything goes in its operating position just to see how it all works. The pulley setups can even be done and the split nuts clamped around the leadscrew although they will not be attached to the carriage at this point. You can see that the Headstock-Bearing-Block is supposed to hang out over the end of the lathe bed. (A couple of people asked about this before they realized what was going on) This eliminates a long cantilevered overhang of the leadscrew shaft beyond its supporting bearing which would occur if the bearing block ended at the end of the lathe bed.
3. For the first time in tightening-up the Headstock and Tailstock Leadscrew-Bearing-Blocks, slide them into the center of the lathe bed to use a section of this shallow dovetail that will not be used in their later normal in-use position. Since the first installation may involve some extra force, any wear-and-tear to the lathe bed dovetails at this point will not be important in the positions that they are later used at. Sliding these dovetails around a little bit will also clean out the lathe bed ones and also allow them to form identical seat profiles a little better.
4. Dissassemble and reassemble the split-nut mechanism once to see how it goes together; it will need adjustment later anyway and this way you will see how it works. Remove the spring first using long nosed pliers and the nuts *in their open(relaxed) position*. I'll send you a new one right away in an envelope if it jumps and gets lost. It is made from .035" diameter Music-Wire bent around a 5/8" diameter mandrel if you want to make one yourself.
5. Drilling the #10-32TPI tap hole for the Pivot-Screw that holds the Split-Nut-Mecanism to the carriage can be done with a hand drill. The carriage material drills and taps very nicely so there is no worry about its machinibility, e.g., guminess or hardness. It is a little softer or less dense feeling than most wrought aluminum stock and is about 3/8" thick at the point where the hole is drilled and tapped. If you drill and tap the 10-32 mounting hole by hand I recommend using any aid you can come up with to help keep the drill positioned parallel with the ways with as little uncertainty and wobble as possible while the hole is being drilled. Since you cannot see the drill from two directions at once, having someone with a "good eye" or using a mirror to judge the alignment from the direction perpendicular to your direct line of sight would be helpful. Alternatively, this is where the electric hand drills with a bubble level on them might be useful if one has one. Maybe a piece of clay holding one of the small "line levels" will do here temporariy. The "line levels" are small spirit levels with hooks on both ends about 3" apart for hanging on the midpoint of a string to make it (very approximately) level. Then run the hand drill and just hold it in position to see how level you can hold it while it is running using whatever alignment aid you are using. There is no hurry here so take some time and practice. Try starting and stopping the drill while holding the drill level. It is surprising how a little side issue like clicking the switch on the drill will cause it to wobble when you have a way to tell what is happening. Practice until the trigger pull goes smoothly. Then, finally when drilling, run it in just a little and then pause with the drill still running to see how level and square you still are. Readjust and go a little furrther. The hole that results might not be as clean as one that is quickly drilled straight through but it is more likely to be square and level overall. Don't be an ostrich here and close your eyes and barge ahead. There is considerable depth to the hole so that plenty of holding power will certainly be obtained. Also these threads are not subject to constant wear and the load on the attachment, while moderate, is nothing close to what would be applied if the bolt were hex head and tightened with a wrench. Also remember to level the bed if using the bubble level approach. There is obviously no point in holding the drill level if the bed is not level. Use some oil on the drill guide and in the hole. Letting the handrill sort of "float" in ones hand while drilling may help with this. This is the same principle offered in holding a golf club and so many other skilful enterprises. Use enough force but not more. Not much force is required to drill this aluminum with a reasonably sharp drill although a drill with 135 degree split point or with the web thinned at the tip will lower the drilling force and be useful if this hole is hand drilled..
The tapping should be done with the same constant checking with the added advantage that you do not have a running drill in your hand when you pause. After the first four, five or six threads are cut then the tap will want to go in the direction it is pointed. Remember, a tap does not follow the drilled hole. If you want to redirect it at this point I would say back it out to all but about one or two threads or to where it feels loose and let it recut its way back in in your rechosen direction. Twisting it in its hole might work since a 10-32 tap is fairly robust in aluminum but my preference is to do it close to what I said.
If all fails there is still a way to correct the situation. The hole can be replugged with a short piece of 10-32 threaded aluminum stock ("allthread",that I will gladly send to you) and the whole process repeated. I did this several times while developing the prototype and have about three overlapping threaded plugs in the original carriage. I used epoxy to lock the threaded plugs in place and I believe that with the wedging effect of the threads in their tapped holes that to pull the final threaded bolt out would be just about as hard as to pull out the original one. So there is no need to get too nervous about drilling and tapping the carriage.
I might also say that to try to eliminate any sideways force on the drill guide while starting the drill would be helpful. In fact if one could put a coat or two of nail polish or quick drying paint on the pivot end of the leadscrew, this would tend to hold it centered in the tailstock bearing block a little better than having the pivot point itself do this chore. I have thought of painting the tailstock end of the leadscrews with some paint that the user would then remove after he drilled the 10-32 mounting hole but have not done this yet. Any type of tape I tried was too thick. Not quite sure of what kind of paint would he best. You may notice that the holes in the split nut levers are slightly elongated. One user reported that he had some trouble with the steel top slide of the lathe bed not being exactly parallel with the lower aluminum extrusion. The slightly elongated (by about 0.040") holes in the levers are to try and accomodate a little of this misalignment that may exist. I am informed by the people out in Arizona that there might possibly be a little horizontal misalignment of these two parts of the lathe bed although the vertical alignment should be good. One can appreciate this if one realizes how the two parts join.
Finally it might be mentioned that one idea was tried that did not work very well. One of the circularly symmetric bubble levels was mounted temporarily on the back of a hand drill to keep it oriented in the vertical direction with the lathe also mounted in the vertical direction similarly as it would be in a drill press setup. These are the types of levels that look like a bullseye and allow leveling in both horizontal directions with this single device. They are usually made of plastic and are less than 2" diameter. The difficulty was that the bubble bounced around so much as a result of the vibration when drilling that it was impossible to use it as a centering device. Perhaps two of the typical vial type levels mounted at right angles to each other would work here due to the greater degree of damping that these devices have but the circular type did not work.
6. When cutting left-hand threads give the fiberglass reinforced neoprene DOUBLE SIDED timing belt a shot of SILICONE SPRAY LUBRICANT. The neoprene belts from Gates Rubber Company are all made with a nylon coating on ONE side (the toothed surface) however the double sided belt is also coated on ONE SIDE ONLY (that is what I was told by the supplier who asked the manufacturer after my inquiry). I could not get a double sided polyurethane belt in our required length so had to stay with the neoprene. The silicone spray will allow the teeth of the neoprene belt to settle more easily into the pulley grooves to give proper indexed position without them having to force against the belt wanting to run in ordinary (frictional) flat belt mode of operation. A little of this lubricant on the plastic bearings and the polyurethane belts also does not hurt. This invisible treatment seems to last forever.
7. I recommend that the pulley changing routine be accomplished by removing the short arm of the Pulley-Carrier-Frame. This involves removing (or just loosening) the outer 1/4-20 Hex-Head Bolt and pulling the tongue-and-groove joint apart. This joint may be tight at first and will loosen eventually with use or can be loosened by CAREFULLY AND LIGHTLY narrowing the end of the 1/2" square cross connecting post with a fine toothed flat file(the tongue part of the joint) to free it up a little. Do just a touch of the file here first to see how it goes. A little looseness or tightness here should be of no concern. The graphite/nylon bearings in the two arms are intended to tolerate some misalignment. A little bit of an oil film on the tongue-and-groove joint will tend to keep the aluminum surfaces of the joint from galling each other and will extend the life of the 1/4-20 threads in the cross member. These threads were made particularly deep to allow a long bolt with plenty of thread engagement for longevity.
8. One will discover that tightening the Pulley-Carrier-Frame to the TAIG headstock with the hex head drawbolt tends to pull the belts up tighter than they were just before this tightening-up process was accomplished. This is because the Pulley-Carrier-Frame tends to be "rocked" slightly as the face of the frame is pulled flat against the headstock. Note that this is not the same large scale motion used in rotating the carrier frame to make belt adjustments but is instead more like the motion that would be caused by sliding a shim out-from-under the lower half of the longer pulley frame member where it contacts the headstock. For this reason the upper belt may get pulled excessively tight while the lower belt may be loosened slightly when finally "snugging down" down the Pulley-Carrier-Frame. A slight compensation for this effect before tightening is a reasonable solution to the problem. I tend to readjust it a time or two. This effect is present with both the Right-Hand and Left-Hand threading setups. Actually the Left-Hand threading setup is easier to readjust in this sense since the Idler-Pulley-Arm can simply be loosened and then retightened to eliminate some of the extra tension on the upper (double sided) belt in this case.
9. Before the snap-action-grooves are cut into the handwheel shaft for the Snap-Out-Handwheel modification, the handwheel may be used without these grooves but still using the eccentric bushing and spring clip supplied with kit. The clip is strong enough to keep the handwheel from falling out so that it can be pushed and pulled in and out of engagement with the gear rack. It simply will be lacking the snap-action. Also at first maybe only one of the two grooves needs to be cut. This groove would be the one that keeps the handwheel from being pulled completely out of the carriage since the stop to the push-in movement is already limited by the handwheel hitting the bushing even without a groove. The snap-action resulting from cutting only the "pull-out-limiting-groove" causes the handwheel to be pulled out very easily but pushed in against the camming action of the spring. In other words the handwheel will be held in its disengaged position by the groove but held in the engaged position only by friction.
10. A user reported that he had a problem because the steel dovetail part of the lathe bed was out-of-parallel with the extruded aluminum part of the dovetail. This would cause the leadscrew not to be parallel to the motion of the carriage and therefore a problem of binding even if the nut-plate adjstment was done properly. He solved the problem by putting a shim under one of the bearing blocks to get the leadscrew more parallel to the steel part of the lathebed. If you feel that the rotation of the leadscrew becomes tighter at one or both ends of the carriage, you might visually check the alignment of the leadscrew with this part of the bed. An innaccurate adjustment of the split-nut-plate would give a more constant drag on the rotation of the leadscrew because its angle would be constantly off regardless of the position of the carriage. It is not likely that such binding is due to innaccurate manufacturing of the two leadscrew bearing blocks because the hole in the tailstock-block is match drilled to the headstock-block while they are mounted next to each other by their dovetails in a jig during boring.
11. A calibrated dial (with 50 or 100 subdivisions) can be attached to the end of the leadscrew to give calibrated movement of the carriage in 0.001"or 0.0005" increments. This is obvious but also the same dial can be used on a longer 1/4" shaft that is installed in the N2N3 cluster gear position in conjunction with the Metric leadscrew. If the 22 tooth pulley is mounted in the N3 position and the 28 tooth pulley is mounted in the N4 position (on the leadscrew) than carriage will move in increments of 0.02mm or 0.01mm for each dial division. With the metric leadscrew the movement will be exact and with the original 20TPI leadscrew the movement will be short but within less than 1/4% . Do I need to mention you will need a "dummy" pulley also mounted on the extended shaft to keep it from being pulled out of position. Also the 1/4% means that the error will be less than 1/4 of one division if you turn the dial 100 divisions. For a few dozen divisions this error is almost unreadable. Of course you can compensate here too. If you like the "numbers" that make this work all you have to do is realize that the 22/28 ratio of the two pulleys modifies (slows down) the 14/11mm advance (per turn) of the metric leadscrew to a (22/28)*(14/11)mm = 1.0mm advance (per turn) of the calibrated dial.
12. That little Nylon post which guides the belt on the Left-Hand-Thread-Cutting-Attachment can be screwed in and out of the aluminum arm it is embedded in. It is screwed into the hole which is threaded. It should guide the double sided belt onto the tensioner pulley similarly as the flange of the N2 pulley does for the appropriate directions of belt travel.
13. If you are thinking about adding something like a slow speed motor for fine feed, an odd combination of large pulleys, or any other unimaginable modification to the TAIG/MM-Threader then maybe using some corrugated cardboard from old boxes to make preliminary parts will pay off. Even though these will not be exactly equivalent to their metal counterparts, they are alot better than a WAG (Wild Ammagined Guess) as to what the part ought to look like. No matter how good you (and I) are at building/designing things, we can almost always do things better the second time through than the first time. Doing things in cardboard with a pair of scissors(tin snips), a knife, and some glue the first time through is alot easier than cutting the preliminary parts from metal. Also making some pulley outlines from cardboard and wrapping a string around them should give a pretty good idea of what belt length might be involved.