Gingery (Gingerey?) describes wrapping a brass guide wire around a brass tube pressed over the work to be threaded, adjusting the wire pitch to match the thread to be originated in the work, soldering the wire to secure it, and using the wire to guide an adjacent cutter to originate the thread, which is self-guiding once originated.
Could this be done by modifying a thread insert of the correct pitch, "screwing" it over the work, adjusting the pitch, and using the thread insert (Helicoil) to guide the cutter?
It seems like this would save loads of time if you want to cut a thread that isn't on your lathe, or don't even have a thread cutting lathe.
I am looking at this method to originate threads directly on motor shafts. A small universal or PM motor, and the little three jaw chucks they sell at HF.
Yours,
Doug Goncz Replikon Research Falls Church, VA 22044-0394
How do you use a brass wire to guide a cutter? And in what sense is a thread "self-guiding once originated"? What kind of cutter would you use in what kind of setup? A lot of what Dave Gingery said made sense to me but maybe something is lost in translation, because this one does NOT.
That machine tool made from two engine blocks, some plate, a big spindle, etc, that was here, and has a yahoo group of its own, has a link to Gingery's method. ICRS especially the name of the machine tool.
A very light cut is taken first with a thread chasing tool. A bit of wood adjacent the tool accepts the impression of the wires, forming a sort of rack engaging the brass wire pinion.
Gingery says with the thread chasing tool, the thread, once well started, will guide the tool, allowing the thread to be deepened without changing its pitch. I've never threaded this way, I have used taps and dies and single pointed threads, but never used a chasing tool.
The kind of cutter would be a chasing tool with multiple, properly pitched, cutting points.
The original Unimat used a similar system to cut threads. A threaded spacer was mounted between the spindle and the chuck. Withe the spindle turning, a follower was pushed against the threaded spacer. This pushed the single point tool along the bed in unison with the thread on the spacer. With care,very fine threads could be cut. There were a number of threaded spacers available in various pitches
This would be like that, only part of the work would be used to guide the thread cutting tool.
How does the multi-point threading tool (chasing tool) work, anyway? I've never used one. Do you use it with a jeweler's rest? Does the work pull the tool along? Is it mounted in a toolpost? Does the carriage carry it along?
From what I have read, first the user had to develop the skill to move it at the right speed for the current spindle speed. Use a layout dye to make the scratches clear, and first make passes without touching to develop the speed, then lightly engage it, and move it sideways at the speed necessary so when a complete turn is made, the next tooth will be in the groove started by the previous tooth. If your speed is right, it will be visually obvious. If not, re-die coat and try again. Once the first good cut is made, you can visually sync your motion to the spindle speed to deepen the initial scratch marks until you get deep enough for it to help you.
As you get deeper, you get more assistance from the already cut thread in moving the chaser along, and the presence of multiple teeth in parallel helps to keep it at the right spacing, once properly started.
No to both. The *operator* provides the initial lateral movement, until the threads are deep enough so the chaser becomes self-feeding.
Note -- I have never done this. I've just examined the tools, and the old books, and read descriptions of others doing the work -- from long before the lathes had gear-driven leadscrews to make precise threads.
What I *have* done is to use the threading attachment which someone else described for the early Unimat lathes. The spindle on that was in a quill cartridge which could be extended enough so the master thread would form a cup around the quill. The master thread was mounted between the chuck and the chuck's backplate, using slightly longer screws.
For each master thread (steel), there was a brass follower which contained a segment of an internal thread to match the master thread.
The tool holder slid along on top of the t-slot in the carriage for a reference surface.
You held the follower engaged with the master, and the sliding ball firmly onto the carriage top.
The follower drew the whole assembly along in sliding bearings on the single rod to which it all was mounted.
When you released the pressure at the end of the cut, and allowed the follower to rise out of the threads on the master, a spring around the long rod snapped everything back to the start point.
And there was a small handwheel to advance the single-point threading tool.
There was sufficient give in the whole system so you could make several passes still removing metal from the workpiece before you had to re-adjust the depth of cut handwheel for another pass.
The whole thing could feed no more than about 25m (1") for maximum thread length.
But you *could* cut threads with it. I made some lens mounts using that system. By releasing the pressure at the right time, you could cut quite close to a shoulder with no real danger of a "crash".
I'd like to return to the OP. It seems like a Helicoil would work fairly well to originate a thread. I'm sure the Helicoil would still have the right pitch if wound onto some work.
Turning to my favorite topic, self-reproduction of machine tools, what kind of lathe configurations make for self-reproduction of existing threaded work, using the work as a pattern to drive the threading tool on the companion lathe?
I am thinking of a law of opposites or parity. If parity were assumed, any machine tool ever made would be made also in its reflected configuration. Without going into symmetry theory, we'd just envision a lathe for a left-hander, with the headstock on the right, the carriage in front of you, and the tailstock to the left.
It seems like having such a machine tool might allow self-reproduction of, say, a lathe spindle, by positioning the LH lathe behind the RH lathe, putting the spindle in the LH lathe, and engaging a bridge between the two. I wonder how simple a lathe could be and still cut something this way.
I wonder if a simple design rule would allow all instances of a self-reproducing universal machine tool to be configurable as their symmetric forms easily. I already have as design rules "You need two of everything" and "You need woodworking type of capability and metalworking capability in the same machine".
Something like Einstein's famous "Make everything as simple as it can be, but no simpler." Maybe "make everything as symmetrical as it can be, but no more symmetrical."
Thanks -- but perhaps the reason is that my body still remembers using one quite a few times. And I studied it with the thought of making more master threads and followers on other lathes (ones with screw-cutting gearboxes and leadscrews).
However, after experience with those better lathes, the focus turned onto acquiring one of them for my own use, because the Unimat had too many limitations.
Though I did have the power feed accessory set up to accept drive from a DC PM gearhead motor, so I could get a respectable range of feed rated -- even when I was in milling machine mode. (Since the original design took power from an extension nut/pulley on the spindle just outboard of the standard pulley which took drive from the lathe's own spindle motor.)
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