FINAL REPORT ON TEACHING A LATHE COURSE, IN THAMES NEW ZEALAND
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I am writing this report to help anyone else who may want to run a similar course for a community group like Men's Shed.?
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Well, we had our last course today. We had originally planned three separate workshop groups, each lasting 2 hours on 2 or 3 days. Surprisingly it worked out that we could cover sufficient material to do it in shorter time. We had 10 students,? The first 3 were our guinea pigs and we ran two classes of 2 hours. Then the next batch ended up being 7 students in a single class for 3 hours. We cancelled extra classes we had planned.
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Although, this is for the "Men's Shed" it has become very popular with women as well, and 6 of the 10 students were women.? None of the students had any lathe experience and only a couple had used a wood lathe, but they were all highly motivated and enthusiastic to learn. So this was a very satisfying experience for the two teachers. ?
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I am not a professional engineer, but my partner, Peter Woodford was a fitter and turner originally from Dorset and trained by the British Military. Twenty years of his career was in production engineering with the New Zealand company? Fisher and Paykel, making home appliances such as washing machines and dishwashers etc. He had to do quite a lot of work on the old donated Myford lathe to make it useable before we could run the course. We had two 3-jaw chucks with significant problems with runout. By switch back plates and jaws he was able to reduce runout to 0.007".? The Chinese Alloris style quick change tool post was rounded on its mounting surface and he had to mill off 0.3mm to make it flat! We only have 2 tool holders to fit standard cutting tools. We had to change tools in the tool holders and re-adjust the center height each time, but that added to the learning experience.? It all worked out perfectly in the end.?
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The room is small but Peter set up a 42" closed circuit TV with a camera mounted high up near the foot of the lathe and a light high over the head. This meant that students standing around could either watch directly, or watch the TV screen.
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With the second group being bigger we changed the structure of the course as follows. ?
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We started the class at the lathe pointing out the basic components, the importance of the axis through the spindle and tailstock and the parts of the saddle with movement along the bed being parallel to this axis, and the cross slide being perfectly at right angle to the axis. Demonstrated how the various knobs provide movements in these directions. Talked about backlash and how to compensate for it.? Then inserted a piece of stock in the 3-jaw chuck and turned the motor on at a good speed to point out what might happen if clothing or hair were caught in the chuck.
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I then used the 42" TV for a brief presentation of safety rules and gave them a handout of the list including the important ones like NEVER leaving the key in the chuck, and rules about using a file or emery paper.? Peter suggested avoiding emery cloth because it is so strong. Instead use strips of emery paper which tears easily and of course never wrapping stuff around your fingers.? It also included instruction for startup and shutdown including cleaning the machine and oiling all exposed metal surfaces. Another handout included a list of useful links to YouTube channels including my own, Quinn Dunkie's BlondiHacks and Joe Pie's.
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Then we went to the tea room where we could all sit down for more theoretical discussions. We had a huge spread of lathe parts, tools, and accessories, There was also a show-and-tell section of things we had made. A small bronze bell was a favourite, bronze balls, bronze coins weighing exactly one Troy ounce (31.1 grams compared with the cooking ounce of 28 grams), a dodecahedron, ball turner, jigs, Hero's steam engine with parts made from stainless steel, brass, or spun copper, and a model gold mining stamper battery were on display.?
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This section started by taking the jaws out of a large 3-jaw chuck so that they could see the internal mechanism with a scroll, and demonstrating how the jaws can be switched to hold larger objects using a pipe that could be held from the outside for boring, or held from the inside for external turning. We showed how the teeth on the back of the jaws are curved to fit the scroll. This is why two sets of jaws are required.?
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Then we had a four-jaw chuck holding a rectangular block and proceeded to show how they operate independently with separate screws with straight teeth on the back. This is why one set of jaws can be reversed.?
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We talked about various ways objects can be held:
Using a center in the tailstock to support long rods that are over 3 times their diameter.
Turning between centers with a dog.
Using a faceplate.
Even wood turning with wood screwed onto a faceplate to make a pattern for spinning copper.
Knurling tools and samples of what they produce.
Peter has a sample of a stainless steel shaft for a washing machine with a full depth spline made with a special knurling tool.
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One of Peter's samples had really pretty patterns on its surface caused by chattering setting up a harmonic vibration.
This was a segway into discussing the causes of chatter.
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We looked at a whole range of form tools for turning curved surfaces pointing out that the load on the tool is increased, causing chatter.
We showed the removable indexed carbide tips that we usually use on this lathe. Pointed out the chip breaker ridge behind the cutting edge.
Showed hand ground high speed steel cutting tools, and briefly reviewed the need for clearance and how the rake angle can be set to 0 degrees for brass, about 10 degrees for steel and 20-30 degrees for plastic, but otherwise you don't have to be too fussy about the angles for hobby work and can just learn by trial and error. These hand ground tools are generally used for special purposes when the carbide tips will not do the job. Some would argue with these suggestions but they make it easier for a beginner.
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At that point we split our group of 7 students into two groups. One group stayed with Peter who demonstrated an extensive range of measuring tools discussing their pros and cons. This took quite a while. Meanwhile, I took a group to the lathe for practical experience, and later the two groups switch places.
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I took a group to the lathe and demonstrated how to touch-off the surface, and then set a depth of cut and face it off. Then each student copied the technique and faced it off again. Then we repeated the process for turning (sliding parallel to the bed). Touch off, set the depth of cut and then make a cut. I used brass because it is easy to machine and is aesthetically pleasing to see the shining golden surface. I was able to buy 25mm diameter brass shaft about a meter long from a local second hand junk shop.?
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One of the students wanted to make some brass weights to hang on the ends of strings on Venetian blinds. This required two more operations. We were not cutting to any specific measurements, just demonstrating the method that could be used.
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We set the compound slide to 10 degrees and cut a taper, with each student cutting a bit more off the taper. Then we used a center drill, pointing out its rigidity and how it could be used with a live or read center in the tailstock. But in this case we were using it as a pilot drill, and then drilled a hole 25mm through the center.
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Finally, we parted it off, with each student taking turns during the parting process.?
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If we had time Peter also taught some students how to quickly set up a 4-jaw chuck using a dial gauge. After the class I went home and tried the method myself on my lathe and it worked perfectly. The secret is not to overthink it. Don't use the dial gauge until the very last stage when you can barely discern any runout by eye. Until you reach that stage you do it by eye, without being fussy about how much you move the work in each step. Do not over tighten the jaws at right angles. If you do the work will not move, and when it does move suddenly it can gat badly out of center. ?
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The students finally had several pieces that they had made and found it very satisfying and instructive. They seemed to leave full of confidence and enthusiasm. We asked whether it was too much material. They did not think so, but realized that they wouldn't necessarily remember all the details. But they had a good grasp of the general principles. They loved the show and tell, which illustrated the possibilities.
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So this seems to have been very successful and I hope it provides a template others might use in the future.
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Evan
Lathe: 1955 Boxford Model A with screw cutting gearbox, power feed with several accessories, hand tools and a pillar drill press.
Try my Free Online Gear train Software:
You enter a thread pitch or TPI and it shows you a range of gear trains and gearbox setting to use and even a scale drawing of the gear train.
It also includes calculations for taper turning by the tailstock offset method, and cutting speeds.
It includes the specifications for many thread types eg metric, UNC, BSW, and BA.
Displays drill sizes for tapping threads at any percent thread depth (with full explanations).
My YouTube Channel and Playlist about using an engineers lathe: ?
Project to build a Greek Hero steam engine and measure its power output:?
chrisser