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:?
