Thread: Tyzack lathe
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Jim Wilkins[_2_] Jim Wilkins[_2_] is offline
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Default Tyzack lathe

"James Waldby" wrote in message
...
On Mon, 02 Mar 2020 12:26:59 -0800, Stephen Dixon wrote:

Hi, I've just been looking at the questions above and notice
someone may
have gear chart for screw cutting imperial & metric. Any chance you
could send it to me or point me in the right direction. Thanks Ste


As Jim Wilkins mentioned, you can make a spreadsheet. Or, look
online
for program CHANGE by Marvin Klotz, and adaptations of it by others,
eg
David Forsyth. It is worth looking those up so you can read
Marvin's
comments about driving and driven gears, putting gears on banjo,
etc.

Eg: "Sets of gears need only be placed with 'drivers' driving and
driven
gears being driven. The actual order is not important, just select
pairs so that they fit on the banjo. So long as the correct ones are
driving, the ratio will be correct. Always cross check by threading
(just a surface scratch is needed) some scrap and measuring the
pitch
if at all possible."

In pictures of Tyzack lathes, it looks like some models have four
change gears for setting the reduction ratio, so the program
mentioned
above is applicable. Below is a somewhat simpler program, written
in
Python 3. It accepts either an inch thread count or a metric thread
pitch (in micrometers), with numbers below 150 considered tpi and
150
or more as um. For example, the command ./gearset.py 1000
looks for gear sets to make a 1 mm pitch (1000 um) and after a few
milliseconds prints out:

Target is 25.4 tpi = 0.0394" = 1.0 mm
tpi: 25.422 = 0.9991 mm ABCD: 45 55 50 65
tpi: 25.455 = 0.9979 mm ABCD: 20 35 55 50
tpi: 25.333 = 1.0026 mm ABCD: 40 50 45 57
tpi: 25.319 = 1.0032 mm ABCD: 35 45 65 80


That's a better approach than mine for a lathe with loose change
gears. I bought an abused South Bend Heavy 10 with the 70-speed
gearbox whose pitch settings I found by Net research and trial.

At the time I was doing optics which requires a somewhat different set
of metric moduli than nuts and bolts. I copied the metric modulus
formula into each pitch's block of cells, linked to a fixed cell
($col$row) containing the X/127 ratio, then tried different values for
X until I saw the fine pitches I wanted. 120/127 worked out better
than SB's 100/127.

The best answer was sending the work to a shop with a Hardinge HLV-H
after I'd figured out a practical design with my lathe and mill. It
was the proof-of-concept demo for a laser comm link between
spacecraft. I'd been assigned to the project as the electronic tech
and wanted to prove I could handle more design aspects of the job.

jsw