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28th Jun 2018, 04:53 PM #1New Member
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Model C Gearing for Metric Screwcutting
I am a self-taught novice on my late father's Model C. I am looking to turn a 1.25mm pitch thread for a carburetor jet in a veteran car. Two questions:
1. the chart on the lathe gear cover specifies a 27 stud gear but the Hercus book (p61 of the 1980 ed) specifies a stud gear of 24. Which is correct? To confuse matters further the book specifies a gear number for 1.0mm pitch which has been crossed out and 27 has been handwritten there (by my father I assume).
2. a 63/60 compound gear is specified - does the 63 run closest to the lathe or the 60? I'm finding it a bit hard to work out the diagrams!
Jeff
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28th Jun 2018, 05:59 PM #2Most Valued Member
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Is the lathe a 9" or 260?
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29th Jun 2018, 12:49 PM #3Intermediate Member
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- Apr 2016
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Hercus_TextBook_of_Turning-31.jpg
Viewers should be able to download that image (after logging in) and then zoom in on it for the details.
This is probably a different (earlier) edition of the Hercus Textbook of Turning, with instructions suitable for 9" Model B & C, and it relies on using the 127/100 transposing gear.
In FIG 3., on the screw pitch thread chart on the right, (of Figure 139, i.e. "FIG. 3 on Figure 139", getting a little complicated) the marking of the 18T side of the 72/18 compound gear is omitted (design error, or perhaps they did not copy the South Bend chart they are cloning this from fully/correctly). Although there is present the unidentified arrow pointing at the (obscured) 18T gear (obscured behind the 72).
It appears to me that on this set of diagrams the 127 tooth gear of the transposing pair 127/100 is mounted closest to the headstock. (But I am not sure whether my interpretation of the diagram is correct, nor am I sure if the diagram is correct.)
For 1.25 mm threads, according to the chart, and diagram - FIG 2. in particular - the 127T side of the transposing gear drives the 40T stud gear and the 80T screw gear drives the 100T side of the transposing gear.
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29th Jun 2018, 08:39 PM #4Golden Member
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- Nov 2010
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- Gippsland Victoria
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metric threads
There are various books and web sites that explain how to do the relevant calculation that gives the you the final TPI for any given gear train. If you google "metric thread imperial lathe 8tpi leadscrew calculator" you will find various discussions and calculators
Here is a page I found useful Metric Threading
Best thing I found was a free program written by a chap on this forum called Vernon, the program was called lathegears and you give it a list of all of your gears and then the tpi of your leadscrew and it it will calculate what gear trains will cut the the required thread - you can set a tolerance on the required thread ie +/- x.x% -its a very very good calculator. Link below ...
Lathe thread cutting change gear calculator [Archive] - Woodwork Forums
Bill
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29th Jun 2018, 09:44 PM #5Most Valued Member
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Bill, unfortunately the link comes up with an "Invalid Attachment specified. If you followed a valid link, please notify the administrator"
KrynTo grow old is mandatory, growing up is optional.
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29th Jun 2018, 09:54 PM #6Intermediate Member
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- New South Wales
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29th Jun 2018, 11:47 PM #7Most Valued Member
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Just tried it again, it comes up with this page; Lathe thread cutting change gear calculator
Lathe thread cutting change gear calculator
I then click on "Here is the link http://www.woodworkforums.com/attach...1&d=1275121329"
Woodwork Forums
and I get "Invalid Attachment specified. If you followed a valid link, please notify the administrator"
So what am I doing wrong??
Thanks
KrynTo grow old is mandatory, growing up is optional.
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29th Jun 2018, 11:47 PM #8Golden Member
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Kryn,
More than one way to skin this cat ......Try this
Google "lathe thread cutting change gear calculator metalworkforums.com"
should be the first thing that google finds.
Problems might be due to archived tapatalk part of forums ... ? I dont know.
Bill
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29th Jun 2018, 11:59 PM #9Most Valued Member
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Thanks Bill, I still get the same message??
To grow old is mandatory, growing up is optional.
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30th Jun 2018, 12:20 AM #10Golden Member
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30th Jun 2018, 02:02 AM #11Intermediate Member
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- Apr 2016
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- New South Wales
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- 45
Whoops, now I am infected.
Lathe thread cutting change gears.jpg
Or more correctly I was infected all along ? The bird landing on its head corresponds to the file not being at the given location. "To be or not to be ?"
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30th Jun 2018, 09:40 PM #12Golden Member
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- Nov 2010
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- Gippsland Victoria
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Try this
OK original download links seem broken.
See attached zip file and output example called output.pdf
I don't think I am breaking any copyrights by putting this up - see attached jpg file called about.jpg where permission is given to distribute the program.
I've tried this zip file on a laptop and it works - don't extract the files into the official windows programs folder because if you do that you wont get permission to input your own change wheels.
Its a terrific program and the chap deserves lotsa applause for writing it.
Bill
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30th Jun 2018, 10:22 PM #13Most Valued Member
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- May 2011
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- Murray Bridge S Aust.
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Thanks Bill, Managed to down load it.
KrynTo grow old is mandatory, growing up is optional.
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