Seneca Falls gear chart

A

AHolst

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I have attached a picture of the thread chart on my Seneca Fall lathe (circa 1903). Also attached is a computer created file in PDF format of the data so it is more readable.

I have all (11) gears that are needed, but I am struggling to understand the chart. I have been successful setting up the gears to cut a 12 TPI thread. This works great. I thought excellent I'm on the way!!

12 TPI is setup using a 48 tooth gear on the stud and 32 tooth gear on the screw. The compound on the banjo gets both a 60 and a 40 tooth gear.

I tried setting up for 13 TPI with a 48 on the stud and a 52 on the screw as the chart show. Gears don't even get close to meshing. I tried adding the 60/40 on the banjo. Does not work either.

I can't figure out why the chart has so many spaces for the compound that are blank.

I will be eternally grateful if someone can straighten me out.

Thanks
 

Attachments

  • Lathe gear chart.pdf
    69.6 KB · Views: 14
  • Lathe thread chart.JPG
    Lathe thread chart.JPG
    497 KB · Views: 17
I would assume that the blank spaces indicate that no compounding is used, only an idler so that the gears on stud and screw meet up in mesh
 
It would seem that it matters what size idler is used. Correct?
 
AHolst said:
It would seem that it matters what size idler is used. Correct?
Click to expand...
Not at all, the idler needs to be big enough to connect the other gears, but due to the fact that the banjo swivels, you set the idler to mesh with the screw gear, then pivot the banjo to achieve mesh with the stud gear.
 
John is correct, you pick one of your other gears as a go-between to connect the 48 and the 52. Idlers have no effect on the ratio
-Mark
 
John and Mark

I set up the lathe as you suggested. You are absolutely correct. It worked exactly as the chart indicated for several threads that I tried. Thank you so much for helping this novice wanna be maybe someday hobby machine operator.

This has stumped me for several weeks.

Thanks again!!!!!
 
Another overlooked advantage to having change gears, you can cut 27 TPI, most QCGB cannot.
 
Yeah, I noticed 27 TPI on the chart. Not sure I have ever seen 27 TPI though. Where is it used?

Thanks
 
You'll find 27 on some indoor sink faucet spouts and also it's a standard microphone stand thread
 
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