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No 19 TPI on my EE, Why?

daryl bane

Titanium
Joined
Mar 12, 2002
Location
East Texas
I was doing a bunch of British BSC, BSF and BSP stuff, and was astounded that my EE had no provision for 19 TPI on the gearbox. Seems 1/4-19 BSP is a relatively common thread around the world.
 
The first version of my lathe, an EE clone by CVA (later Kearney trecker UK) didn't have 19 but the later machines do, changed sometime pre 1964.

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After I sent John a PM on his offer, and said I just had a couple of these to do, I got curious on the math involved. So if I did change out the compound gear to 95/100, how does this work ? What combination of the settings would get a 19 TPI? Sorry I am just a bit slow in the brain dept.
 
The 95/100 gear ratio is the same as a 19/20 ratio (divide both numbers by 5 to see this). So the 95/100 gearing lets you convert the 20TPI setting on the machine to actually cut 19TPI.

Other thread settings that can work abound mathematically but perhaps not physically. For instance, to cut 19TPI using the 23TPI setting you would want gears with a 19/23 tooth ratio, or 38/46 (double the tooth count), or 57/69 (triple the tooth count), or 76/92, or ... you get the picture.

Any thread selection on the machine can be mathematically converted with the right gears to cut 19TPI, but those gears may not be physically realizable.
 
I said 95/100 as a quick answer, but the practical way to do it is make the 60 tooth idler a compound 57/60 tooth and then flip it over so the 24 tooth stud mates with the 60 and the 57 drives the downstream gears. 57/60 = .95

John
 
Upon further thinking since the gearbox has a 12 thread setting, simply replacing the 24 tooth stud with a 38 tooth stud would work. Much easier than making a 57.
 
Upon further thinking since the gearbox has a 12 thread setting, simply replacing the 24 tooth stud with a 38 tooth stud would work. Much easier than making a 57.

Maybe not - 12 TPI is .08333" lead. Multiplying that by 38/24 just makes it a larger lead

19 TPI is but .05263" lead
 
Dawggone it John, you are right. I am so used to working with gears I forgot to hit reciprocal on my calculator. In my pilot business it is called expectation bias. I produced the answer I wanted to get. Italian wine is my second hobby - I shouldn't post math responses after dinner!
 
Parts were done successfully on my dreaded "thou shalt not be named here lathe". But I have rec'd VERY kind offers to make a proper gear to do this on my EE. So what I am asking is, if we are going to make a gear what is the best spec, teeth, etc. to make a correct gear?
 








 
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