No 19 TPI on my EE, Why?
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  1. #1
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    Default No 19 TPI on my EE, Why?

    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.

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    Apparently not commonly found on old American iron checked my lathes all went from 18tpi to 20tpi.

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    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.

    Sent from my Nokia 8 Sirocco using Tapatalk

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    So stick in a 95/100 compound and charge ahead

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    The Rivett 1020S has 19 tip.

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    I guess I'll just have to use my Chinese Enco backup lathe. It has 19TPI.

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    Daryl, I’ll make you a 95/100 Gear if you can wait a bit.

    John

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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.

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    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.

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    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

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    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.

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    Quote Originally Posted by Jimbojet View Post
    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.
    ..or some of those "realizable" may be of no initially obvious use.

    My I/M HBX-360's "Whitworth-Sellers-Briggs" (AKA "inch") selector also lacks the 19 TPI sought here..

    But it DOES have a setting for "19 1/5".

    Anyone know what THAT might be used for? Besides the metrifucated French mebbe simply takin' the piss 'coz the rest of the geartain happened to provide it (plus a few OTHER "fractionals") as a byproduct?

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    Quote Originally Posted by bll230 View Post
    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

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    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!

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    So what is the consensus of the best way to go about this, a 95/100 compound gear or a 57/60 as bll230 suggested?

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    Quote Originally Posted by daryl bane View Post
    So what is the consensus of the best way to go about this,
    Where taps and dies can't work? Or sometimes even where they might?

    Farm it out to he with CNC, else "no bid" it.

    Done the numbers on recovering the T&M costs?


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    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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