[How do I?] Do 20 TPI

I would almost suggest taking some spare stock and doing some test of all the diff threads in the 4 column as you say you have done most of the TPI in the C row.
Then see what it does, Then also try the 5 Column as well to see if gears are in wrong place or something.
 
By end train, I mean the gear train between the spindle and quick change box; by simple or compound gearing I mean that simple gearing is the two 40 tooth gears with an idler between them, and compound gearing is two sets of gears; such as the spindle gear driving another gear which is connected side by side with another gear, which then drives the gear on the QC box. When you cut metric leads, it is set up that way, when cutting inch threads the QC box gear is shifted over so that the transposing gears are only used as an idler.

Sorry, I just did not know the proper terminology, and I never paid attention to the set up since the 16, 18, 24, and 28 threads I cut previously came out right on, thus the reason I took for granted that 20 being on the same C gear, that it would be just fine. I have not threaded any metric.
 
I would almost suggest taking some spare stock and doing some test of all the diff threads in the 4 column as you say you have done most of the TPI in the C row.
Then see what it does, Then also try the 5 Column as well to see if gears are in wrong place or something.

That's a thought.
 
I agree that row B columns 3,4&5 have errors. They should be 9.5,10,11 These are errors on the label.
But that does not explain why other threads in row C thread correct and 20 tpi is wrong. Only explanation for that is a really hosed up label or the number of gear teeth for that spot on the gearbox is wrong.
What tpi does the machine cut when you dial in 20 tpi?
Next thing to try would be to cut something else from column 4 like 5 tpi. My guess is all the threads in column 4 do not match the label.
 
You've got something wild going on in that QCGB. I'm used to seeing the tpi doubling as you move down a row. For example, 4, 8, 16, 32, 64 down column 1. 4 1/2, 9, 18, 36, 72 down column 2. The you throw columns 3, 4, and 5 at us with 4 3/4 to 10? I'd have guess column three would be 4 3/4, 9 1/2, 19, 38, 76. Column 4 would be 5, 10, 20, 40, 80. Column 5 would be 5 1/2, 11, 22, 44, 88.

Can you try either the labeled 11 or 40 tpi in you column 4 and see what you get? Maybe a mixed up gear in the QCGB? That'd be tough to do as the pin hole and gear diameters are matched.

Good luck!

Bruce

Your comment, I think hits the nail on the head, the numbers on the chart do not make sense at all, they all should be (consistently) multiples of the upper rows of numbers.

Thank you.

I will try as suggested and report back.

Just for comparison, here is the label on my 1024.

20170925_170850.jpg
 
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I agree that row B columns 3,4&5 have errors. They should be 9.5,10,11 These are errors on the label.
But that does not explain why other threads in row C thread correct and 20 tpi is wrong. Only explanation for that is a really hosed up label or the number of gear teeth for that spot on the gearbox is wrong.
What tpi does the machine cut when you dial in 20 tpi?
Next thing to try would be to cut something else from column 4 like 5 tpi. My guess is all the threads in column 4 do not match the label.

The thread is 22 TPI. So I moved the R lever to 5 and made a readable scratch pass, hoping 4 and 5 night have been swapped, no joy, the scratch pass is not 20. Will get back to it later on.

20170925_172740.jpg 20170925_172907.jpg
 
So Column 4 row C cuts 22 tpi
Looks like Colum 5 row C cuts 24 tpi. (looking at your picture on the right).
In your first post you said you had successfully cut 16, 18,24 and 28.
That means you have cut Column 6 Row C and got 24 tpi.
That seems to say that your gear box cuts the same threads in Colum 5 and Column 6 And Column 4 is cutting what is labeled for column 5.)

My guess is they hosed up the assembly of your gearbox by leaving out column 4 gears and doubling up on column 6 gears.
Take a couple scratch tests with other rows and columns and see if this is consistent.

This is the kind of thing that earns a company a certain type of reputation.
 
the 20tpi thing is strange Bamban.
on my shenwai 1236, my threading chart appears to coincide with real tpi's, as does the baby jet.
i have not tried to thread over 36 tpi, but apparently we have capabilities to thread 112tpi
there may have just been a goof up on the thread chart

one thing i notice is that there is a ratio change between your 1236 and the 1024, there is no 11-1/2 tpi for electrical and pipe connectors on the 1024
and they gave up the 9-1/2 tpi on your 1236
 
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On my 1236 lathe I have threaded 16, 18, 24, and 28. Yesterday was the first time I tried 20. [and it isn't right, closer to 22 tpi]
What's going on?

Is it my imagination, or does the 'Thread Per Inch' chart show the 120 tooth gear to be larger in diameter
than the 127 tooth gear?

Two factors of 127/120 multiplied by 20 tpi gives 22.4 tpi.
 
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So Column 4 row C cuts 22 tpi
Looks like Colum 5 row C cuts 24 tpi. (looking at your picture on the right).
In your first post you said you had successfully cut 16, 18,24 and 28.
That means you have cut Column 6 Row C and got 24 tpi.
That seems to say that your gear box cuts the same threads in Colum 5 and Column 6 And Column 4 is cutting what is labeled for column 5.)

My guess is they hosed up the assembly of your gearbox by leaving out column 4 gears and doubling up on column 6 gears.
Take a couple scratch tests with other rows and columns and see if this is consistent.

This is the kind of thing that earns a company a certain type of reputation.

That is correct, C-6 got me 24 TPI, threaded a few flash hider 5/8x24 with this setting, C-8 for the ubiquitous AR15 1/2x28 flash hiders. C-1 setting for the AR15 tenon, 13/16x16, and C-2 for my bolt guns with 1 1/16x18.

FYI, I am not in the firearms business, I do a lot of AR barrels for our TX Juniors high power shooters.

Have not threaded any other TPI. Forgot, I did thread a couple of my bolt guns 7/8x32 for Bukys barrel tuner.
 
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