[How do I?] Do 20 TPI

Bamban

Bamban

Active User
H-M Supporter Gold Member
Joined
Jul 13, 2014
Messages
1,051
On my 1236 lathe I have threaded 16, 18, 24, and 28. Yesterday was the first time I tried 20. Since I have threaded on the same "C" gear of the L side of the QCGB, I just grabbed the "4" gear on the R side for the 20 TPI. When I got close to the point I needed to check the thread with the barrel extension, it will thread about 3 turns and stop. I grabbed the thread gauge and it not not match the 20 TPI

Is the gear in "4" position not right, the "C" position on the L side must be correct since I have threaded 16, 18, 24, and 28 with no problem.

Here is another kicker, my 1024 has the data plate for threading and the side gears are the same, but I was able to thread 20 TPI with it with no problem.

What's going on?



20170924_210044.jpg 20170924_205330.jpg 20170924_205255.jpg 20170924_205337.jpg 20170924_205751.jpg 20170924_205308_001.jpg
 
C 4 position looks right to my eyes. When I have the correct thread position and the item only partially goes on it has been due to the depth not being sufficient. Normally a few thou extra to remove then it threads. If you have thread wires you can measure the depth of the threads.
 
It confuses me that the charts show a metric end gear setup for both inch and metric charts; for inch threads the spindle and QC box should mesh with an idler in between, not the compound gear train shown.
 
Dave Paine said:
C 4 position looks right to my eyes. When I have the correct thread position and the item only partially goes on it has been due to the depth not being sufficient. Normally a few thou extra to remove then it threads. If you have thread wires you can measure the depth of the threads.
Click to expand...

I kept on cutting till the pitch diameter measured with PD Mic was way below, no go. Based on 13/16 x 20 TPI I threaded on the 1024 I have pretty good idea at what point do I check for fit with the barrel extension. The 20 TPI thread gauge will not mate with the threads.
 
benmychree said:
It confuses me that the charts show a metric end gear setup for both inch and metric charts; for inch threads the spindle and QC box should mesh with an idler in between, not the compound gear train shown.
Click to expand...

I threaded many 16, 18, 24, and 28 TPIs with the same gear set up as is, and using the QCGB according to the template with no issues. My 1024 has the same set up and I threaded 20 TPI with it with no issues.
 
Bamban said:
I threaded many 16, 18, 24, and 28 TPIs with the same gear set up as is, and using the QCGB according to the template with no issues. My 1024 has the same set up and I threaded 20 TPI with it with no issues.
Click to expand...
What setup are you using on the end train? simple or compound?
 
benmychree said:
What setup are you using on the end train? simple or compound?
Click to expand...

Sorry, not sure what "end train" and "simple or compound" mean as they relate to threading. If the question pertains to cross slide or compound when threading, in this particular job, I opted to use the compound, however, utilizing the power and feature of the VFD, I thread with the halfnuts engaged, at the end of the threading, stop the spindle, using the cross slide retract cutter, and hit the reverse and hit stop once cutter is past the workpiece. Start threading procedure again.

The side gears have in there since I got the lathe, the 2 gears with 40 teeth have in use in threading 16, 18, 24, and 28 with no issues.
 
Last edited:
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. Then you throw columns 3, 4, and 5 at us with 4 3/4 to 10? I'd have guessed 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
 
Last edited:
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.
 
BGHansen said:
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
Click to expand...
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.
 
You must log in or register to reply here.
Back
Top