3 tries and 3 fails to make a 1/4 20 thread - part 2

[Nigel123]

The chart I posted is right out of the How to Run A Lathe booklet from South Bend, so it will work for all SB lathes out there. I'm not positive that it will work for other lathes from other manufacturers.

I reworded some of the text to make it clearer (for me) to understand.

I printed out the .pdf version, took it down to Office Depot and had it laminated, then posted it above my lathe.

Did a little investigating this morning and found out SB lathes move the carriage 4 ins per revolution of the dial
My lathe only moves 3 ins
Thought they were created equal was wrong

 

[Nigel123]

They do show settings for fractional threads the chart is mounted on the dial housing
I have threaded fractional a few times they turned out okay
Maybe I will try to cut an even number of threads using any of the 8 lines and see what happens(tomorrow)
Will let you know how it goes

Does not work different travel per revolution of dial indicator

 

[ErichKeane]

Heh, when you confirmed in the other thread that you'd had the compound at the wrong angle, I was quite surprised! A bad compound angle almost ALWAYS looks like the threads in this thread, not as a double-start. The last thread you likely had the compound right, and were just not starting consistently in the same engagement.

Note that with an 8TPI lead screw, every OTHER engagement works for 20 TPI. So I was positive in the other thread that it was the problem

There is a couple of people who do pretty good videos on starting threading that explain the 'why' of the compound angle that makes it quick to visualize whether your angle is right. It is just-shy-of 30 degrees from 'straight' as the operator stands.

For some reason the Chinese lathes have the wrong 0, which I don't really understand.

 

[twooldvolvos]

Heh, when you confirmed in the other thread that you'd had the compound at the wrong angle, I was quite surprised! A bad compound angle almost ALWAYS looks like the threads in this thread, not as a double-start. The last thread you likely had the compound right, and were just not starting consistently in the same engagement.

Note that with an 8TPI lead screw, every OTHER engagement works for 20 TPI. So I was positive in the other thread that it was the problem

There is a couple of people who do pretty good videos on starting threading that explain the 'why' of the compound angle that makes it quick to visualize whether your angle is right. It is just-shy-of 30 degrees from 'straight' as the operator stands.

For some reason the Chinese lathes have the wrong 0, which I don't really understand.

ErichKeane. Thanks for your input. Correct me if I am wrong but I am using a South Bend 10k for which I measured about 8 threads per inch on the lead screw. So using the information from the "How To Run A Lathe" book, I can engage my half nut on any of the 8 lines or 1/8 revolution for all even TPI. Your reply seems to say that I should only engage on every other line for a 20 TPI which is even. Can you clarify?

 

[ErichKeane]

ErichKeane. Thanks for your input. Correct me if I am wrong but I am using a South Bend 10k for which I measured about 8 threads per inch on the lead screw. So using the information from the "How To Run A Lathe" book, I can engage my half nut on any of the 8 lines or 1/8 revolution for all even TPI. Your reply seems to say that I should only engage on every other line for a 20 TPI which is even. Can you clarify?

I don't know much about your thread dial/leadscrew, but what I'm saying is you can engage every other 'engagement point' on the leadscrew (as you discovered, you can engage between lines as well!).

The relationship between that and the lines on the leadscrew are going to depend no the machine you have, but you can likely count how many leadscrew rotations it takes to get the thread dial to go around 1 time, and reverse it from there.

 

[ErichKeane]

Note, I found this manual for a 10k (no idea how old your machine is, so no idea if that is too new) that shows: https://cdn0.grizzly.com/manuals/sb1002_m.pdf on page 50 that every other 'line' works for 20 TPI. You likely need to find that chart for your machine, or simply use the same line everytime.

 

[DavidR8]

From the "How to Run a Lathe" book:

 

[twooldvolvos]

Note, I found this manual for a 10k (no idea how old your machine is, so no idea if that is too new) that shows: https://cdn0.grizzly.com/manuals/sb1002_m.pdf on page 50 that every other 'line' works for 20 TPI. You likely need to find that chart for your machine, or simply use the same line everytime.

Thanks, ErichKeane. That helps. My lathe is from 1973. The engagement points for laths seem to vary widely depending on which lathe you have. Even laths that are named the same vary greatly. My 1973 South Bend 10K seems to be much different than a new South Bend 10K.

 

[SLK001]

My 1973 South Bend is 10K seems to be much different than a new South Bend 10K.

New 10K? If you're referring to the one Grizzly sells, it is just a Taiwanese model with a South Bend sticker slapped on. As for true SB 10K's, the basic operation was the same from day 1 until the end of production. Every SB lathe produced from the 1920's on used the threading dial information that I posted earlier. Now OTHER BRAND lathes may or may not conform to those standards.