[How do I?] Need help figuring out my thread chasing dial

First, make sure you have the change gears for doing 11.5 TPI threads. My lathe requires a different change gear for doing 5 3/4, 11 1/2, 23, and 46 TPI.
 
Hi Bob, setting the change gears is the easy part, that chart is simple.


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Bob Korves said:
First, make sure you have the change gears for doing 11.5 TPI threads. My lathe requires a different change gear for doing 5 3/4, 11 1/2, 23, and 46 TPI.
Click to expand...
Most american lathes have 11 1/2 on the chart, since it is our common thread for pipe, British lathes would tend to have 19 TPI since that is what they use for 1/4" pipe, they use 28 for 1/8" pipe, lathes made in Asia would have similar differences relating to their standards, deleting some that we use and substituting those that they use, regardless of the fact that they are exporting them to our or other market with different standards.
 
When in doubt, treat it like a metric thread on an imperial lathe. Engage the half nuts once and don't disengage. That way you'll never split the thread.

When I thread metric on my G0709, I start by just touching the tool to the work. Then zero out the compound and cross feed (compound is set to a 29.5 deg. angle). Then back off the cross feed one turn and move the carriage to the right of the work. Turn the cross feed back one turn to Zero. Turn the lathe on (in back gear) and engage the half nuts. No need to worry about a number since I'm not going to disengage the half nuts. Get close to the end of the thread and shut the lathe off. Mine is a gear head, so if I'm a little short, I disengage one of the speed levers so the chuck turns freely, then use a chuck key in the chuck to turn to the end of the thread.

Back off the cross feed one turn (or more depending on thread depth), reverse the lathe motor (don't touch the feed reverse lever) or turn the chuck backward by hand if you don't have reverse. Turn the cross feed back to zero and advance the compound 0.003 - 0.005" (or whatever you are comfortable with) and make the next pass.

If you are really adventurous, flip the lathe into open spindle before going into reverse. That'll get it back to your starting position much quicker. Word of caution however, don't forget to go back to back gear or the next pass will happen REALLY quickly. Ask me how I know - didn't crash my lathe but thank goodness for the foot brake on my G0709!

Bruce
 
Thanks Bruce, I had actually thought about doing it that way.

I am still curious as to how the indications on the dial are supposed to work.

Eric


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Here’s some pics of the charts on my lathe for threading, no problems setting the machine for threading, either imperial or metric.
It’s the dial that has me bamboozled.
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5bccb0c7d85d8a7ab12e600b0b494a8f.jpg
8f0469b4c6670b87d81f43aa7c6e7777.jpg
6ff58fdb70cd9ac4a2970bf10a19d19d.jpg



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Maybe I’m missing something, but I thought on any lathe with an Imperial leadscrew that no matter what the pitch is, if you close the half nuts on the same dial number to begin every pass, the cutter would always take the same track IF you have the right gears installed to cut inch threads, not metric threads.

Tom
 
I’m not sure about that Tom, maybe someone could chime in on that.

Eric


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My lathe has an Imperial lead screw and can cut 11. 5 threads but I have to treat it like a metric thread. It has a 24 tooth gear on the chasing dial, if it had a 32 tooth I could disengage the half nut
 
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