A lesson on thread cutting....

In a perfect world, you would make at least a GO nut that is right on nominal for that size. Mark it and keep it for next time.
 
The first thing you should learn when threading is to properly set up the correct pitch, setting the tool bit and compound to the correct angle. The second thing you should learn is to reacquire the thread if the need to remove it arises. I always check it even if I'm turning between centers. You do not need to set the compound to 90, leave it where it's set so you are not changing it back and forth if you need to thread another piece. It's just a matter of moving both cross slide and the compound until the thread is reacquired. When making both outside and inside threads I always make the external first as there are abort 3 times as many ways to measure the correct PD on an external thread as compared to internal threads. I've said it before and will again that using one wire is a lot easier and the accuracy is not deteriorated especially for the hobby machinist.
 
A side note: is there an equivalent to external thread wires for internal threads?

I have been in the OP position many times with external threads until I acquired thread wires. It has helped minimize the error, but only for external threads.
 
Another good tool for the job is a thread comparator micrometer, it has two angled points, it does not measure pitch diameter, but does compare a thread being cut with the old part; they are much cheaper than thread mikes. Back in the day, we used OD calipers with the tips ground down to an angle of less than 60 degrees to achieve the same result.
 
When I need to cut internal threads, I generally make a plug gage if I do not have a part to try the thread as I cut it. In effect, I make my own "go" gage.
 
I had to make go no-go gauges for some instrumentation tools at 72 TPI. Otherwise they had to be mated for life, once the gauges were made all the parts were interchangeable. Thread depth was around 8 thousandths.
 
After reading the above posts, I realized what mistake I made in cutting the remainder of the threads. Like they say "Live and Learn, But listen to the guys on Hobby Machinist and save yourself some time"
Thanks for all the info,
Eric
 
Downunder Bob said:
Ah thread files, a beginner's best friend.
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I used one just yesterday to help out a client on site. I did not have 3/4-16 die nut,bit do have a thread file with 16tpi and it did the job and the client was happy, that's all that matters.
 
Mitch Alsup said:
It was either Abomb79 or Keith Fenner (on Youtube) that showed how to use the compound to reacquire the thread. Basically, you set the compound 90º to the cross slide. ...
Click to expand...

It was an Indian YTer I saw doing that.

While it's easiest to pick up the thread again with the compound at right angles, you can certainly do it with the compound at a more chatter friendly angle. You just need to remember that the compound moves in both X and Z.

Start out with the tool tip just outside the threads and the compound about 1/3 of the way in. Half-nuts must be engaged for the entire procedure. Adjust the compound to align the tip of the tool with the center of a thread by eye, and then advance the cross slide until the tip nests into the thread. If it isn't aligned quite right, back out the cross slide, adjust the compound, and advance the cross slide again.

Once it nestles nicely in the thread, zero the dials and resume threading.

Sent from my Pixel XL using Tapatalk
 
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