Thread cutting help

[mickri]

I practiced threading on pvc pipe to start with. This was just to learn the motor skills in doing threading. Then progressed to steel. Depth of cut has a big effect on the finish of the threads. There seems to be some mystic, almost like bragging, on how large of a depth of cut you make in any type of machining. I can see in a production shop where depth of cut is important. But in a home shop there is no prize for how fast you can machine something.

When I cut threads I start off with light cuts. Then heavier cuts. Then back to light cuts to finish the thread. How coarse or fine the thread is also has some bearing on the depth of cut. Very fine threads require a pretty small depth of cut.

Practice, practice and more practice helps to get better results.

 

[Just for fun]

Thanks for all the replies guys and the links.

I did look again in my hand book, and by golly it does have some metric info. Geez, I should have look a little furture.

Here is a full on photo of the threads. I do realize this is only my second attempt and practice will make all things better.

 

[benmychree]

All any thread has to do is fit the nut or tapped hole; in using a nut to fit a thread to be cut, I run a tap through it to clean out any burrs, etc.

 

[brino]

Your threads seem to have a "double peak" like the ones we saw recently here:
https://www.hobby-machinist.com/threads/threading-problem.98780/post-933853

Perhaps reading that could be some help too.

Maybe just a burr being pushed-up and rolled over?

Brian

 

[SLK001]

Agree on the "double peak". In threading metric threads, usually you don't disengage the half-nuts once you start, but make one pass, pull out of the cut, reverse the lathe to reset the carriage, then add to your last cut and make another pass. Clean up your work with a wire brush to clean out all the remaining swarf in the threads - it won't help on the double peaks, but it will make your threads look nicer. I also run a triangle file in the threads to smooth out the flanks, then run a flat file on the peaks.

 

[Just for fun]

That one is just standard 1/2 - 20. The only reason I brought up metric is I need a metric stud or all thread about 60mm long and thought that might be something to practice on.

I can see where it might be better to practice on US Standard stuff to get in the habbit of engaging the half nut at the right time.

 

[Just for fun]

I did engage the half nut in the wrong place right off the bat.

 

[mikey]

Tim, what kind of tool are you using? Can you show us a pic of the tool and your set up on the lathe?

Also, how are you determining that your threading tool is at center height?

 

[brino]

I did engage the half nut in the wrong place right off the bat.

Okay, one problem identified; that's easy to fix!

Now just some other minor tweaks to fix the raggedness.......tool and centre height (as Mikey mentioned), speed, lube, material, depth of cut.

As I said in the other thread, your first single point threads are better than mine were.
It will all come together!

Brian

 

[Just for fun]

Here are some photos of my setup, I did find that the tool post holder was not square to the chuck...... I thought I had checked that.