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Single point threading - order of operations

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steve_p

Aluminum
Joined
Mar 5, 2014
Location
Southeast Massachusetts
When single point threading with a non-full-profile insert, what is the best order of operations?
Should I turn to final od, then thread?
Or rough turn oversize, thread, then finish turn to proper od?
Some other method I haven't mentioned?
I am new to threading on the lathe, so any input is appreciated.

Thanks,
Steve
 
Turn the OD, then thread. You do NOT thread full profile/full depth at one shot. You really need to do some reading about the subject before attempting this or one of the following will happen:
1) You'll trash the workpiece
2) You'll trash the cutting tool
3) You'll injure yourself
4) All of the above

Do some homework on the subject then report back here what your procedure is going to be including ALL the details of the piece you intend to create. When you post a question (that's ok) you need to include the material/intended use/class of fitment/machine you intend to use/tooling you have.
 
steve_p said:
When single point threading with a non-full-profile insert, what is the best order of operations?
Should I turn to final od, then thread?
Or rough turn oversize, thread, then finish turn to proper od?
Some other method I haven't mentioned?
I am new to threading on the lathe, so any input is appreciated.
Click to expand...

Yes, you should turn the OD first. I always turn the OD minus .005 under.
For example, turning a 1/2-13 thread I would turn the OD to .495 rather than .500. This gives some clearance between the stud and the nut.

If you are new to turning threads I suggest you place a groove at the end of where you want to stop the thread. What I mean by that is to put a groove in your material (I use a cut off tool for this groove) at the end of the thread and make this groove the 'minor diameter' of that thread.
This groove does 2 things........ It gives you a 'run out space' so you do not crash the threading tool into the stock and when the tool cuts deep enough to touch this minor diameter, you need to consider the thread as being at the correct depth.
The 'minor diameter' is simply the OD minus the depth of thread (times 2).

As AD Design said, it will be a great help to you to do a little reading before you get into actually making threads.
And of course this site is the best place to find answers to your questions.
pg
 
Sorry for the lack of detail.
Part is a simple threded bushing, made from 6061 aluminium.
Thread is 1"-20.
I don't have a spec for thread fit, this is an adapter for a work stop in my hardinge flex-c collet chuck. I would say probably a 2a thread.
I turned to final od, then threaded to depth in 6 passes, including 1 spring pass.
The major diameter seemed "rough" die lack of a better description. Hence why I wasn't sure if I needed a finish turn pass after cutting the threads.

Machine is a haas st20y. Turning tooling is iscar.
 
Yes that roughness is common when you're not cutting full form. Get some wet and dry and rub it. Cutting the diameter after threading creates tiny burrs in the v of the thread which make it seem tighter than before but you can just run the thread cycle again if you wish, also depending on what material it is you can damage inserts from all the interrupted cutting.
 
Here is what I get for turning a 1 inch-20tpi thread:
Major Diameter = .495
Minor Diameter = .4242
Depth of thread (times 2) = .0758
Compound rest set at 29°
Advance the compound .0860 to cut the thread to the proper depth.

Roughness of the outer diameter of the thread sounds like you do not have the threading tool at right angles to the stock and/or you do not have the compound set at 29°. Setting it at 29° allows the tool to 'clean up the cut' on the backside of the threads.
Also when turning aluminum I use WD40 sprayed over the thread every time I make a pass.

The above is how I would cut this thread on my South Bend machine.
pg
 
You need to pass some emery cloth on the od to deburr the threads or you can rough turn the od about. 002 bigger. Thread then finish turn and run the thread cycle again except for the 2nd thread cycle tell it to do your first cut at full depth and put the finish amount at 0 so it just does one pass. After all that you should have burr free threads. Sand it or program it.
 
yardbird said:
Yeah, 20tpi only roughly .05 deep


Brent
Click to expand...

Excuse me?
.050 is not the depth of thread for a 20 tpi, but rather .050 is the PITCH of that thread.
The single depth of thread is .0379 and since we have two sides to the stud the double depth of thread is .0758, as I stated before.
Sorry, I have cut too many threads in my life to do this any other way.
pg
 
drewboyer said:
You need to pass some emery cloth on the od to deburr the threads or you can rough turn the od about. 002 bigger. Thread then finish turn and run the thread cycle again except for the 2nd thread cycle tell it to do your first cut at full depth and put the finish amount at 0 so it just does one pass. After all that you should have burr free threads. Sand it or program it.
Click to expand...
Thanks for the tip.
Steve
 
Ok yeah lol.. I see now my mistake i thought you ment .078 x 2 and that seemed like a lot. Sorry, peace brother...


Brent
 
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