Cutting a 3/4"-10 Class 3A Thread in Aluminum

[seal killer]

All--

Here is my next threading project. The goal was to turn a 3/4"-10 class 3A thread in aluminum. However, I have no way of verifying that it is indeed a class 3A thread. The basic diameter was 0.7500".

I enjoyed turning it, as Harold suggested one might in another thread. Of course, I am in the learning phase and would sincerely appreciate your comments as to how I might improve. Here is the YouTube video and a photograph of the finished product.

--Bill

[GlennW]

Hello Bill,

Nice looking thread!!

The next step would be to purchase a set of Pee Dee wires for measuring the threads using the three wire method. This would be a way to determine if the thread is to spec or not as far as Pitch Diameter.

Fisher Machine Products, as well as others sell them.

http://www.fishermachine.com/index.php? ... ucts&cat=9

[Jose Rivera]

Agree with the 3 wires. Is all I've ever used unless there were thread mics available.
The class 3 requires for .750-10 NC calls for pitch diameter range of .6895" to .7126".

Just finish it by just running the nut wont cut it if the tread needs to be to spec.
The noted diameter can only be measured with 3 wires or a thread mic.

And to finish it correctly, the nut should be a class 3B nut, or checked with a .750-10 threads Class 3B thread ring gage.

Bill, you've done great and you come up a long ways from mill work only.
My comments of course are if you are needing to do something to spec.
There need to be a linear play (movement longitudinally between both parts) this is needed to keep dirt from galling the nut.
Di-similar metals can be a bitch and can gall easy. Almost best to have a sloppy fit, with moderation.

Don't expect that every type of metal will pull a chip as nice as what your video show. Some alloys are a bugger to thread.
Stainless can work-harden very easy. Applying more pressure to the tool because is not cutting could all of the sudden dig-in and mess the job.

Well done video, you must be having fun !!

[Andypullen]

Agree with the 3 wires. Is all I've ever used unless there where thread mics available.
The class 3 requires for .750-10 NC calls for pitch diameter range of .6895" to .7126".

That's an awfully wide range for a 3A thread jose..... .023"???

Recheck your Machinery's Handbook.

Ditto on PeeDee thread wires. I have 2 sets

Andy Pullen

[Harold_V]

Agree with the 3 wires. Is all I've ever used unless there were thread mics available.
The class 3 requires for .750-10 NC calls for pitch diameter range of .6895" to .7126".

That's off the mark, Jose, assuming you're discussing a 3/4-10 3A unified thread. The correct pitch diameter for that size is .6850"/.6806". For a class 2 American Standard thread, same size, PD would be .6850"/.6786"

Harold

[Harold_V]

Very well done, Bill.

A tip.

When you thread to an undercut, it's wise to practice retracting the cross slide (not the carriage) as you disengage the halfnuts. Do it even though it isn't necessary, as it builds the skills you need when you must do so. It should happen as a smartly executed coordinated movement. I generally watch the edge of the tool as it approaches the shoulder, then pull out when I'm in the same proximity with each pass.

If you must thread a given distance, with no relief, you can put a pencil line on the part and retract when the tool hits the line.

Harold

[seal killer]

Harold--

Very well done, Bill.

A tip.

When you thread to an undercut, it's wise to practice retracting the cross slide (not the carriage) as you disengage the halfnuts. Do it even though it isn't necessary, as it builds the skills you need when you must do so. It should happen as a smartly executed coordinated movement. I generally watch the edge of the tool as it approaches the shoulder, then pull out when I'm in the same proximity with each pass.

If you must thread a given distance, with no relief, you can put a pencil line on the part and retract when the tool hits the line.

Harold

When I cut a previous thread that did not have a sufficient undercut, the lack of practice moving the cross slide at the correct time became very obvious. Thanks for the suggestion.

--Bill

[GK1918]

Not enough undercut, no problem, when its time to terminate the tread , knock off the half nut
and just let her spin a few times, it then forms a termination line, then back off the cross slide.
You got it, good job, then after you do a couple zillions, no need for wires, thread mics its all in
your fingers. The real secret is spring cuts and a few to get that feel. I have wrote so many
times as why people are not using a thread stop theres no shame, its just way easier because
it puts some tension on the crosslide, gets rid of backlash or gib issues always gets you to
-0-, one less thing to worry about. And also dont get to concerned about terminology, uncertain,
call it a thingy who cares, its the job that counts and you did a good one.

[Harold_V]

Not enough undercut, no problem, when its time to terminate the tread , knock off the half nut
and just let her spin a few times, it then forms a termination line,

While that sounds like a good solution, it isn't a good idea. If you're creating a large thread (fast pitch) it gets difficult to release the half nuts at precisely the same place each time. That often results in a broken threading tools. Retracting the tool via the cross slide helps limit that problem, and does not create stress risers in the way of a sharp circular undercut. The typical design of a thread relief provides radii in the two corners, for that reason.

Beyond that, it's not good practice. If no thread relief is permitted, one should not be created. I'm speaking, of course, for those who work to prints, where one does not have the luxury to re-engineer the design of a part. For the home shop guy, making items for his own pleasure, that may or may not apply, but it does no harm to learn good and acceptable shop practice. By doing so, one gains the necessary skills so operations that can be tricky are already known and can be exercised without issue. The same thing applies to knowing and understanding proper terminology, so intelligent conversations with those who are so gifted become possible.

Harold