[cvmachinist]

Our unique threads must have a thread start that begins by directly feeding into material at the start of threads. We currently use two lines of g76 code. Problem is, when I slowed things way down, I realized the lathe was actually doing a rapid move only in "x" before beginning the threading in "z." So, in other words... the the first p010060 did not make the machine do a 30 deg walk down feed into the start of threads, like the books say it does. It merely moves a certain incremental amount in "z" with each subsequent pass. Like a staggered start, instead of an angular start. I'm thinking maybe this is a parameter setting, or perhaps, there's another way to program this so I'm not breaking threading inserts due to the rapid move?

[fordav11]

Normally threads need to start outside the material because it rapids into the part as you have discovered. And also because starting a thread in the middle of the part would not allow anything to be screwed onto the part.

If you make the depth of cut smaller the rapid will not cause insert damage. You can run the rapid at 50% or 25% and the thread will work fine. Just the rapids back to start point will take longer.

You can program each pass with G92 or G32. That will give you more tool control but it will make the program very long.

[cvmachinist]

Our threads are one directional, and are designed to screw in to a shoulder, and stop. Thereby necessitating the thread start into the material. How would a G92 help in controlling this? Could I add an angular start, or feed into the material before start of threads? I was under the impression that a G92 was just a drawn out rectangular threading cycle not much different than a G76.

[zooloader]

why not put an undercut (groove) at the start?
what is a "one directional" thread anyway?

[fordav11]

if you thread starting into the material without any Z clearance you'll end up with a groove there anyway
seems like a very strange application for a thread.

[txcncman]

Probably another engineer trying to be a machinist?

[cvmachinist]

We did over 4 million in sales last year selling products with this thread design. While it is unique, it is also ingenious

[fordav11]

ah! top secret stuff......
well if you can't give us more info on the application you'll probably have to figure it out yourself.

txcncman: yeah all of our engineers are like that at my work. they love to create things on paper that are almost impossible to produce. we end up making it anyway at a massive development cost and the product ends up not very good.
Then the management wonder why profits are down......

[cvmachinist]

A little thread start clearance move before the start of the thread did the trick. This also enabled me to take much fewer passes, since I'm not slamming into the material between passes. Thanks for your input.

And... yes... it's top secret stuff. And I've made some of the most complicated threads here you could imagine. And our tolerances are pretty crazy for threads also. Try + or - .0005" on thread minors.

[txcncman]

I cut oil field/API threads for years. I can't imagine any other threads could be more difficult.

[fordav11]

I cut API threads too. Pain in the ass toleranced stand-off with ground gauge.
10:1 taper ratio means movement of 0.001" in X takes 0.010" in Z (decreases the stand-off by 0.010").
The stand-off tolerance is +0.010" - 0" but that's only 0.001" in X.
To take 0.001" in Z means you have to take 0.0001" in X..... basically impossible.

[cvmachinist]

Without getting into details, we have a triple thread. Left and right hand threads timed together. There are over 100 mating surfaces on one part. Getting everything timed and adjusted correctly is quite a challenge.

[underthetire]

Hehe, your very close to me! If you really get snagged, Talk to Henry at your local Ellison office. One of the smartest programmers i've ever known.

[txcncman]

Sounds almost like the stacker/unstacker shafts we used to make. Right hand on one end, left hand on the other. Had to clock each end within a couple of thousandths, not degrees, inches, along the axis, so that the thread starts on each end would match. Fun stuff.

[cvmachinist]

Sounds similar. This has a third thread down the middle of the other two for chip relief when tapping the holes. We make the matching taps on a swiss machine. Very difficult to measure also. But, hey... we're machinists. We can do anything.... haha