Thread Rolling - CNC Machining - Practical Machinist

We have M4 external threads about 1" long to cut/roll/form on the ends of 5/16" 303 stainless steel rods.

One of the things we tried was rolling the threads.
We got an A01 Axial head from RSVP tooling.

It can only adjust down so far, but not far enough to get the root of the thread deep enough to gage properly.
It can be re-assembled to push the rollers smaller, so the threads gage OK at the end of the rod.
However, once it is re-assembled to pinch the rollers tighter, the threads are too extremely tapered as they get to the shoulder.
The threads are supposed to go up to a shoulder.
The guage will only go to about within .200" of the shoulder.
The rollers should only have a lead of about 2-3 threads, not .200" of lead to them.


This makes NO sense to me. I can send the unit back, but they will send it back to the factory.....
All the way to England..
I have HUNDREDS and HUNDREDS of parts to shove out the door...NOW ! No time to wait for all of that.

Can anyone offer any insight on what could cause the extreme taper/lead on the thread rollers?
Any ideas of what to look for?

Let's limit this thread to the thread rolling problem....
Another thread can go all over the place about trying to Cut the threads..


..........

I brought this up before, while I was trying to cut the threads.

Since then we have got in new turning tools, and new Carmex threading tools.

Turning the rods down and threading them is possible.... But a true nightmare.
They will eventually run OK, for maybe 25 to 100 parts if you are really lucky, then there will be enough variation that they will be too shallow on the very end due to deflection... you can adjust the parameters, until it works again, for a while...


Since the deflection is so great we actually tried several thread passes, some straight on for the basic threads, and some with more taper for the end of the thread to defeat the taper and deflection of that long and slender rod...

Since the tools wear ever so slightly, and the amount of taper is so very dependent on the amount of wear, they will not stay running for very long, before it stops working, and you chase 20 parameters around getting "just the right amount" of taper to make good parts... I remember the thread stating that you were single pointing them and I was

I am very surprised that you had that good'a luck!

If I recall correctly - you said that this was one of your first jobs on a CNC lathe and that it was running OK. And I mentioned that if you had more experience you would have never attempted it.

(Yes - I attempted similar at one point as well.)
They say that good judgement is a product of experience.
Experience is a product of bad judgement.
(or something like that..) (measure once - cut twice?)

ANYWAY....

I went'n looked to see if I had a head that went that small, and I don't.

I doo not understand the issue that you are saying.... You should be able to almost set your GO ring right up to the shoulder. (almost)

Is your blank size small enough? = Are you overfilling the rolls near the shoulder?
(would not seem likely, but...)

Are the crests of the rolls in good shape?
I know that 304 will wear them down kind'a quickly. Not sure on 303.
Doo you know if you got cobalt rolls for SS?
If by chance your crests are worn, you can (at least on Fette heads) you can flip the rolls over and use the other end, but you really need to stop and think about how you install the rolls. You need to flip #2 and #3 around to keep pitch start positions in time.

I don't understand re-assembling the head to give a differ'nt helix?
Don't think that is possible on any heads that I have.
That feature is usually integral with the main head plate.

???

I would think that RSVP would know what they are dooing tho....

It almost sounds like M4 is actually just beyond the capacity limits of the head.
Like trying to run M6 on my 1/4"+ unit eh?


I dare say - I too would be trying to stuff a round adjustable die in there and drive on!
That should run good in 303!
I would recommend some sorta float mechanism for your holder tho.
Doo you have RIGID tapping?
If not - the die gets to be a bit more dicey....


--------------------------------

Think Snow Eh!
Ox The blank size is consistent all the way to the shoulder.
I do not have RIGID threading.
The rolls have been reversed, and reversed again..
Same results either way.
The crests on the rolls do not look worn out. Under 20X microscope.

It is as if the thread rolling head only holds the rolls tight enough at the base, but not at the front of the roller head.

The rolls do go right up to the shoulder of the part. But they do not pinch hard enough to roll threads on THAT end of the rollers.
The BACK end of the rollers is pinching tight enough to make threads deep enough for the guage to fit into.

The thread rolling head is adjustable.
If you go outside the adjustment range, you can take it apart, and re-assemble it to move the adjustment range.
There are three studs to hold it together.
The cam plate that moves the rollers has seven splines on it.. (refered to as the "center gear")
So you can assemble the cam plate as from the factory, or plus or minus three or four positions to change the range of the cams that move the rollers.
Once I move the cam plate ( center gear) to another position, the rollers are only pinching on the back end of the rollers.
The pins that carry the rollers are tilted slightly to account for the pitch of the threads. I can only guess that adjusting them too far gets the relationship of the pitch of the threads to the tilt of the pins (know as the "eccentric spindles" ) so that the rollers are tilted outward in front, and inward in the back, and thus only rolling the threads in the back end of the rollers.

I tried real hard to explain that over the .... But somehow could not explain it..
Leaving the only option to send it back to the factory... But no longer any time to do that...

Did I mention we did more work in the last month than in any previous year?
We seem to be in a coast mode right now, with only 5,400 (seriously!!) parts scheduled into the Robodrill in the next three weeks.... !!!!
No time to think or blink....

Yes, I have made 's of these confounded parts..
Just a few at a time with a single point tool, before I have to start over chasing the tapers...
This is the same part that gets the TORX broached into the other end.
That end works great. (oops! did I say that out loud?)