polygon thread milling... any help?

[J.bryant]

Has anyone had any experience with polygon thread milling? This is on a Muratec MD200 31i control. I know just straight thread milling would be much easier but we currently polygon mill and for the sake of not buying new mill heads we would like to try this approach first. I am trying it in G12 instead of polygonal milling but running into an 021 alarm "illegal plane select" once it starts in the first G03 move. I have changed parameter #1022 to 6 to select G17 already. I feel as I'm missing something and cant put my finger on it. I will post the code as well...
Any suggestions??


O0001 ( 750NPT_HORN )
(DWG = 750NPT_HORN)
(P-N = )
(REV = )
N10 ( MAIN SPINDLE Z AXIS MILLING OD THREAD MILLING THREAD_MILL1 )
G0 G17 G40 G80 G99 M90
M68
G28 U0
G28 W0
G28 H0
T0101 ( HORN .0714 THREADMILL-ROTARY Z )
G97 S584 M33
G0 X4.2026 Z0.3 M8
G1 G12.1 ( POLAR INTERP ON )
X4.0631 C0.5369 F25.
Z0.1
G1 Z0.0833 F0.0714
G3 X3.4431 C0. Z0.0714 R0.62 F0.0357 <<<< THIS IS WHERE ALARM OCCURS
G2 X0. C-1.7228 Z0.0536 R1.7222 F0.0714
X-3.4481 C0. Z0.0357 R1.7234
X0. C1.7253 Z0.0178 R1.7247
X3.4531 C0. Z0. R1.7259
X0. C-1.7278 Z-0.0179 R1.7272
X-3.4581 C0. Z-0.0357 R1.7284
X0. C1.7303 Z-0.0536 R1.7297
X3.4631 C0. Z-0.0714 R1.7309
X0. C-1.7328 Z-0.0893 R1.7322
X-3.4681 C0. Z-0.1071 R1.7334
X0. C1.7353 Z-0.125 R1.7347
X3.4731 C0. Z-0.1428 R1.7359
X0. C-1.7378 Z-0.1607 R1.7372
X-3.4781 C0. Z-0.1785 R1.7384
X0. C1.7403 Z-0.1964 R1.7397
X3.4831 C0. Z-0.2142 R1.7409
X0. C-1.7428 Z-0.2321 R1.7422
X-3.488 C0. Z-0.2499 R1.7434
X0. C1.7453 Z-0.2678 R1.7446
X3.493 C0. Z-0.2856 R1.7459
X0. C-1.7478 Z-0.3034 R1.7471
X-3.498 C0. Z-0.3213 R1.7484
X0. C1.7503 Z-0.3391 R1.7496
X3.503 C0. Z-0.357 R1.7509
X0. C-1.7528 Z-0.3748 R1.7521
X-3.508 C0. Z-0.3927 R1.7534
X0. C1.7553 Z-0.4105 R1.7546
X3.513 C0. Z-0.4284 R1.7559
X0. C-1.7578 Z-0.4462 R1.7571
X-3.518 C0. Z-0.4641 R1.7584
X0. C1.7603 Z-0.4819 R1.7596
X3.523 C0. Z-0.4998 R1.7609
X0. C-1.7627 Z-0.5176 R1.7621
X-3.528 C0. Z-0.5355 R1.7634
X0. C1.7652 Z-0.5533 R1.7646
X3.533 C0. Z-0.5712 R1.7659
X0. C-1.7677 Z-0.589 R1.7671
X-3.538 C0. Z-0.6069 R1.7684
X0. C1.7702 Z-0.6247 R1.7696
X3.543 C0. Z-0.6426 R1.7709
X0. C-1.7727 Z-0.6604 R1.7721
X-2.6432 C-1.1825 Z-0.67 R1.7734
G3 X-3.8213 C-0.9891 Z-0.6819 R0.62
G1 Z0.3 F75.0
G13.1 (POLAR INTERP OFF )

( PROGRAM END )
M9
G28 U0
G28 W0
M69
M30
%

 

[litlerob1]

WTFF is polygonal Threadmilling? There are Arcs expressed in the code you posted. You might have better luck asking questions, if you try not to sound smart. Polygon Threadmilling is a mechanical and functional disaster. If you want Threads that work. Or maybe you're after modern art.....

 

[wmpy]

From reading your code, it looks like you're trying to cut a 3/4"-14 NPT external thread on the centerline of the turning spindle with live tooling. I'll just assume that there's some reason you can't turn the thread and must use the live tooling.

I'm guessing that your machine won't let you helical interpolate in polar interpolation (G12.1) mode. I'm not sure if the Fanuc 31i controller will let you do this at all. There might be a parameter to turn on, or a code to allow it to happen. You can try eliminating the Z moves in your code to see if it runs like that. Of course, you won't make a good thread, but at least it will tell you if the Z move while cutting the arc is the problem.

You mentioned that the machine will do polygon milling(turning). Have you tried making the thread using that function?

What about programming using C moves while moving the X and Z?
C90. W-0.0179 U0.0011
C180. W-0.0179 U0.0011
etc.

Can you spin the live tools while rotating the main spindle in turning mode at a low rpm? Could you use G32 to move the tool along the thread?

I'm just trying to think of other ways you could accomplish this. Maybe someone else knows how to get your original code to run. Good luck.

 

[DanielG]

WTFF is polygonal Threadmilling? There are Arcs expressed in the code you posted. You might have better luck asking questions, if you try not to sound smart. Polygon Threadmilling is a mechanical and functional disaster. If you want Threads that work. Or maybe you're after modern art.....

Which is it? Do you not know what polygonal threadmilling is, or you do know and are of the opinion that it's a mechanical and functional disaster?

 

[Ox]

WTFF is polygonal Threadmilling? There are Arcs expressed in the code you posted. You might have better luck asking questions, if you try not to sound smart. Polygon Threadmilling is a mechanical and functional disaster. If you want Threads that work. Or maybe you're after modern art.....

Synchronized Thread Milling Attachment - Special Attachments & Multi Spindle Screw Machine Solutions


There are many processes out there that are not in the every day machine shops.
I'm not sure why he wants to doo this on a CNC, but maybe he is dealing with ECO-brass or other such material and it's easier to mill into millions of little chips.

With that said - I don't understand his code at all - as to how that would have anything to doo with "synch" milling....
Just looks like a single tooth V cutter.



Bryant:

I would think that synch C axis is not where you want to be for your app.

Doo you have another code that will let you run your live toys and your main spindle at the same time?
This could be a "Deep Hole Drilling" macro - intended for double live drilling for - well - deep holes...
Then you could face and chamfer the part w/o going into C axis at all, and then start C when ready to run the thread.

Example on one of my Fanuc machines (Hardinge)
M3 (4) S1000
M71 (72) S1000


Then you would want to leave the Deep Hole application, and just go into C axis mode, but not in POLAR.
Just your start X / Z / C and then your end X / Z / and your end point in C will be a high number.
In some cases C can only go so far in either direction - for whatever reason, and a 31 could be well beyond this limitation by now anyhow, but there are cases (not necessarilly Fanuc) where you actually need to start in negative C and end in positive C to get enough revolutions to complete the motion.

Another option could be to use an H value possibly? (inc of C)


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

Think Snow Eh!
Ox

 

[MLeonard]

So, for the benefit of we spectators who have never heard of this thing before, would it be correct to say that:
1) This process does not create threaded parts with a polygon cross-section :-)
2) The milling cutter has full-depth thread-profile milling teeth arranged around it in a spiral thread lead
3) If the milling cutter is rotated 1:1 with the workpiece, and slowly advanced (X-) until it reaches minor diameter, you get a fully-formed thread?

I am guessing that "polygon" only comes into it, in that there is a technique called polygon turning, in which a multi-flute cutter is spun simultaneous with the workpiece, and in that case really does yield a finished part with a polygon cross-section. The number of facets depends on the number of cutter flutes and the relative rotation speeds.

That usage has probably lent the name "polygon milling" to any process where a live tool turns alongside the main spindle, at a synchronized speed.

But I will have to admit, the first thing I pictured was also a bolt or nut with a polygonal, rather than circular, cross-section. No Loc-Tite required.

 

[Ox]

So, for the benefit of we spectators who have never heard of this thing before, would it be correct to say that:
1) This process does not create threaded parts with a polygon cross-section :-)
2) The milling cutter has full-depth thread-profile milling teeth arranged around it in a spiral thread lead
3) If the milling cutter is rotated 1:1 with the workpiece, and slowly advanced (X-) until it reaches minor diameter, you get a fully-formed thread?

I am guessing that "polygon" only comes into it, in that there is a technique called polygon turning, in which a multi-flute cutter is spun simultaneous with the workpiece, and in that case really does yield a finished part with a polygon cross-section. The number of facets depends on the number of cutter flutes and the relative rotation speeds.

That usage has probably lent the name "polygon milling" to any process where a live tool turns alongside the main spindle, at a synchronized speed.

But I will have to admit, the first thing I pictured was also a bolt or nut with a polygonal, rather than circular, cross-section. No Loc-Tite required.

I take it that Bryant's app is a single V cut slitting saw, but the one in my link does have a multi-start helix as you say, and is only intended to be fed in X.


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

Think Snow Eh!
Ox

 

[litlerob1]

Which is it? Do you not know what polygonal threadmilling is, or you do know and are of the opinion that it's a mechanical and functional disaster?

I know what a Polygon is. And I know what Threadmilling is. I know tha a Polygon is a shape. I know that Threadmilling is a toolpath. Generating a Polygonal Thread is a functional disaster. Triangular or Square shapes from a Front view just won't work. Ever heard the adage about square pegs and round holes?

R

 

[EmGo]

As littlerob points out, the name is a disaster. It's really just thread hobbing. The difference between a hob and a thread mill is that hobs have a lead, they are threaded like a screw. If you spin the hob at 90* to the part and infeed you get a wormgear, if you then traverse in z you get a gear, if you run the cutters parallel and straight infeed you'll get a worm or a thread. If they are properly synchronized, anyhow. Otherwise you get scrap

Been done for ages on gear hobbers. Not common, other ways are faster, but has been done at least as far back as the twenties. Probably earlier.

It's hobbing. Not "polygonal threading".

p.s. he link is (as far as I can tell from their description) is just a thread milling attachment. Cutters do not have a lead, they are rows of teeth. Feed in in x, feed in z coordinated with rotation the same way you would a turning tool, rotate one revolution plus a little as the cutter advances in z, back out in x and done. Same principle as a normal thread mill or multi-rib thread grinder.