Hello Guest it is May 25, 2019, 09:48:49 PM

Author Topic: HOW TO PICK-UP A THREAD - CNC THREADING  (Read 6108 times)

0 Members and 1 Guest are viewing this topic.

Offline RICH

*
  • *
  •  7,334 7,334
    • View Profile
HOW TO PICK-UP A THREAD - CNC THREADING
« on: July 21, 2008, 10:03:10 PM »
Hi All,
How do you pick-up a thread and re-run a threading program to take a few more passes over the threads?
The piece is already done, removed from the chuck and of course the motor was stopped.
The CNC lathe has a single slotted disc and steppers. Just need some general guidance if it's even possible.

I have no problem doing this on my manual lathe. Just never had to do it on a CNC lathe.

RICH
Re: HOW TO PICK-UP A THREAD - CNC THREADING
« Reply #1 on: July 21, 2008, 10:13:18 PM »
Now THAT is an interesting topic. I'm anxious to see if and how Mach can deal with it, as well as a conventional production machine with the electronic "Gearing" between the C and Z axis's.
You come up with some good ones RICH.
RC

Offline RICH

*
  • *
  •  7,334 7,334
    • View Profile
Re: HOW TO PICK-UP A THREAD - CNC THREADING
« Reply #2 on: July 21, 2008, 11:35:37 PM »
RC,
We can do this, kind of, in another program because the Z axis movement is slaved to an high resolution encoder for position when threading. ( hope the encoder use becomes a reality with the SS ) In fact, we stop the program from running, then turn off the motor, and then can turn the sherlines spindle by hand and remove burs etc. even allowing the crazy 0-80's or smaller to be cut just right.  Now I know you can't do this with a big lathe but works kind of nice with the little lathe.

My friend called me since he had overcut a piece and just didn't know how to recut the thread without ruining it.
Of course my answer, after an hour of discusion, was to make another piece, maybe under this time!
RICH

Re: HOW TO PICK-UP A THREAD - CNC THREADING
« Reply #3 on: July 21, 2008, 11:59:11 PM »
I see... what you have there is basic electric gearing between the Z and C encoders.....like the "Big Boys" do.
From what I gather, Mach is incapable of this, even if there were encoders attached. I cant imagine how picking up the thread can be done in Mach, other than by trial and error. Run the G76 slow enough to see where to set the Z starting point, then creep in.
Would take some time....but might salvage a valuable part.
Cool stuff,
thanks, RC

vmax549

*
Re: HOW TO PICK-UP A THREAD - CNC THREADING
« Reply #4 on: July 24, 2008, 10:16:14 PM »
Rich you do it about the same way as you would on a manual setup. Return the piece to the chuck and set up. Then move the bit slightly above the thread and start a thread pass and see how it lines up. THen ofsett Z a touch and rerun, etc until you have it running dead on as best you can see. THen reset the bit and make a test cut. Most times with a little patience you can get it dead on.

UNLESS you are threading up to a shoulder then it gets tough. YOu would then have to rotate the stock in the chuck bit at a time to try and time the stock back in.

Just a thought, (;-) TP