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Author Topic: G76 threading issues - any thougts?  (Read 15948 times)

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G76 threading issues - any thougts?
« on: March 16, 2013, 06:24:42 AM »
Hi,
I am using the simple threading wizard to try and cut a 32 x 1.5mm thread on my Emco Compact 5PC (modified to Mach 3).

I have had a number of problems that appeared to be associated with the X infeed missing steps. When running the code generated by the wizard, I can hear the X attempt to get close to the thread OD then there are a couple of missing step sounds and then the thread is cut at an indeterminate depth.

Looking through the generated code based around G76, it appears to be in line with what I was expecting:
G00  X22
G00 Z3
G00 X16
M03 S200
G76 X13.9 Z-16.5 Q10 P1.5 J0.05 L45 H0.05 I29 C6 B0.025 T0

I have tried to read all of the threads (sorry ;D ) but there appear to be none with similar problems.

I then edited M1076 to give me the full code and that is where I start to see what may be a problem - but no idea why:

(Min decremant being used)
(Decrement = 0.05 pass 2)
G01 Z3
G32 X15.9 Z2.9446 F1.5
G32 X15.9 Z-16.3125 F1.5
G01 X22 Z-16.5 F1.5
G00 X22 Z3
G00 X16

The underlined G32 is the key issue I think; Z is set to 3 followed by an instruction to screwcut to 2.9446, followed swiftly afterwards by the 'real' G32 to do the thread I need.

So.....:
  • what am I doing wrong.....? Is this something I have set/not set in the wizard or is this something that is caused by 'something' else?

If I edit out the 'odd' line, then the threading is successful.

Both files attached in full in case there is something else buried in the files.
Rev is 043.062, using MSM v2.0 and the wizard is shown as 1.7

I know that threading is always a difficult issue but this has me very confused.

Simon

Offline Hood

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Re: G76 threading issues - any thougts?
« Reply #1 on: March 16, 2013, 07:43:43 AM »
Dont see why that would cause an issue, maybe try your start further away, say Z10 and see if that helps.
Can you attach your xml if that doesnt help
Hood

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Re: G76 threading issues - any thougts?
« Reply #2 on: March 16, 2013, 07:56:42 AM »
Simon,
I don't use MSM and there are posts  that 062 has problems. So not sure where the culprit may be.
I never had problems with using either the M1076 for output based on G76 or G32 and frankly only modify the M1076  for G32 output and nothing else.

One thing that a user should do is always click the button, in the wizard , check the "calc number of passes" as that will tell one if the acceration or velocity exceeds
user configuration based on selected rpm. Not sure what MSM does.

RICH

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Re: G76 threading issues - any thougts?
« Reply #3 on: March 16, 2013, 08:00:36 AM »
Per Hood's reply,  the start should be 3 to 5 pitch lengths away (general rule of thumb) and there is nothing wrong with it even being longer.

RICH
Re: G76 threading issues - any thougts?
« Reply #4 on: March 16, 2013, 10:10:20 AM »
Hood, Rich, thanks for your responses.

Rich, I couldn't find anything about 062 issues on threading - but I am probably not looking hard enough...

My biggest issue at the moment, and the thing that I think is causing he problem is the snipped bit of code in my first post which contains TWO G32s, one directly after the other.
I understand that G32 requires a move to X and Z prior to the G32 itself
The output from the wizard gives a Z move followed by an initial G32 going all of 0.05mm fixing X I guess, then the proper G32.

I feel my lathe cannot cope with the initial G32 followed by the 2nd one
Or am I barking up he wrong tree....?

Simon

I also tried setting the Z much further away initially with the settings (Z clearance) which didn't seem to do anything and then directly moving the start to Z to 10.


Offline Hood

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Re: G76 threading issues - any thougts?
« Reply #5 on: March 16, 2013, 07:33:29 PM »
Can you attach your xml and I will take a look and see if there is an issue in it.
Hood
Re: G76 threading issues - any thougts?
« Reply #6 on: March 25, 2013, 05:24:43 PM »
Hood,

Sorry for the delay, external pressures pushing me away from playing with my toys!

XML attached for you to look through.

Further information:
Without going through the entire sequence, I have ended up hand coding a very simple G32 script - as below

G0 X2 Z22 (start point)
F50 (set feed rate)
G1 X0 (advance to the thread point at X=0)
G32 X0 Z0 F1.5 (Thread without changing X, to Z at 0 so 22 long and a pitch of 1.5mm)
G1 X2 (retract to X=2 at the end of the thread)
G0 X2 Z22 (return to start again)

I then copy/pasted a number of these into a file and inserted an M1 just before each G32.
Running the program lets the lathe cycle through over and over until some indeterminate point when the G32 results in a sound of steppers jumping, the DROs showing X at 0 and Z at about 0.5.
The program then stops several lines later, usually at the G1 X0 point and the program halts with the Run button flashing.

So completely mystified, the normal G0 and G1 cycles work perfectly happily and accurately but this entire threading cycle is driving me nuts!

Any thoughts gladly received.......

Simon

EDIT:
Forgot to say that I had a storage scope onto the index pulse and it is solid and clean...
« Last Edit: March 25, 2013, 05:42:59 PM by Simon0362 »

Offline Hood

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Re: G76 threading issues - any thougts?
« Reply #7 on: March 25, 2013, 07:06:08 PM »
Config menu, Ports and Pins, Spindle Setup, you have Use Feedback in Sync mode disabled.
Hood
Re: G76 threading issues - any thougts?
« Reply #8 on: March 26, 2013, 02:32:24 PM »
Sorry, wrong .xml - for some reason the 'current' one does not have the same name as the launcher. This one is *really* the current one, updated as of yesterday according to the file.

Simon

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Re: G76 threading issues - any thougts?
« Reply #9 on: March 26, 2013, 02:37:07 PM »
You have an Index Debounce of 100, I suspect that wont be helping, try it at 0.
Hood