Hello Guest it is September 19, 2019, 12:03:55 PM

Author Topic: G76 Lathe Theading Problem  (Read 12431 times)

0 Members and 1 Guest are viewing this topic.

G76 Lathe Theading Problem
« on: December 02, 2014, 12:44:22 PM »
Guys, I'm having a strange problem with threading on my lathe with Mach3.  I've not tried threading on this machine before so please keep that in mind.

It seems to execute the G76 command ok, but no matter what I put in for an X value it tries to run into the negative X.  The machine hits a soft limit a -0.100in and forces the tool back to 0.000.  It then just goes into an infinite loop.  Any ideas?

Also, this is a slant style lathe so the tool is on the back side and the spindle rotates CW.  I'm having trouble getting the tool to move in the -Z direction which is what I need to make a RH thread.  I start out at Z0.7 and the G76 line has Z1.0 but that doesn't work.  Seems like the G76 is trying to work but not correctly.

Sorry for not being more specific, I'm just not sure what to do!  Thanks guys!

Offline RICH

*
  • *
  •  7,361 7,361
    • View Profile
Re: G76 Lathe Theading Problem
« Reply #1 on: December 03, 2014, 09:30:30 AM »
What version of Mach are you using?
Post your xml file that you are using?
Post you gcode file.

RICH

Re: G76 Lathe Theading Problem
« Reply #2 on: December 04, 2014, 06:00:58 AM »
I meant to add that:

Version R3.043.066

G Code Test File:
-----------------
%
G30 U0. W0.
G90 G95 G54 G48 S2000
T0707
G97 S2500 M04


G00 X1.75 Z0.7

G01 X1.72 F.005

G76 P020560 Q10 R0.0050
G76 X1.72 Z1.0 P500 Q100 R0 F0.0556


G30 U0. W0.
M30

%
---------------------

You can put anything in for the X positions and it acts the same way.  I'm actually trying to make a much smaller thread (M22x1.0) but when that didn't work the first thing I tried was increasing the X's by a large amount, no change.

I can post the xml file too if you need.  Thanks!!!

Offline Hood

*
  •  25,849 25,849
  • Carnoustie, Scotland
    • View Profile
Re: G76 Lathe Theading Problem
« Reply #3 on: December 04, 2014, 07:15:59 AM »
Mach uses single line G76, have a look at the code produced by the simple threading wizard or have a look at the lathe manual to see what the code should be like.
Hood
Re: G76 Lathe Theading Problem
« Reply #4 on: December 04, 2014, 07:47:26 AM »
Interesting, I guess that I've never seen that explicitly stated.   Just a Mach3 thing, I assume?

Offline RICH

*
  • *
  •  7,361 7,361
    • View Profile
Re: G76 Lathe Theading Problem
« Reply #5 on: December 04, 2014, 08:00:41 AM »
There are different "dialects" of gcode so consult the Mach Manual as suggested.

RICH
Re: G76 Lathe Theading Problem
« Reply #6 on: December 04, 2014, 08:16:15 AM »
Any suggestions on how to re-write what I've been using?
Re: G76 Lathe Theading Problem
« Reply #7 on: December 04, 2014, 08:47:54 AM »
Run the threading wizard for a sample for code.

Also;
Some motion controllers work weird / wrong.
Sometimes the wizards work weird/wrong in threading. Its always consistent.

This is a very complex issue - and I am doing/will be doing a complete write-up on how to do *perfect threads* and howto.
It is affected by;
motion controller, mach3 version, imperial/metric, diameter/radius, and negatives/positives in some values in the wizard.
There are complex interactions in m3 and the wizards, and sometimes the problems show up and sometimes not.

The issues may appear for example when doing an inside vs outside thread, and or if the pullout angle is positive/negative (dont remember any more. I looked at this about 2 years back).
Just wanted to mention this, so You have an understanding why your combo may not appear to work vs other people.

I WILL have a working version in Mach4 with:
-With the motion controllers I use (CSMIO IPS, Pokeys) and metric. Other motion controllers as I get some.
-I will also document the imperial version
-Encoder threading or encoder index pulses
-Step/dir spindle (servo spindle or c-axis)


Re: G76 Lathe Theading Problem
« Reply #8 on: December 04, 2014, 03:07:14 PM »
hi
this is the way i write my code for threading on my denford orac cnc lathe , all my code is hand written because i could not get on with wizards
i am using version 062 of mach 3 , with the parallel port

this is my code for a m12 x 1mm pitch external thread
G0 X40.00 Z40.00  (tool change position)
G0 G40 G18 G80 G50 G90 G95
M6 T0505  (external threading tool)  
M3 S550  (spindle speed
G0 X12.00 Z15.00 (threading start point
G76 X10.78 Z-8.90 Q1 P1.000 J0.080 L45 H0.250 I29 C0.250  (thread cycle )
hope this helps you
robert
« Last Edit: December 04, 2014, 03:09:29 PM by ministeam »

Offline RICH

*
  • *
  •  7,361 7,361
    • View Profile
Re: G76 Lathe Theading Problem
« Reply #9 on: December 04, 2014, 05:06:37 PM »
Quote
I am doing/will be doing a complete write-up on how to do *perfect threads* and howto
Should be interesting and look forward to it.

There is a write up in Member's Doc's  called Threading on the Lathe - Mach 3 Turn. Not sure how Mach4 will address
tool touch off  and other things for the lathe. Quess we'll just need to waite and read the manual for Mach4 Lathe.

RICH