Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: christian.avonto on February 04, 2020, 04:02:57 AM

Title: Mach3 turn threading problem with Z feedrate
Post by: christian.avonto on February 04, 2020, 04:02:57 AM
Hello everyone, I have a CNC converted lathe, everithing running fine with Mach3 turn from a few moths.
I need to thread now, and I have a problem, I can not understand why the Z axis movement starts with a different feedrate, and then stabilizes at the correct feedrate after a few millimeters. Everithing else is correct, if I change the RPM, the feedrate changes accordingly, but I can't figure out why at the start is different...
I attach a link to a little video of the problem. In this video I slow down the feedrate to make it easy to you to see what is the problem. You can hear the motor changing 2 times feedrate before going to the correct one.
It is the same with G76 or G32. I also tried to make some G1 passes in G95, and the feedrate is correct, but not in G32 or G76.
I think I have tried changing every settings in Mach3 with no luck. I hope there is something here that can help me.
Thank you very much.

https://drive.google.com/open?id=1_NKYLJ-pcKyUJI7g80QR5-i9lU1dOFSB (https://drive.google.com/open?id=1_NKYLJ-pcKyUJI7g80QR5-i9lU1dOFSB)
Title: Re: Mach3 turn threading problem with Z feedrate
Post by: RICH on February 04, 2020, 05:04:24 AM
Christian,

I suggest you have a read of "Threading On The Lathe - Mach3 Turn".


RICH
Title: Re: Mach3 turn threading problem with Z feedrate
Post by: christian.avonto on February 04, 2020, 05:21:15 AM
I read it so many times :D
Title: Re: Mach3 turn threading problem with Z feedrate
Post by: christian.avonto on February 04, 2020, 01:13:51 PM
Update: after an entire day of trying to change every setting, with no luck, today, after some normal turning, I tried again and it worked perfectly.
Don't ask me how...I don't know!
Only thing I've done I think is reinstalling Mach3 latest version after trying an older version with no luck.
I'll see tomorrow if it's still working ok...:)
Title: Re: Mach3 turn threading problem with Z feedrate
Post by: christian.avonto on February 06, 2020, 04:57:40 AM
Ok so, yesterday I tried several times, with no luck.
I have the spindle rotating at 100RPM, a pitch of 28mm, the first 15-20mm the Z axis starts at 30mm/rev, then goes to 32mm/rev for another 15-20mm and then goes to the correct 28mm/rev. I tried changing value of acceleration of the Z axis but in my opinion is not related, it does not change anything. The feed has to be 28mm/rev from the beginning, apart from the acceleration of the motor.
If anyone knows a possible solution to this (not only to start several millimeters away from the workpiece, I know it) I will appreciate it.
Thank you
Christian
Title: Re: Mach3 turn threading problem with Z feedrate
Post by: RICH on February 06, 2020, 09:01:12 AM
Christian,

Post your xml file  that you are using for the lathe. Just make a copy of the xml and rename it to something like
CHRIS RICH.XML and post it.

I see you are using  a modified screen set. Did you create or modifiy the standard 1024.lset?
Where did that screen set come from?

Run the "DriverTest.exe" file. How close is the Pulses per second in the test as compared to configured
Kernal Speed you selected in Port & Pins? (ie; test  shows 23506 as compared to 25000 HZ)
How clean is the graphics screen? Play with you mouse when you run the test, see what happens!..... that's why you should not play with the mouse when running  as you did in the video.

What version of Mach are you using?  Use Version R3.043.062

Use the Simple Threading (lathe) Wizard to generate the threading gcode. Fill in the required data, click Post Code, Click calc number of passes then you will see if you are exceeding  max feed rate.
( I would suggest that the code output be in G32 as it gives you info on each pass in case someting is wrong)

------------------------------------------------------------------
Some additional questions:

What are you using to acquire the index signal?

How steady is your RPM for whatever you set it at?
 Just for info you could check your rpm with a tack,but,let me say that Mach's rpm dro is more accurate than any tack you may have.

What drives are you using? If it's one of those chimes drive TB*********x ........ your on your owne as I can't help you!

more after you reply,

RICH
Title: Re: Mach3 turn threading problem with Z feedrate
Post by: natefoerg on February 08, 2020, 09:15:32 AM
Try programing the thread start further away from the work. Also, you might look at your spindle tach and make sure its got enough slot to get a good solid pulse from the tach sensor back to mach.

also, check motor acceleration settings and see if lowering them helps.

Also, my experience is with a slot too small on the tachometer disc, i could not get threading to work. Opened up the slot and it works fine for me. I do not think the mach rpom dro reads as accurate as you might think it does. I suspect this dro causes problems as it does not always appear to be tracking exactly the rpm.

These are just best guesses. based on past expierence.

Title: Re: Mach3 turn threading problem with Z feedrate
Post by: Graham Waterworth on February 08, 2020, 07:35:48 PM
Too much de-bounce can also be a problem.
Title: Re: Mach3 turn threading problem with Z feedrate
Post by: christian.avonto on February 12, 2020, 02:52:55 AM
Thank you all for your reply.

I attach here the xml.

I'm using a modified screenset from Franco CNC on youtube:

https://youtu.be/0R2JI__YhF4 (https://youtu.be/0R2JI__YhF4)

I ran the drivertest.exe program, and the result is very good, 25065 pulses, I attach a screenshot. Moving the mouse is ok, nothing strange happens.

The version I'm using is R3.043.062

I tried the threading wizard, in G76 and also in G32, and I tried also with a CAM postprocessor, the gcode is also in G32, but nothing changes, the problem is the same.

The stepper drivers aren't the TB6600, at this moment I don't remember exactly the model, but they are the standard black chinese drivers for Nema 34, I think DM856 or similar, I will confirm tomorrow.

Thank you for your time.

Christian
Title: Re: Mach3 turn threading problem with Z feedrate
Post by: christian.avonto on February 12, 2020, 09:28:38 AM
The stepper drivers are 2M656.

Christian
Title: Re: Mach3 turn threading problem with Z feedrate
Post by: Graham Waterworth on February 12, 2020, 06:14:46 PM
What size of thread are you trying to produce and can you post up the code you are using to do it.
Title: Re: Mach3 turn threading problem with Z feedrate
Post by: christian.avonto on February 13, 2020, 07:45:06 AM
It's the same whatever size I use, in G76 or G32.
In this particular case I was trying to do a 28mm pitch round profile thread in a piece of plastic.
Title: Re: Mach3 turn threading problem with Z feedrate
Post by: RICH on February 13, 2020, 07:51:18 AM
Christian,
- Are you using current reduction on the drives?
  1. I would suggest that you make sure that the current setting is correct for the steppers that you are using.
  2. Set drive SW4 to ON.
  3. Test axis  motion with steps per resolution seting of 2000 .(ie; need to set SW5,6,7,8)

Mach configuration:
  1. Tune the the steppers for velocity and acceleration and make sure the steps per unit are correct.
  2. Notice you are using Backlash for the Z axis. That SUCKS for threading! Test the axis motion with it
      off. ( .15 mm = .006" backlash )
      You have no backlash in the x axis?
  3. Can you set your set the spindle speed manualy?
      Mach3 and spindle control may be "fighting each other" for control of the feedrate during thread   
      cycle.

RICH
Title: Re: Mach3 turn threading problem with Z feedrate
Post by: christian.avonto on February 13, 2020, 08:32:33 AM
Rich, I actually don't have any current reduction in the drives. The current settings are correct for my size motors.
SW4 is already ON.
I have now set the steps per revolution at 1000, why have to try at 2000?
I already have correct steps per unit settings, I use the lathe frequently with no issues.
I have the backlash enabled yes, and in the pdf Threading on the lathe it says that works fine...however, I already tested it without it and the result is the same. The X axis is ok for backlash on my lathe.
I can't set the speed manually, I only set it via Mach3.
Thank you,
Christian
Title: Re: Mach3 turn threading problem with Z feedrate
Post by: RICH on February 13, 2020, 10:49:31 AM
I have now set the steps per revolution at 1000, why have to try at 2000?

Using 2000 you would be micro stepping at 10x. Above 10x there is nothing to be gained.

I can't set the speed manually, I only set it via Mach3.

The threading PDF talks about what happens when both Mach3 threading and the spindle control are both
trying to influence feedrate in threading. Some folks have no problem but others do and I think that may be your problem.
Until you try threading with setting spindle speed manually you will never know for sure!

RICH


Title: Re: Mach3 turn threading problem with Z feedrate
Post by: JohnHaine on February 17, 2020, 03:20:59 PM
Why are you wanting to cut a pitch of 28mm?  Maybe that is well outside the design envelope of the wizard and it generates errors.  Has anyone ever tried to cut a 28mm pitch using Mach3?

What happens if you try a more normal thread pitch, like 1 or 2 mm?  That may help to sort out whether it's a configuration problem or a controller bug.  I can imagine that there could easily be a bug with such large pitches because it may never have been tested.  If there is a bug in M3 it ain't going to get fixed now!
Title: Re: Mach3 turn threading problem with Z feedrate
Post by: RICH on February 18, 2020, 10:42:52 AM
Christian,

How was the gcode that was used in the video created? Did you code it?
Watching the video I notice your actually clicking buttons to change something........doesn't make sense!
Why the G04 P100 dwell part of the code.........doesn't make sense!
Noticed that the spindle RPM in the video was stable ie; 170 to 171

Do the following:
- Create the threading gcode using the "Simple Threading ( Lathe ) wizard.
   The inputs should represent a common metric thread. ie; M8-1.00

NOTE: The m1076 macro should set for G32 ( that's the output code that "I" want to see)
           as shown on page 47 in the threading manual. If you fooled with that macro in any
           other way AND  or OR  using a modified one done by someone else, replace  with
           the original m1076.mis provided with the original turn screen!

- After completing the inputs required, click the ( Calc number of passes ) button to make
  sure your NOT exceeding your max feedrate.

- take a screen shot of the Wizard screen.

- Click the Post Code and run it.

Please post both the screen shot and the generated code when you reply.

RICH


Title: Re: Mach3 turn threading problem with Z feedrate
Post by: christian.avonto on February 18, 2020, 03:12:41 PM
Rich, I was clicking to slow down the feedrate to see what's happening, without clicking it's the same, just don't consider that.

The G04 P100 dwell is there because I put it there, because between every change of direction the motor stalls, don't ask me why, because in normal turning also in G0 rapid doesn't stalls. Maybe it's for the accelerations, but they are the same with a little stop before moving, and with that doesn't stall anymore...I think is for the too fast change in direction.

If I create a standard threading code with the wizard, like M8x1.0, I think I can't see the problem, if it's there, because in proportion the movement is a lot smaller...but I will try.

The macro is the original one, I tried with G76 and with G32 from that macro.

I will try your suggestions as soon as I have some time, now I'm really busy and can't try them.

Thank you for your time for now.

Christian