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Author Topic: Mach3 turn threading problem with Z feedrate  (Read 531 times)

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Mach3 turn threading problem with Z feedrate
« 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

Offline RICH

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Re: Mach3 turn threading problem with Z feedrate
« Reply #1 on: February 04, 2020, 05:04:24 AM »
Christian,

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


RICH
Re: Mach3 turn threading problem with Z feedrate
« Reply #2 on: February 04, 2020, 05:21:15 AM »
I read it so many times :D
Re: Mach3 turn threading problem with Z feedrate
« Reply #3 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...:)
Re: Mach3 turn threading problem with Z feedrate
« Reply #4 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

Offline RICH

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Re: Mach3 turn threading problem with Z feedrate
« Reply #5 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
Re: Mach3 turn threading problem with Z feedrate
« Reply #6 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.

Offline Graham Waterworth

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Re: Mach3 turn threading problem with Z feedrate
« Reply #7 on: February 08, 2020, 07:35:48 PM »
Too much de-bounce can also be a problem.
Without engineers the world stops
Re: Mach3 turn threading problem with Z feedrate
« Reply #8 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

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
Re: Mach3 turn threading problem with Z feedrate
« Reply #9 on: February 12, 2020, 09:28:38 AM »
The stepper drivers are 2M656.

Christian