Hello Guest it is December 06, 2019, 02:41:15 AM

Author Topic: Z Axis will not go below about -1mm when running - but thinks its going deeper?  (Read 1492 times)

0 Members and 1 Guest are viewing this topic.

Hello.

Ive been having a problem with my diy built cnc router today and was wondering if anyone could help me?

It normally runs fine, and it cut the first panel fine this morning, i then re skimmed my vacuum bed and tried to cut the 2nd panel, the first operation is drill a load of screw holes but when i start the program the cutter stops just below the surface of the plywood, the DROs keep counting down to -15.5mm like it should then it retracts to what it now thinks is a safe z of +5 and gos too far and hits the limit switch.... So as it has not moved down when it should have done i have to re set the z zero to try again...

I have tried restarting mach 3 / the PC, resetting the driver boards etc and making new g code, (i have had this issue before about a year ago and this seemed to get rid of it, but today it just wont have it...) Sometimes by resetting i have managed to get it to drill 5-6 holes and then it just has the problem again... I dont think it is a mechanical issue with the machine, it was running for several hours yesterday with no issues, i know it will plunge cut fine at that speed, the issue seems to be with the control or the computer, or with mach 3.

The only thing i can think of that changed between cutting the first panel and the 2nd panel is i skimmed the bed, so when i came to set the zero point for the 2nd panel it was 1mm lower. I use work coordinates and dont really use the machine coordinates or soft limits, i rely on my limit switches, i increased the soft max and soft min anyway but it made no difference...

I really dont know what is causing this, like i said it does it pretty much all the time, sometimes it will drill a few holes then do it, i read in another thread about issues with the parallel port driver not driving the break out board with enough current, but i can jog about fine i have no issues going below -1mm...

I was thinking it could be an interference issue as its only happening when the spindle is running, but ive just tried running the program with the spindle and inverter switched off and it still has the same problem...


Can anyone help?

Many thanks

James

Offline Tweakie.CNC

*
  • *
  •  8,010 8,010
  • Super Kitty
    • View Profile
    • Tweakie.CNC
My thoughts are that Mach3 is running correctly and that your Z axis is stalling on the way down.
Try halving the Velocity and Acceleration settings in Motor Tuning for you Z axis (remembering to save the changes) and see if that makes any difference.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Thanks but im 99% sure its not stalling,  it jogs up and down absolutely fine every time,  and when it does eventually run its drills the screw holes fine, and it dosent make the sound that it makes when stalling. 

Cheers.

James

 

Offline ger21

*
  • *
  •  6,289 6,289
    • View Profile
    • The CNC Woodworker
Quote
the DROs keep counting down to -15.5mm like it should

This means that Mach3 is working correctly. You either have a motor stalling, or a mechanical issue.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Quote
the DROs keep counting down to -15.5mm like it should

This means that Mach3 is working correctly. You either have a motor stalling, or a mechanical issue.

But it does exactly the same thing when its running a program and not machining anything, just moving around in air it comes to about -0.5mm and stops,  It jogs up and down past the -0.5mm point fine every time, it only happens when running a program...

Ill try writing a basic program with some simple up down moves and see if it runs that, it might be something to do with the spiral down move..., But like i said i ran the exact same program from the exact same usb stick yesterday morning and it ran absolutely fine... then i did a bed skim as the first panel was not quite level,  then tried to run the program again and it just wont have it...

Offline ger21

*
  • *
  •  6,289 6,289
    • View Profile
    • The CNC Woodworker
Maybe a tool length offset then.
Do you have a G43 in your code, and a length value in your tool table for the tool called with G43?
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
No G43 or tool length specified, just T0 tool diameter.  Ill have a go with some basic up down programs tomorrow. 

Cheers.

James