[RJ02]

Hey I appreciate any help you guys could give me. I have a cnc router I bought as a kit and put together. I'm using Mach3 software. When I zero the Z axis on the top of the part surface, when I run the program, the Z axis moves up farther than it should. So it's only cutting air. If I re-zero it again, it usually does okay. Any thoughts on what could be wrong? Thanks in advance!

[RCaffin]

Several possibilities here. Loose tool in chuck, noise in step line to Z axis, backlash, etc etc. Proper testing needed.

Put a bit of round rod with a very square end in the spindle chuck (or whatever). Bring it down fairly low to engage a dial indicator and zero both the Z axis and the DI. Move up 5.00 mm and rezero the Z axis. Then cycle up and down by 50 mm for 20 cycles. Then take the X axis back to -5.00 mm. Does that bring the DI back to zero?

If it does, then maybe the tool was slipping in the chuck. If it does not, then the Z axis drive is getting noise and creeping.

Cheers
Roger

[RJ02]

Thanks for the quick response. I know it's not a loose tool in the chuck and don't believe it could be backlash. When it does this usually only on the first start up of a program, the Z will move up to the clear plane and then move another inch up. If it was noise on the line, why would that be the only times that it does this? I can run your check suggestion first chance I get. Thanks again!

[RCaffin]

usually only on the first start up of a program, the Z will move up to the clear plane and then move another inch up.

Wierd!

* OK, what machine, what sort of motors, what sort of drivers, what sort of ontroller and what sort of BoBs, and what PC SW (Mach?)?

* When this happens, does the Z axis readout on the screen show movement for the extra inch?

Cheers
Roger

[ger21]

Most likely, your trying to move it faster than the motors are capable of, and it's losing position. Reduce your acceleration and velocity by half, and see if it's better.

[RJ02]

Machine is a kit from cncconversionkit.com. Motors are nema 23, 425 oz. in. drivers are DM556D, C10 BoB, Windows XP, Mach3, 2.0. When this happens, whatever the Z dro is reading, I think 1.00, if I tell it to got to zero, it moves down, but is off the work surface about the amount of the clearance plane and dro reads zero. Thanks!

[RJ02]

I've already got the Z axis acceleration about half of what the X and Y are. If that was the reason, it still doesn't make sense why on the second zeroing of the Z axis, it usually will work fine. Thank you.

[RCaffin]

I don't understand the 'clearance plane' bit. Do you mean the 'Z safe' limit?
If it all works fine after the second zeroing, a bit odd.

Anyhow, what happens with the cycle test?

Cheers
Roger

[ger21]

What are your Z accel and velocity settings?
Does your Z axis have a 5mm pitch ballscrew?

[RJ02]

Okay, the Z accel is 2 in/sec, and velocity is 50 in/min. Ballscrew is 5mm pitch. I tried reducing both the accel and velocity to v = 25 in/min and accel = .75 in/sec, and it still did the same thing. Only on the first time, after second zeroing, it's just fine.
The clearplane is what Dolphin Cam calls clearance of all obstructions, you set it to whatever you want. I usually use .25"
I did test it again and the difference is 1" when it messes up. I zero it after its gone too far and it is 1" above work. It is odd that this happens.

[RJ02]

Oh, I forgot to mention, I haven't had a chance to do the cycle test yet.

[ger21]

Where did you get Mach3 2.0, and why are you using such an old version?

You should be able to use an accel of 5-10 or so. Is there any binding in the screw?

What is your procedure for zeroing? If it works OK after zeroing a second time, can you just zero twice and it'll always work??
Explain exactly what you're doing, because this makes no sense at all, and would point to a Mach3 issue. If you really have a 2.0 version, update to the latest version and see if it still does it.

[RJ02]

I got the mach3 from their website in Nov. 2012. How do I update it?
Doesn't appear to be any binding in the screw.
Zeroing method is, manually move Z down to work surface and use a sheet of paper between work surface and cutter, and get it to where I can just slide the paper out. Then I zero the DRO.
I've actually tried several different auto zero scripts, and they all work at first and then they end up doing similar to this problem, they move up too far after zeroing.
I could just zero twice every time, but I have to start the program and then stop it and rewind it, re-zero. It's just a pain in the butt. Thanks!

[ger21]

Go to Machsupport.com and download and install the latest version.

[RCaffin]

Have to agree with Gerry there. V2 ... who knows what bugs?

But we still do NOT know whether the DRO shows that extra movement or not. Two totally different cases. Without that knowledge we are stuck.

Cheers
Roger

[RJ02]

I've downloaded the latest version of Mach3, 3.043.066. I'll install on the computer that runs the cnc tomorrow night. It's not connected to the internet.
I did discover that I had version 3.043.022. I thought I had 2.0, 'cause that's what shows on the logo when mach3 loads up. I hope this will solve the problem. Thanks a bunch! I'll let you know what happens.

[RJ02]

The DRO does not show the extra movement.. When it does this, the cutter is touching the work surface, I click start program, cutter should move up .25" and start to go wherever. But instead, it goes up 1.25" and DRO says 1", so when it comes down to where zero should be, it's 1" off the work surface.

[RCaffin]

Hi RJ

My advice is do NOT load .066. That version has some real bugs! Lots of users will tell you that.
.022 works fine - I am using it a lot.
.062 is OK as well, possibly better than .066. If you want to update, use .062

Cheers
Roger


Ah - that 'V2' logo. Yeah, never updated.

Cheers
Roger

[RCaffin]

cutter should move up .25" and start to go wherever. But instead, it goes up 1.25" and DRO says 1", so when it comes down to where zero should be, it's 1" off the work surface.

Ah - that does not make sense.
Do you mean it should go up 0.25" but goes up 1.25" and the DRO shows 0.25"?
If my version is correct, then we are getting somewhere.

Cheers
Roger

[RJ02]

Yes, that is correct. I may have stated it wrong earlier, I said DRO showed 1, but it does show .25 but went up 1.25. I just went downstairs and checked it. It appears that it does this upon starting mach3 and loading the program. I closed mach and reloaded several times and that's when it seems to do this.