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Author Topic: Z height problem  (Read 5059 times)

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Offline Bobo

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Z height problem
« on: February 05, 2008, 08:15:27 AM »
I have been experiencing a Z height error on my machine. After about 30 minutes into a program machining a block of nylon, the Z would correctly raise up to 0.000 at the completion of a path, the gcode is calling for another 1/8 inch deeper cut, the DROs read correctly but the tool is 1/2 too high, cutting only air. Everything is very tight on the Z axis. It's a pinned lead screw drive and the axis is never under load at the time of the error. You can hear and see that the tool never touches the work. I can restart the program at the point of error and it continues correctly for some time and then the same Z axis error will occur, but I just keep re-zeroing the Z and restarting the program and completed the part. The error has always occured on the -Z instruction.

I mostly use the machine for Plasma cutting with a Bob Campbell THC controller and have never had this issue while plasma cutting. The THC was on at the time but the THC button in Mach3 was inactive. I'm running a 2 1/4 hp Hitachi Router Spindle.

I have not updated Mach3 for over a year. I'm at work right now, not sure what revision I'm running.

Does this sound like it could be a controller problem?

Thanks in advance for any help.
« Last Edit: February 05, 2008, 01:44:53 PM by Bobo »
Re: Z height problem
« Reply #1 on: February 05, 2008, 12:46:48 PM »
It sounds to me more like the tool offset is being turned off and is still off when you go back into the prog. I'd look close to the code for your error !
CRUISER
  Don

Offline Bobo

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Re: Z height problem
« Reply #2 on: February 05, 2008, 01:38:48 PM »
My original code did have a line: N0050 G43 Z-.025 H00 but I removed it. Here's the code I used to cut the part. A quick search showed no more G43 or G49 codes.
Re: Z height problem
« Reply #3 on: February 05, 2008, 05:43:19 PM »
There are end point errors in your code ! I never got past line 7 which i believe is equal to no10 of your numbering. end point errors may be giving your puter a stroke !
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  Don

Offline Bobo

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Re: Z height problem
« Reply #4 on: February 06, 2008, 08:15:41 AM »
Please excuse my ignorance, I'm by no means a skilled CNCist. Can you elaborate on the end point errors? Mach3 gave me no errors from the code while cutting the part. As my original post stated with the exception of the few -Z depth issues the part came out fine. I have cut thousands of parts using Unigraphics CADCAM software to generate the gcode for machined and plasma cut parts. This is the first time I had any unexplainable issues.

Thanks for your help.
Re: Z height problem
« Reply #5 on: February 06, 2008, 09:52:37 AM »
I just renamed your file to a tap file and loaded it into mach 3 and it told me you had an error or mismatch between the end point of the previous line to that line number, it probably isn't much, But my mach setup won't go past it ! Good luck to you, you'll find it what ever it is giving you problems
CRUISER
  Don

Offline Bobo

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Re: Z height problem
« Reply #6 on: February 06, 2008, 10:18:41 AM »
I believe your running in IJ Absolute mode. I'm running in IJ incremental mode. I was able to get the errors you are experiencing when changing modes. Unfortunately that doesn't solve my problem. But thanks for your input.
Re: Z height problem
« Reply #7 on: February 06, 2008, 11:42:44 AM »
Hi Bobo.
I've noticed a lot of problems after a Z- are caused by the z axis itself.
Is your 2 1/4 hp Hitachi Router Spindle loads heavier than the plasma gear?
If you ran the file with the plasma back on and it still didn't work, I guess that would rule out mechanical problems.

Jim

Offline Bobo

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Re: Z height problem
« Reply #8 on: February 06, 2008, 12:14:24 PM »
Good question Jim. Router spindle is definitely a good 5 to 10 lbs heavier. But I'm working on a ball slide with a 270 oz/in motor driving a 3/8-16 lead screw and the errors are all when dropping the spindle under no load. I will try running the program again without the spindle in free air and see what happens though.

Thanks for your feedback.
« Last Edit: February 06, 2008, 01:18:31 PM by Bobo »
Re: Z height problem
« Reply #9 on: February 06, 2008, 05:18:57 PM »
Hi Bobo.
I take your point, now I have looked at your pics of your machine. That's nice.
If it was me though, I would give it a wizz round the same file, without the spindle, rather than with the spindle, but cutting air.
The changes you have made are: a different file; a different head; and you have switched of some thc etc.
I would check it isn't something to do with the head first.

Jim