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Author Topic: Plasma - Handling misaligned materials - G68 does not work  (Read 4076 times)

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Plasma - Handling misaligned materials - G68 does not work
« on: February 20, 2012, 04:15:41 PM »
Hi everyone,
I would like to use G68 G-Code for a precise alignment of the materials to the X/Y axises on my plasma table  Along with G68, I also need to use 28.1 g-code which is required for IHS (Initial Height Sensing) routine in MP3000 post-processor.

The problem is that Mach3 tries to send X/Y axises to search for home switches right after the "G28.1 Z10" code is read by Mach3. This only happens while in G68 mode ("Local System Rotated" in MDI page has a value other than "0" zero) Other times G28.1 Z10 code does not cause this type of behavior and does not move X/Y axises. Is this a bug? Or is it something that I am doing wrong? 

Rotating coordinates with G68 is an essential feature for me as a Mach3 Plasma user. I deal with very large and heavy materials, some weighing more than a ton, and aligning them to the table's X/Y axises or going back and forth to Sheetcam to align the parts to the skewed material is really a big hassle.

I would appreciate your help. Thanks in advance...

Offline BR549

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Re: Plasma - Handling misaligned materials - G68 does not work
« Reply #1 on: February 20, 2012, 04:24:40 PM »
HIYA EFE, As you have found out MACH3 will NOT allow you to run the G28.1 while in a G68 rotated position. This is a MACH3 problem that really puts a kink in using the G68 for most plasma work. AND in this case the G68 is needed more here than in most other uses of MACH3.

THere IS a workaround.  Instead of using the G28.1 Zxx  (refhome Z ) You have to set your plasma up to USE the G31 function to find the TOM(top of Material) it ALSO has problems BUT will make the G68 useable for plasma cutting.

SO what you need to do is setup your floating head contact to be a probe instead of a home switch. Then use a different POST that calls the G31 instead of the G28.1. In  Sheetcam you would use the THC300 post instead of the MP1000 post.

Hopefully some day Mach3 will allow it to be done using the proper G28.1 call.

Hope that helps, (;-) TP

« Last Edit: February 20, 2012, 04:29:04 PM by BR549 »
Re: Plasma - Handling misaligned materials - G68 does not work
« Reply #2 on: February 20, 2012, 05:12:24 PM »
Thanks for the reply, TP. I appreciate very much. I agree. This is indeed an essential feature for plasma work. I am puzzled as to why Mach does not allow G28.1 when used in conjunction with G68. I am hoping someone can shed a light on this issue.
I will try the G31 workaround you mentioned. Hopefully it is not something that is out of my league as I am not good with dealing with post-processors. :(
Again, thanks for the help...

Offline BR549

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Re: Plasma - Handling misaligned materials - G68 does not work
« Reply #3 on: February 20, 2012, 05:20:04 PM »
EFE you won't have to modify teh POST just use the one for THC300.

Let me know IF you need more help with it.

(;-) TP
Re: Plasma - Handling misaligned materials - G68 does not work
« Reply #4 on: February 21, 2012, 07:19:48 PM »
Thanks TP...I'll certainly need your help with this setup. I"ll be back with more questions after I give it a try.
Re: Plasma - Handling misaligned materials - G68 does not work
« Reply #5 on: February 29, 2012, 07:52:06 PM »
TP, sorry for the delay in updating the status of the my post. I already tried your suggestion and it worked. I can't thank you enough.

I can now use G68 in Mach without having to deal with the trouble of aligning the material precisely to the table's axises. What a relief!

THC 300 post processor seemed to work fine as well without any major changes. All I have done was to add Z switch offset value to mach my floating head switch offset.

You mentioned that using G31 also has problems. What kind of problems should I anticipate?

Thanks in advance...

Offline BR549

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Re: Plasma - Handling misaligned materials - G68 does not work
« Reply #6 on: February 29, 2012, 08:11:39 PM »
In the way you are using it you should not have any problem .

(;-) TP