How do I touch off during a tool change?

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04 Nov 2010 21:54 #5087 by gridley
Hello,

I am using BobCad to generate my G-code. BobCad will not drill a hole without a center drill step. When it prompts me to change the tool from the center drill to the drill bit, I need to touch off the Z axis because the tools are different lengths. Axis won't allow me to touch off while the program is running.

Any suggestions?

Thanks for the help,

Gridley

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04 Nov 2010 22:34 #5090 by andypugh
It's a much-requested feature. :-(

If you can set up the tools with the correct tools in the tool table, then it should all work. If you are using collets or chucks then collars round the tools might be an option.

(Better might be to edit the centre-drill section of the G-code out)

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04 Nov 2010 22:49 #5092 by BigJohnT
gridley wrote:

Hello,

I am using BobCad to generate my G-code.
Any suggestions?

Gridley


In addition to what Andy said my suggestion is to get rid of BobCr@p... Sorry, I had it once and it was the worst software I have ever tried to use and the high pressure sales force still calls me and e-mails me to this day.

I forget if you can modify the post processor or not to remove the center drill part but you might look.

John

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09 Nov 2010 16:51 #5177 by photomankc
So I understand, since I will have manual tool changes during a program, I can not touch off between one tool and the next while the program is running? I would have to make each step using a new tool into a separate program?

Has not effected me yet since my Z is not converted at this time so I already have to do it this way for most parts anyway. But I never stopped to consider that and I can see that being a problem down the line.

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09 Nov 2010 17:24 #5178 by andypugh
photomankc wrote:

So I understand, since I will have manual tool changes during a program, I can not touch off between one tool and the next while the program is running? I would have to make each step using a new tool into a separate program?


That is the simplest way round the issue, yes.

In some ways it is not as big a problem as it might seem, as if you are doing manual toolchanges then you have to stand at the machine anyway and breaking the program up into steps can make restarting after minor problems easier.

Any toolholding option that can allow repeatable tool-length (or repeatable-enough) will allow you to touch-off all tools before the start and then run through using tool-table offsets. I found my No-3 Morse spindle to be OK, R8 would be a lot better. INT, CAT or BT are specifically designed for the job, so I assume that is not what you have.
The problem comes if you are looking to change between cutters held in collets. In that case depth-stop rings pressed onto the tool might work, as would mounting the tools in solid collets. (Not that I know if you can buy solid collets, the idea only just occurred to me).

The reason for this is buried in the way that EMC2 works, and is explained in some detail here:
wiki.linuxcnc.org/cgi-bin/emcinfo.pl?WhyManualWhilePausedIsHard

Though that addresses a slightly different question. (Pause, change tool/clear swarf, resume)

There is an unsupported patch (that I can't currently find) that allows limited manual control during tool-change, but I think it introduced problems.

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10 Nov 2010 12:44 #5197 by Mike_Eitel
Very good explanaition from John Kasunich.

THX for that hint

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10 Nov 2010 13:04 #5198 by BigJohnT
John K. has some good reasons why tool touch off can not be done while the program is paused using the pause button, however I don't any reason why a M0, M1, or M60 could not be used to allow a manual tool change as the motion cue would be empty like a spindle speed change does. All that needs to be done is make the interpreter stop at a M0, M1, or M60 so everything is clean inside EMC. M60 is a pallet change and seems to me to be the likely candidate for a tool change too. But I think in simple ways usually.

Just my 2 cents.
John

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10 Nov 2010 13:07 - 10 Nov 2010 13:09 #5199 by andypugh
Reading it again in detail, I think it is almost certain that toolchange is a "queue buster", so many of the issues there do not exist.

I also have a feeling that it would be possible to add a tool-length probe to the toolchange sequence, so there would be no need to touch-off the tool.
Last edit: 10 Nov 2010 13:09 by andypugh.

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10 Nov 2010 20:07 - 10 Nov 2010 20:09 #5202 by andypugh
Attached is a version of hal_manualtoolchange that Les Newel modified to allow jogging during toolchange.

I have never used it, and I believe that it has certain undefined problems. If you put it in the same place as the other one, then using it should be a trivial change to the HAL file.

The file will need the spurious "txt" suffix removing and replacing with .py .

File Attachment:

File Name: hal_manual...nge1.txt
File Size:2 KB
Attachments:
Last edit: 10 Nov 2010 20:09 by andypugh.

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14 Nov 2010 17:14 #5301 by eslavko
I use that script without problems. But I expect problems if G code has some subroutines.

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