I know the goto zero function does exactly that, but I zero my z-axis to the table when cutting with a drag knife.  The last place I want the tool is sitting on the table.  Is it possible to alter the goto zero function such that it moves the x and y axis to zero and leaves the z axis at the safe z-height?

Hi SM,

Welcome to the forum.

Is it possible to alter the goto zero function such that it moves the x and y axis to zero and leaves the z axis at the safe z-height?

(Depending on your screen set) - The existing Goto Zero button executes an OEM code but if you are prepared to use a screen designer such as "Klaus's Mach Screen" there is nothing to stop you replacing the Goto Zero button with an identical looking VB button which contains the code of your choice - for example moving the Z axis to a safe height then zero the X and Y axes.

It is bit of a learning curve but worth the effort.

http://www.machsupport.com/software/downloads-updates/screensets/
http://www.machsupport.com/help-learning/videos-tutorials/

Tweakie.

You could edit the screenset so that that button is a G Code or a VB button. If you make it a G Code button then you enter the G Code you wish from within the screen editor, if a VB button then you do from within Mach.
The difference is a VB button can have more than one line of code where a G Code button can only have one.
In this case the G Code would suffice however, so up to you which way you do it.
Hood

I appreciate the input guys.  By about midnight, this was sort of my conclusion.  I've started with modifying an existing screen.

Perhaps you can answer one other question which I should probably put elsewhere, but I'll give it a try here.  Would it be possible to embed our drag knife swivel code in the mach3 operation, such that the swivel actions are added on the fly as the g-code is executing.  Basically this swivel code finds a corner in a g-code program and makes modifications such that the knife is lifted, turned, and then lowered back to the cutting depth.

Take a look here: http://donektools.com/free-cnc-router-software/links-2/

Would it be possible to embed our drag knife swivel code in the mach3 operation, such that the swivel actions are added on the fly as the g-code is executing.  Basically this swivel code finds a corner in a g-code program and makes modifications such that the knife is lifted, turned, and then lowered back to the cutting depth.

The Mach3 "Tangential control" does the job - although there are some special rules to be observed with arc circles, it is simple enough to use.

Tweakie.

is there a tutorial on that somewhere?  I'm not talking about a typical tangential knife controlled by a motor.  This is a drag knife that works like a castor.  If chucks into a router collet and is completely passive.  Orientations are controled by the X & Y axis.  See this:
http://youtu.be/63u9idcyVhA?t=7m55s

OK, I understand now what you are referring to.
No, Mach3 does not do that unless the tool-path has been created with a sign making software as this is basically a job for the CAD /CAM software rather than Mach3.
I may be wrong but I believe that Aspire4 now incorporates this feature in it's gadgets. 

Tweakie.

Yes.  I am the owner of Donek Tools.  I worked with Vectric to create that gadget.  Sheetcam also has similar capabilities.

The next step would be to make it unnecessary to add those actions to the toolpath and actually have the control software do it.  Then the tool could be treated like any engraving tool when generating tool paths.  The calculations are not that complex and should be well within the processing power of the control software.  The question is, is it possible, as a user, to add this type of functionality or customization to Mach3?

It could be done at the load g-code step, such that as the code is imported, it is processed, or it could be done at the run g-code side, such that the file is altered as it is sent to the machine.