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General Mach Discussion / Re: First post: Mach3 machine and workspace offsets, auto home, and auto tool offset

« on: July 29, 2017, 08:46:27 AM »

Thanks, Rich. I'll look for the Peter Smid book. I think I started out following exactly your suggested route. I find machine zero (Ref All Home in Mach3).

I have fixture plates, each with multiple stations that are fixed relative to the plate.

I used G54, G55 etc. to specify the locations of each fixture relative to the plate. That didn't work, since each local workspace has to be defined by offsets from machine coordinates. Not a big problem - I know where the plate is in machine coordinates, so I can translate. I define G54 etc. relative to machine coordinates. So far, so good.

Now, I measure Z offset for a tool. That applies ONLY to the current coordinate system - G54, for example. Works great on the first fixture, but not so much when I switch to G55 for the next fixture.

An added wrinkle is that currently, my machine zero to plate offset isn't as repeatable as I'd like. I've considered probing the plate and setting machine coordinates based on the current plate. Cheating, I know, but I think it would work in this situation and eliminate one source of errors.
Clearly I need to do a bit more reading. Thanks again for the pointers.

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General Mach Discussion / Re: First post: Mach3 machine and workspace offsets, auto home, and auto tool offset

« on: July 28, 2017, 08:58:09 AM »

How are you generating your g-code?

I'm creating 2D drawings with Draftsight. I use 'dxf2gcode' to generate the initial gcode. I then manually edit to fine-tune the results as needed.

I pass the initial Draftsight DXF through a simple homebrew post-processor that modifies the layer names to match what dxf2gcode wants to see - it is smart about how to handle a layer named 'DRILL:' for instance, and Draftsight doesn't allow special characters like ':' in layer names.

3

General Mach Discussion / Re: First post: Mach3 machine and workspace offsets, auto home, and auto tool offset

« on: July 27, 2017, 07:54:56 AM »

Thanks. Based on a fair amount of reading and research, I was using a different individual workspace (G54, G55, etc.)for each fixture on the plate.

After reading this and thinking a bit more, it seems like it might make more sense to leave machine coordinates alone, use X-Y-Z tool offsets to establish the fixture plate location in the G54 workspace, and then use G52 offsets for each fixture on the plate. I'll try that today.

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General Mach Discussion / Re: First post: Mach3 machine and workspace offsets, auto home, and auto tool offset

« on: July 26, 2017, 08:46:29 PM »

Thanks. I'm also experimenting with G52 offset, which seems to apply to all workspaces. I set the G52 Z offset to zero, touch the target, then set a new G52 offset based on the reading. I *think* it works, but I need to test it more thoroughly.

What is G52 usually used for?

5

General Mach Discussion / First post: Mach3 machine and workspace offsets, auto home, and auto tool offset

« on: July 26, 2017, 02:30:33 PM »

I have a small CNC mill and I'm stuck trying to navigate the whole offset thing. Here's what I'm trying to do:

I have a number of fixture plates, each set up to hold multiple copies of a particular part so that I can make five left handed skyhook brackets at a time, for instance. Only one fixture plate fits on the machine at one time.
Each plate has an x-y-z target that I can probe to locate the plate.

I'd like to locate the plate, and on each tool change, set Z offset relative to the plate.

My original approach was to auto-home the mill using the target on the current plate, so the machine coordinates match the plate coordinates. That works fine.

In the part program, I define a workspace coordinate system (G54, G55, etc.) for each part station on the plate. That also works fine.

However, when I change a tool and determine the new Z offset, that only applies to the current workspace. I can make a proper part in one workspace, but not in any of the others.

Is there a way to do Z axis tool offset and have it apply to all workspaces? Is there a better way of thinking about this?

Thanks for any help or insights.