2-Axis CNC Mill- Creating X Y only tool-path that does not cut into part

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Rauch_Schall
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Joined: Fri Jul 31, 2020 11:07 am

2-Axis CNC Mill- Creating X Y only tool-path that does not cut into part

Postby Rauch_Schall » Fri Jul 31, 2020 11:25 am

Hi all,
For my self-made CNC Mill (only X and Y axis are automated, Z is manual) I am trying to generate a path from an array of parts.
These parts are meant to be milled from sheet metal, and ideally, FreeCAD would generate a path where the parts profiles are milled out one-by-one, milling through the stock to get the tool from one part to the next.

A sane person that has a 3-Axis Mill wont have any problem with the generated paths because they can just use rapid operations to get out of the stock material, and jump over to the next parts tool path.

By being limited to 2-Axes only, i however have the issue that my tool never gets to a safe height to do those rapid moves, resulting in it cutting through my parts to get to the next one in line. Now i wonder if there is a straight forward way of generating a path that never cuts into my parts but only moves in the space between them, only using X and Y axes.

Would e.g. a sketch work where i draw in the moves between parts by hand, and then use an edge-profiling job for the path generation?
GeneFC
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Location: Punta Gorda, FL

Re: 2-Axis CNC Mill- Creating X Y only tool-path that does not cut into part

Postby GeneFC » Fri Jul 31, 2020 2:07 pm

One way to handle this problem would be to add pause operations at the end of each pattern. Probably an M0 or M1, although you did not say what controller you are using. You would need to add another pause at the end of the x-y repositioning before lowering the z-axis to cutting height.

I don't see any way that FreeCAD can know when you have manually raised the z-axis to a safe height. There is no feedback from the cutting machine back to FreeCAD.

Gene
Rauch_Schall
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Joined: Fri Jul 31, 2020 11:07 am

Re: 2-Axis CNC Mill- Creating X Y only tool-path that does not cut into part

Postby Rauch_Schall » Fri Jul 31, 2020 3:21 pm

Thats a smart suggestion and in the long-run i will definetely adopt it! With the particular problem at hand though, i was hoping to keep the endmill in the stock for the entire path and just mill my way from one part to another without pulling out. This would require the path planning to avoid my parts and use the space in between to get to the next one - this would greatly speed up things, but is where i am stuck :)

I am using GRBL together with bCNC
RatonLaveur
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Re: 2-Axis CNC Mill- Creating X Y only tool-path that does not cut into part

Postby RatonLaveur » Fri Jul 31, 2020 8:52 pm

Then that's super easy: change your postprocessor to remove all Z arguments.
GeneFC
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Location: Punta Gorda, FL

Re: 2-Axis CNC Mill- Creating X Y only tool-path that does not cut into part

Postby GeneFC » Sat Aug 01, 2020 12:25 am

RatonLaveur wrote:
Fri Jul 31, 2020 8:52 pm
change your postprocessor to remove all Z arguments.
That would actually be remarkably ineffective, since his machine totally ignores z commands in any case. :lol:

The problem is a bit different than I first understood. There is no way in the Path WB to specifically direct the rapid motion between arrayed objects. It may be possible to create an actual cutting path to replace the rapids, but I suspect that would take a lot of work with custom g-code. One can create "start points", but I don't think there is any way to create an "end point." The process of building the custom rapid-replacement needs to know the end point of the profile operation. Every design, even with rather small changes, might be quite different.

It might also be possible to create some dummy structures to make sure the "between" path did not blindly plow through the desired objects already processed or yet to be processed. Again, the difficulty is that there is no user control of the rapid path. I do not know if the avoidance strategy would be robust and trusted.

Gene
herbk
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Re: 2-Axis CNC Mill- Creating X Y only tool-path that does not cut into part

Postby herbk » Sat Aug 01, 2020 7:49 am

Hi Gene,
GeneFC wrote:
Sat Aug 01, 2020 12:25 am
One can create "start points", but I don't think there is any way to create an "end point."
because the OPs are closed loops, start- and endpoint of an OP is the same, - ore am i wrong here?

To the problem itself:
It's an self builded machine... In my mind the best and most comfortable way to solve the prob would be: add an automated Z axis to. ;) :lol: :lol:
Gruß Herbert
chrisb
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Re: 2-Axis CNC Mill- Creating X Y only tool-path that does not cut into part

Postby chrisb » Sat Aug 01, 2020 10:48 am

RatonLaveur wrote:
Fri Jul 31, 2020 8:52 pm
Then that's super easy: change your postprocessor to remove all Z arguments.
Not remove, as Gene suggested, replace them with a wait command.
spanner888
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Joined: Tue May 28, 2019 10:51 am

Re: 2-Axis CNC Mill- Creating X Y only tool-path that does not cut into part

Postby spanner888 » Sat Aug 01, 2020 10:54 am

As you are using bCNC, you can easily find the end of the gcode of each part and insert a new gcode block and add gcode command(s) to move to your desired next location. Yes this is manual, a a little bit of work, but better than cutting through your parts.

I f you have not looked, read the bCNC wiki about the gcode editor capabilty, you can select gcode by clicking on the GUI view of the paths etc.
GeneFC
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Re: 2-Axis CNC Mill- Creating X Y only tool-path that does not cut into part

Postby GeneFC » Sat Aug 01, 2020 2:44 pm

herbk wrote:
Sat Aug 01, 2020 7:49 am
because the OPs are closed loops, start- and endpoint of an OP is the same, - ore am i wrong here?
We do not have enough information to know.

I guessed that the OP wanted to set up a repeatable system to do this sort of operation on a number of designs. If it is only for a "one-off", then anything will work. If it is for arbitrary shapes, then it will be hard to find an automatic method that does not require a lot of hand path coding.

Gene