Hole Spotting

I'm reasonably decent at CAD having used Fusion360 to design and 3D print for some time now.  However I'm a newbie (and I mean COMPLETE newbie) to CAM, gcode and post processors.  

I've built a 1500x1500mm downdraft plasma CNC table.  It's working rather well.  I've managed to get myself as far as the most basic of understanding manufacturing in Fusion.  Using the PP from the forum here I can get a flat pattern, generate a tool path and post it to an NC file and get parts cut with reasonable success.

I haven't figured out hole spotting though.  I know folks may say use something like Sheetcam and I'm sure it's a good solution but I'm trying to stay in Fusion (for now at least).

I tested QtPlasmaC's built in spotting function by writing a really simple gcode file to spot at the torch's current zeroed position and it works.  The built in spotting is quite nice actually.  Leaves a perfect little dimple (I'm testing with 1/8" aluminum sheet).  500ms pulse@20A

Before I try to reverse engineer the Fusion360 post processor to figure this out I'm wondering if there's any cool tricks in Fusion to get the PP to write the M3 $2 S1 command at a specific point.  

Or as a reasonable work around get it to write something out that's easy to search and replace with M3 $2 S1.   If that makes sense.

I did see something about adding in a drilling operation but when I tried it I discovered the free version of Fusion won't allow that.

Also not sure why the G91/G1microscopic move is necessary.  Pretty sure the tolerance settings will result in it being ignored but without it I get an error loading the file that it'll move outside my machine boundary.  I don't think that's the case but QtPlasmaC still throws the error.

Anyway I hope this isn't a bunch of utterly annoying newbie questions.    I sincerely appreciate any help with this part of the learning curve.

Cheers,

-Dave
 

Can't help in fusion but in Sheetcam you can create layers and you can define the minimum diameter of holes you can cut (say 12mm) so you move all of the small holes onto a new layer. When you generate the code for that layer  it will create the spots at the hole centre.
The torch won't fire if there is no movement in the following segment so move to relative coordinates to move a tiny amount to keep LinuxCNC happy and make the torch fire.

So now see if you can translate that to fusion.

dlv wrote:

I'm trying to stay in Fusion (for now at least).
 

In my opinion using Fusion for plasma (or laser) is like bought truck for drive to church - more troubles than benefits.
My favorite option is Librecad plus dxf2gcode - GPL and cost free.
Try this, even if you will not like them, this is simple and you will easy learn something.

Actually one way to do this would be to write a gcode filter for linuxCNC  that looked for hole below a certain diameter, removed the hole processing and replace it with a spot at the hole centre. Monokrom plasma has a filter that modifies hole processing so perhaps it can help you.

Another really out there possible solution that does not need post processing (but requires master branch) could  be to write a component or modify plasmac.comp and monitor the pin motion.interp.iscircle. When it goes true and motion.interp.arc-radius < minimum hole radius, disable the torch, use external offsets to move a distance of motion.interp.arc-radius along motion.interp.normal-heading (which will be your hole centre), fire the torch to spot, then unwind the offsets to return to where the torch was, let motion take over again then enable the torch when iscircle goes false.(the end of the hole)