How to make Z axis code always in negative direction.

[Anonymous]

First post here.  I am very new to 3D modeling, but not new to Autocad and am trying to teach myself Fusion 360.  It has been a very tough road so far. 

I am using Linux CNC software on a converted Bridgeport vertical mill.  The Z-axis within EMC is configured that Z- zero is with the spindle fully retracted.  So, any "Z" move will be in the negative direction.  My problem is that whenever I generate G-code for my parts, there are a large number of Positive "Z" axis moves injected into the code, which makes my machine error out with "Z move will exceed positive limit" for that axis. 

Is there some way to "offset" the Z so that the post processor knows that the top surface of the part will always start at Z=-.500?  Thanks!

[Laurens-3DTechDraw]

You know you can set a work offset in the machine?

You don't have to work from machine zero.

[Anonymous]

What work offset, specifically are you recommending?  After I start the machine and home all axes, I run the Z down to Z -1.00 and then "touch off" to make that position zero.  When I try to run the program, I still get "Linear move on line 14 would exceed joint 2's positive limit."  I am a hobbiest transitioning from an environment where most of my prior G-code programs were hand written, so this is a pretty big jump for me.  My G-code is attached, below.

[Anonymous]

Any chance that anyone else has an answer to my question in post #3 of this thread?  If not, is there a more active forum somewhere else for Fusion 360 where I should be asking questions?   I am sure that I am not the only one to have had to overcome this same obstacle.  Thanks!

[jeff.walters]

If your machine doesn’t have work offsets and will ONLY run from machine home (I used to run one) then you should set your WCS the where your machine home will be relative to the part. You can put a point at that place and then select it for the location of the WCS in the Setup.  

[Anonymous]

Yes, I had thought about doing a "construction line" in the "Model" space of the drawing, to create a line that ended at Z +.500 above the part, and then drag the 3D axis indicator up to the end of that line.  I didn't know if that was the right solution to use.  Also, I am not familiar with using Work offsets in G-code, so I have that working against me on the machine side. 

Aside from re-zeroing my machine with the Z axis down one inch, is there something else I should be doing on the EMC (LinuxCNC) side to properly handle this offset?  Thanks!

[Laurens-3DTechDraw]

Here a page on workoffsets in linuxCNC: http://linuxcnc.org/docs/html/gcode/coordinates.html

Here is a basic CNC 101± http://forums.autodesk.com/t5/computer-aided-machining-cam/cnc-101/td-p/5902421

[Anonymous]

Thanks for the links to the good resources.  Have not had a chance to watch all the videos yet, but have done some reading on Offsets.  Still trying to figure out if just doing a "touch off" in the Linux CNC software to shift the position of the axes will be sufficient to let me compensate for the actual origin of the G-code generated from the Fusion CAM output.  Thanks!