Z Height CAM Code is wrong; Too deep

[invetech54915]

I am having an issue with Z height that I have never experienced before and can't figure out why it is happening.  I am using Fusion 360 and Mach 3.  I have a 19mm work piece that I have a 3mm pocket recessed into the face.  When I setu up the cam and export the GCODE the Z heights are deeper than the 3mm cut.  I have tried 2D Adaptive Clearing and Pocket.  I get Z -3.5mm instead of 3mm. 

FYI I have done the Mach 3 stepper motor calibration and it is accurate. 

(MOUNTING PANEL FINAL 529 - PANEL RECESS 3MM POCKET)
(T1  D=6.35 CR=0. - ZMIN=-3.5 - FLAT END MILL)
G90 G94 G91.1 G40 G49 G17
G21
G28 G91 Z0.
G90

While I am asking I have been unable to figure out why the G28 G91 Z0. always goes to zero. I have just gotten used to manually editing the file to Z5 to keep from messing up the work piece.

[HughesTooling]

I'd say you have the origin set wrong in Fusion, can you export the part as an f3d file and attach. As for the G28 G91 Z0.0, if you machine is home and you have limit switches it will take the Z axis to the home position. Do a search for Z0 and Mach3 and you'll find some workarounds if you don't have homing switches.

Mark

[Stuart-H]

do you need the g28 command ?

if not uncheck it in the post proceesor menu box

if Z0 messes up your part , i think you mean it drive the tool into the work you have your homeing set up upside down Z0  is at the the top , max hight and travels only in -ve to cut ( in machine coorinates )

try altering the home neg tab in homing and limits , but keep your hand near the E stop

as to the cut to deep where is z0 in your set up check the hights tab and the stock set up , as a test set the stock to have nothing extra in Z then set the Z hight to model top and see what you get then

fell for it but the other way round not cutting deep enought 

yes I uase M3 as well with all its faults 

[philRoger]

I am having the same problem. The only way around it is to edit the code and delete the G28 line, there is a similar line at the end of the routine that has to be deleted as well. It has only started happening to me since I tried a different post processor and then re-chose the Mach 3 post processor.

[philRoger]

OK I have found the problem. When you choose your post processor there is a pull down underneath that has an option to set the G28 to Null (untick). This stops the G28 code from being created.

[philRoger]

OK I have found the problem. When you choose your post processor there is a pull down underneath that has an option to set the G28 to Null (untick). This stops the G28 code from being created.