Scraping wood: G code (fusion) doesn't lift my tool off the WCS on the z axis before moving across to start

[johndheathcote]

Special thanks to @DarthBane55  and @etfrench for helping me out on my last issue.

Scraping wood: G code (fusion) doesn't lift my tool off the WCS on the z axis before moving across to start.

Can't figure out why.  I haven't had this problem in the past (1 week in which I have owned my CNC)

Gcode seems to reflect my problem...

(1001)
(Machine)
( vendor: Autodesk)
( description: Generic 3-axis)
(T1 D=3.175 CR=0 - ZMIN=-15.5 - flat end mill)
G90 G94
G17
G21
G28 G91 Z0
G90

(Pocket1)
T1
S12000 M3
G54
M8
G0 X76.045 Y39.202             <----- moves across the area before...
Z8                                   <----- ...lifting up the tool but a little too late (right?  I don't read gcode well)
Z2.554
G1 Z1.899 F402
X76.059 Y39.206 Z1.803 F1206
X76.101 Y39.219 Z1.716
X76.166 Y39.236 Z1.646
X76.249 Y39.254 Z1.6
X76.344 Y39.268 Z1.582........

[johndheathcote]

I attached the file above.

Origin = WCS?

[Mattxer]

Seems like its an issue with your post, could you please attach it?

[johndheathcote]

Post - as in gcode?  See below.

Fusion 360 file above.

Thank you.

[will_1]

Hi @johndheathcote ,

The...

G28 G91 Z0
G90

...codes are supposed to take the machine home in Z, but it looks like your machine does not take those codes or the home position is set to a location that is below your z clearance plane which won't work for you. You might be able to change the home position on your controller. Out of curiosity what controller are you using? There may be a better post processor for you to use.

Alternatively, many of our post processors have a post property to control what codes are used for the home position called "Safe retracts" which you can set to "Clearance height". That should just use the Z value.

You also might try jogging your machine up a bit before you start if that is allowed.

Thanks,

Will Watkins

[Mattxer]

Post as in your post processor not the outputted gcode. Its a .cps file.

Will is probably right about those codes, if you know what controller it is we can help you figure out what codes are actually supported on it.

[johndheathcote]

Thank you both...

So when I start w/ universal g code sender I put my bit flush (minus paper width) on the wood in the appropriate corner.  Then I have been reseting zero... (MAYBE THAT IS MY PROBLEM???!!).  I assumed zero would be the same as wcs? whereas it is in fact a zero point well above my project?  safe from interference?

What I need to do is put the tip of my bit high in the air and reset zero THEN put my bit on the wood and then start... the program.  As you noted- it will go back to home and then run the code.  Which puts me above the project.

If you don't think thats the problem I will send the files.

[johndheathcote]

nope.  wasn't that.

[etfrench]

The first step when starting a new project is to home all of the axes.  The spindle is usually homed at the top of its travel (machine home).  Once home is established, then you touch off on the top of the stock. In some cases where the precise stock height varies, you may touch off on the machine bed.  WCS must be set accordingly.

p.s. Attaching your file to the thread will make it easier to diagnose the problem.

[johnswetz1982]

There is a difference between you Machine zero coordinates (G28, or G53) and where you have your work Coordinates (usually G54) set. You should be able to set your G54 anywhere within your work envelope with few limitations. after you set your work coordinates, you should home either your Z axis or all axis.

Noone seemed to ask does your machine have limit/homing switches? 

[johndheathcote]

I'm using the generic grbl post processor in Fusion 360 (not sure where to find the file).  I attempted the Easel post processor w/ the same results.

I'm going to return to the basics.  Gotta be me.

😂

[daniel_lyall]

Have a read of this @johndheathcote   https://triquetra-cnc.com/wp-content/uploads/2016/04/There-is-a-difference-in-Homing-and-Zeroing.pdf

99% of the time with grbl, ugs and the other flavors A quick google will find the answer but posting here is important as well.

[johndheathcote]

Thank you to all!

Ultimately I just started adding a couple lines to my G-Code and it helped me out substantially. I added a line to lift the z access before moving x&y and at the end of my code I added x0y0 then z0 to take me back.  I found some posts online the indicated this was an error in the G-Code processor but never did find inadequate rewritten post processor.

[daniel_lyall]

what post are you using.