Starting positioning questions

[aterhune1984]

Hello, This is my first post and first time CNC-ing so please be gentle.  I have built my own cnc table and am using mach3 to run it.  I have X Y and Z axis moving correctly.  My question is...  i have g-code for a circuit board and I have a PCB material 1/32 in thick.  I try to position my milling head(dremel tip) to the bottom left corner and touching the material however once it starts moving the Z axis picks up, and X and Y move to position, the Z axis drops down slightly and starts milling above the material.  I read another post where the G-code thinks 0 is somewhere different than the top of the material.  My Z-axis is 0 at the top and -3(ish) at the bottom where it hits the base.  I am not sure how to go about changing the z-code or my configuration to have it mill slightly into the PCB to skim off the top copper layer.  Any advice would be appreciated, just remember I have come a long way to get where I am so the more detailed info you can give would be great.  Thanks!

[ger21]

The g-code is telling Mach3 where to cut.

What are you creating the g-code in?

Can you post the first 20 lines or so?

[liquidmetal]

I'm in a similar position with engraving tezt. What I do is to place my part to be engraved and manually jog the table to where I want the engraving to begin, I then zero the DRO's and look at my Gcode in the program window and program the X, Y and Z axis to what the readout of the Gcode says. In other words, the start of the program may call for X-0.125, Y0.00, Z0.200. I'll enter those values in the DRO's and then run the program. It works well for me but I'm sure there is a better way. To get to the Z axis to 0.0, I'll manually turn it down by hand with a cigarette rolling paper ( I bought a case of 5,000 of them for 4.00) between the tip and the part to be engraved. When the paper  is "caught", I call it zero. Again, it works for me but I'm sure there is a better way. MAch3 is an extremely powerful program and I'm probably using only a small percentage of it.

[aterhune1984]

here is the first lines,  this is from G code file that would be used for KCAM but i find mach3 easier to work with.  Not sure if I have to do something special to work with it.  In order to have mach3 work I remove the first two lines of code.

N001 [KCAM CONVERSION]
N002 [ORIGINAL FILE: STEPCHEAP3D - TOP COPPER.GBR]
N003 %
N004 G90
N005 M03
N006 G00 Z000.500
N007 G00 X000.187 Y000.227
N008 G00 Z000.100
N009 G01 X000.1619999 Y000.252
N010 G01 X000.1619999 Y000.304
N011 G01 X000.187 Y000.329
N012 G01 X000.239 Y000.329
N013 G01 X000.2640001 Y000.304
N014 G01 X000.2640001 Y000.252
N015 G01 X000.239 Y000.227
N016 G01 X000.187 Y000.227
N017 G00 Z000.500
N018 G00 X000.262 Y000.377
N019 G00 Z000.100
N020 G01 X000.237 Y000.402
N021 G01 X000.237 Y000.454
N022 G01 X000.262 Y000.479
N023 G01 X000.314 Y000.479
N024 G01 X000.339 Y000.454
N025 G01 X000.339 Y000.402
N026 G01 X000.314 Y000.377
N027 G01 X000.262 Y000.377
N028 G00 Z000.500

[ger21]

The g-code is telling the Z axis to up to 0.5 then down to 0.1. It'll never cut if you set your Z zero at the top of material, with -Z going down.

If you created the code, you'll need to learn how to set it up so Z zero is the top, with -Z going down.