How to set ZERO and a few more questions (PCB use)

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27 Jun 2013 15:36 #36120 by yello
Hi,

the main use for the CNC for now will be isolation milling to make PCBs. For PCB isolation milling I need to just remove the top copper layer, thickness is about 0.035mm.

But my question are rather general question about LinuxCNC and the machine use. First, before you ask, to design the PCB and generate the Gerber data I use DesignSpark (a free tool for electronics design), to convert the PCB Gerber to Isolation G-Code I use PCBMill (from cncdrive.com - both are freeware).

Questions:
How to set the Z axis after touch?
Lets say I set the Z-axis to touch - and I want the program to run at about Z-axis touch - plus (or minus?) 0.3mm after touch? How would I do that?

Can a set a fixed X/Y Zero? And if so, how?
Now I fix the laminate and then basically search a good place to start with.

Can the between 'jobs' travel be faster?
When the tool is going from one cut area to the next it has the same speed as the cut speed, can that be sped up?

Really important to me is just the setting of the Z-axis. Others I can live with.
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27 Jun 2013 16:17 - 27 Jun 2013 16:33 #36123 by cncbasher
you touch off to the top surface of the pcb and set this as zero ( see touch off button and values in axis )

your program that produces the gcode will set the amount to mill as a negative value i.e - 0.3 or it will be a configurable value set in your post processor

in pcbmill under the settings tab is where you can change these values
i.e Z mill depth -0.1 change this to suit your requirement

make sure this value is a negative value
you can set also the start point my moving your x and y and then setting touch off for these values to zero
this is usualy the bottom left corner , but can be any point you chose
Last edit: 27 Jun 2013 16:33 by cncbasher.

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27 Jun 2013 16:36 #36124 by yello

you touch off to the top surface of the pcb and set this as zero
your program that produces the gcode will set the amount to mill as a negative value i.e - 0.3 or it will be a configurable value set in your post processor

in pcbmill under the settings tab is where you can change these values
i.e Z mill depth -0.1 change this to suit your requirement

make sure this value is a negative value


Seems you know PCBmill :)

So I would do the 'touch' in LinuxCNC and then go up, let's say 1

And in PCBMill set the Z travel height at 1 (same as I went up in LinuxCNC)
and the Z mill depth at -0.3

Is my thinking correct ?

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27 Jun 2013 16:47 - 27 Jun 2013 16:48 #36125 by cncbasher
yes your correct

once you set your depth in pcbmill , and set zero to your top surface , linuxcnc will remember this value while the machine is on ( you will need to set this touchoff each time you switch the machine on )
but whilst it's on , you should not need to touch again

travel height is set at 1 in pcbmill this tells it to give 1 unit of clearance between moves , so as the top surface is zero , if your using metric then it will lift up 1mm above surface
between moves

the drill z level is for setting drill depth which of course is the thickness of the pcb + a small amount to make sure your right through the pcb ( don't forget a scrap piece of board or mdf below your pcb )
that can be discarded once in a while as it acts as a sacrificial surface for drill holes or milling slots etc or edges
Last edit: 27 Jun 2013 16:48 by cncbasher.

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28 Jun 2013 15:52 #36148 by yello
I think it's not working that way, but this way:

I do the 'touch' in LinuxCNC and set depth to 0.3

And in PCBMill set the Z travel height at 1 (same as I went up in LinuxCNC)
and the Z mill depth at -0.3

I guess from here onward the CNC will take the Z travel hight (1) from the G-Code.


BTW, is there an easy way to go back to the start position, that is that position were I homed all 3 axis?

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28 Jun 2013 16:33 #36149 by cncbasher
if you want to get to the point you have set zero
issue the command G0 X0 Y0 Z0 in the mdi window

you can add a button to an axis panel with this preset if needed
see the pyvcp sample panel xyzjog.xml

once you have set your zero points linuxcnc will remember this until the machine is switched off , all moves in your gcode are referenced from this point

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28 Jun 2013 17:42 #36151 by BigJohnT
You might want to read the tool touch off tutorial on my web site.

www.gnipsel.com/linuxcnc/g-code/index.html

JT

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