Z depth setting in pcb-gcode

[Drools]

I'm just wondering what others are setting their Z depth to for the different thicknesses of copper. Here is what I found for different copper layers thickness.

Typical copper thickness for 1/2 oz. copper = 0.00072
Typical copper thickness for 1 oz. copper = 0.0014
Typical copper thickness for 2 oz. copper = 0.0028
Typical copper thickness for 3 oz. copper = 0.0043

Thanks

[Zig]

for double and single sided work using a 60 degree bit i set the depth by runing trial scores and viewing them through a graduated microscope. I set the width of the line to the tool manufacturers min and max limits or anywhere in between to suit the artwork requirement.

So i do not worry about depth since the isolation is main concern.


On inner layer cores i use square endmil and this is where the depth becomes critical as the core laminate is only 0.2 mm thick.

As the square endmill tool is constan width i select a tool diameter that will meet isolation requirement and only cut into the laminate at a minimum depth consistant with removing copper. I use a floating head with a threaded pressure foot which allows precise depth setting. The foot is sdjusted via a threaded lock nut.. thread pitch 1.5 mm.and a i have 72 detent notches around the lock nut periphery which gives me 0.0008" increments, a good feel for depth adjustment.
See how the numbers come out?

[Jay C]

I used 6mil for the 3oz copper I tried today.

Zig, what size square endmill do you use, and why not use it on the top and bottom layers .. is it a feed issue compared to v-bits? Are you using the precise bits or the simple v-bits like drewtronics sells?

jay

[Zig]

It is partlu a feed issue. but predominantly life of tool issue.

As for the type of V tool... a difficult answer.. I have tried plain V bits or as they are known as D bits with single cutting edge and straight two flute V bit.
I have tied LPKF cutters and now precise cutter.

So far arguably the best performer has been LPKF very closelly followed by Precise twin spiral flute cutter.

They both give excellent finish to the copper edge and money for value Precise is ahead of LPKF in the size range they both cover. LPKF does however produce a much finer ( read smaller ) diameter cutter than Precise and is specifically intended for 0.004" isolation work.

The smallest square end mill cutter i have is 0.4mm or approximately 0.016".

My price for the square endmill cutter is approximately USD 4.70 plus costs of importation.
Problem with square endmil cutter is that it must have a very keen edge to process copper too the exacting standards some RF structures require. additionally with 0.2mm thick core material used in multy layer work a less than sharp endmill will generate unacceptable ridging along the copper edge.

The reason i prefer the v bit on double side work is simply that the cutters provide a longer life than the square end cutters and there is sufficient "meat " for the V tool to cut into.

Typically i run my spindle in the 40 000 rpm regionand a feed rate below 40 mm / second often as low as 15 mm/second in order to obtain the quality of cut required.

[eSilviu]

0.1 ... 0.15mm deppending on mill bit.