Joe,
Yep, you have run into a couple of problems with
boards being level. It has been found the boards
will "bow" up in the middle when clamped on the
edges and FR$ has (I think) a 10% tolerance for
board thickness. The best way to hold down the board is by vacuum.
As for the "paper" board, you want CEM type as
opposed to the FR4. I get mine from a seller on
Ebay
(<
http://stores.ebay.com/PCB-Laminates-Copper-Clad?_trksid=p2047675.l2563>).
There are a few "autoleveling" packages that
probe the board height before doing the isolation
milling and these seem to work quite well. I use
Eagle and a ULP called pcb-gcode.ulp with autoleveling to make my boards.
For fine work, I use a 30° V bit, and for general
non critical stuff, a 60° one from <
http://www.drewtronics.net/>.
HTH
Art
Country Bubba
At 09:01 AM 12/13/2012, you wrote:
>Hello,
>
>I am trying to mill the pcb (FR4) with a taig.
>
>I did not have much luck with a uniform trace isolation even when I hold
>the board flat down by clamping down on the board edges. It appears that
>the pcb surface might not be uniform and that might be the reason why I
>cannot remove/mill out the copper layer consistently. I read about using a
>foot (http://hackaday.com/2011/04/22/pcb-milling-tutorial/) to push the pcb
>down while milling, but, that was a bit too much for my skill level.
>
>I read somewhere that it is easier to just paint the whole circuit board
>with some paint and then remove/scribe the paint off wherever the traces
>were being milled. This process is described here:
>http://reprap.org/wiki/Scratch_n%27_Etch_PCBs . Just wanted to check if
>anyone has experience with this?
>
>On a different note, I read that "paper phenolic" boards are better/easier
>on the mill and drill bits. I checked digikey and mouser and could not come
>up with any "paper phenolic" boards. Wondering if anyone knows of a
>supplier for "paper phenolic" boards?
>
>I used the EM2E8-0625-90VC bit from
>http://www.precisebits.com/products/carbidebits/scoreengrave.asp to mill
>the board. Maybe, I need to use a 45 degree bit as noted in this article:
>http://millpcbs.com/index.php?option=com_content&view=article&id=23&Itemid=47
>
>Any thoughts or advice, please?
>
>Thanks
>Joe