Holding copper clad board flat

[Pat]

When using a V-Bit to cut traces my biggest problem is uneven board height. Where the board surface is higher the V bit cuts wider and where the surface is lower it cuts skinnier. My first few attempts didn't work all that well as I'd have both wiped out traces where the cuts were too wide and and shorts where they weren't wide enough. I could reliably cut DIP boards with 20 mill traces and one trace between DIP legs but that was about it.

Single sided copper boards naturally cup towards the copper side and I find that I can use several screws around the perimiter (just the side of the screw head pressing down on the board edge, not through the board). As long as I don't tighten the screws too much the board lays very flat. Its a bit finicky but I find that once the board just touches the bed surface an additional 1/16th or so of a turn works great. Too tight and the center of the copper clad board pushes upward.

Double sided boards are a different kettle of fish as both sides are under tension and the board can have ripples. I tried building a vacuum table using a shop vac but there just isn't sufficient vacuum to hold the board flat.

Since then I gave up on V-Bits and use micro end mills (normally 0.01") where cut depth doesn't affect cut width and its working great but I'd still like to find a better way to flatten out the copper clad boards.

Any thoughts or experiences?

[gavilan]

Instead of controlling the flatness of the board I'm compensating by probing the surface of the board before milling it. You can see my results and the whole process in action here:
http://tv.onshoulders.org/

I hope this helps. I got the idea from Poul-Henning Kamp on his website:
http://phk.freebsd.dk/CncPcb/index.html

[admin]

When using a V-Bit to cut traces my biggest problem is uneven board height. Where the board surface is higher the V bit cuts wider and where the surface is lower it cuts skinnier. My first few attempts didn't work all that well as I'd have both wiped out traces where the cuts were too wide and and shorts where they weren't wide enough. I could reliably cut DIP boards with 20 mill traces and one trace between DIP legs but that was about it.

Single sided copper boards naturally cup towards the copper side and I find that I can use several screws around the perimiter (just the side of the screw head pressing down on the board edge, not through the board). As long as I don't tighten the screws too much the board lays very flat. Its a bit finicky but I find that once the board just touches the bed surface an additional 1/16th or so of a turn works great. Too tight and the center of the copper clad board pushes upward.

Double sided boards are a different kettle of fish as both sides are under tension and the board can have ripples. I tried building a vacuum table using a shop vac but there just isn't sufficient vacuum to hold the board flat.

Since then I gave up on V-Bits and use micro end mills (normally 0.01") where cut depth doesn't affect cut width and its working great but I'd still like to find a better way to flatten out the copper clad boards.

Any thoughts or experiences?

This works great and it easy:
http://millpcbs.com/index.php?option=co ... &Itemid=63


He's an example of what I did today using that method. viewtopic.php?f=5&t=55