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I cut my presensitized PCBs down to size with rulers and a utility knife when I need a custom PCB.

I noticed every time I cut one, the cut is always clean, but the copper on the board at the same edge as the cut I made is uneven. In fact it curls up and that makes PCB development difficult because the board isn't 100% flat to the glass when exposing it.

Here's a picture illustrating what I am talking about:

circuit board

Currently, I use sandpaper to try to sand the excess copper so the board is as flat as possible but it wears the sandpaper fast.

Sometimes I use the utility knife at a 45 degree angle on the edge. While this often removes the curl, it also removes at least a good 30mils from the copper.

What's the best way to remove the curl without wasting a lot of PCB material or wasting any other materials? I don't think sandpaper is up to the task.

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  • \$\begingroup\$ Bench top belt sanders are very useful for many such tasks as a 45 Deg chamfer. \$\endgroup\$ – Sunnyskyguy EE75 Aug 7 '18 at 6:22
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You should use a "scoring knife" (carbide-tipped), and make pre-cuts on both sides of PCB, and you won't have this issue.

enter image description here

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I use a large metal file for that. I put the file on a flat surface and move the PCB against it. It removes copper burs and finishes the PCB material. I'll even do that to industrialized PCBs that were separated using V-scores and to remove mouse bites (tabs that keep individual PCBs connected to the panel during routing/milling).

enter image description here

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  • \$\begingroup\$ A bastard file cuts rougher and removes metal faster. A mill file will take longer but produce a smoother edge. \$\endgroup\$ – K H Aug 7 '18 at 4:54
  • \$\begingroup\$ @KH - since it is for finishing and copper/fiberglass is relatively smooth, I usually use a mill file. My lungs hate the dust though. \$\endgroup\$ – Wesley Lee Aug 7 '18 at 4:57
  • \$\begingroup\$ Makes sense. I've just used what was at hand, but that's cutting pre-holed universal board, not a printed one with actual traces. \$\endgroup\$ – K H Aug 7 '18 at 5:25
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Board houses put 'dummy' boards on top and below the boards they are machining to prevent burrs at holes, slot cuts and edges. They can afford to waste boards as the customer picks up the bill over time, but for simple stuff Ali Chen might have a better solution.

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