[sdiy] Cutting PCB Material

[Magnus Danielson]

From: Scott Gravenhorst <music.maker at gte.net>
Subject: [sdiy] Cutting PCB Material
Date: Fri, 02 Nov 2001 15:57:42

> I need to cut a piece of pre-etched PCB in half so I
> can use the other half for something else later.  The
> package says "polyester glass".  I think I read
> (here) that this stuff is really abrasive and can wear
> out tools for cutting??  My intention was to use a coping
> saw, which is really the only tool I have for this other
> than simply holding it against a table edge and breaking
> it along a line of pre-drilled holes.  The material is
> cream colored if that makes a difference.  Will this
> ruin my saw blade?  The cut will be a little longer
> than 4 inches.  (René, I'm finally putting the 4069 VCO 
> on a permanent board!).

There are a few things you can do:

1) Cooling. You are cutting through a hard material, this converts
   your applied force into heat. That heat softens the blade and the
   applied force does the rest. It is comparable to that of cutting
   through metal. I am not an expert on practical mechanics, but I am
   sure that someone with more of those skills will get the right
   triggers by this.

2) Weakening the material and then break it.
   This is an old trick. In PCBs like this the fibers are woven into a
   mesh. If you weaken the material along one of the fiberlines
   (actually between two of them) by cut into it alongside a ruler you
   can then quite easilly break it, since this introduced faultline
   will see more stress when you bend it then other parts of board. If
   you flex it in both directions multiple times, you let the
   faultline grow bigger and bigger and suddenly it is almost done.
   
   You can also drill, but the fault-line concept has the benefit of a
   rather narrow breakdown area. If you want to narrow the disaster
   area (which may be crackled) you need to narrow down the distance
   between the holes and also the size of the holes. If you create the
   faultline and then drill, you migth quicken the process.

   Remember, if you drill you *also* have to do cooling.

I use the faultline method on those predrilled pertinax boards, for
smaller things I only need to start the fault line by a cut in the
edge, since that creates sufficient amount of faults into the matrix
and the predrilled holes do the rest, bending it of is quickly done.

This later technique is used in sewing to cut open a rift. You simply
cut in a few centimeters, then you just pull them appart. It goes much
quicker than cutting, and it is straigth!

BTW. Bob Moog did his PhD dissertation on the study of fault locations
in NaCl crystals under pressure. He used ultrasounds from 5 to 150 MHz.

Cheers,
Magnus