I score it using a steel rule or square and a carbide-tipped tool designed to score tiles. This is similar to the tool I have; http://www.toolstation.com/shop/HandTools/TilingTools/d10/sd240 For single-sided, score the copper side first; when you turn it over you can see the score through the fibreglass so you can line the second score up. Double-sided just needs some careful lining-up. I use home-made "bending bars" (also used to bend sheet metal) to crack the score. It's just two pieces of steel angle; mine are about 20" long, made of about 2" x 2" x about 1/4" thick. There's a bolt at each end to clamp them together; this helps if large sheets require offsetting the bars in the vise. The bars are useful to clean-up the ragged edges that result from scoring/breaking. Clamp the sheet in the bars & file one edge down to the level of the steel. This is now the "master" edge and the others can be similarly filed square by using a small square (shown in the photo) to ensure that the master edge is at 90 degrees to the top of the bars. The top surface of my bars shows the results of several years of filing. Precision work such as making precise panels and drilling & cutting apertures for meters etc is done in the milling machine; small carbide endmills (I bought heaps from an ebay trader called, iirc, Tools & Tunes many years ago) as used in PCB factories are used.