Tha stanly knife is the best approach. All you need to do is scribe down against a steel ruler three times and then bend the plastic at the cut. Force is not needed as it will spread the plastic outwards, as you've found out.

It will snap along the cut to perfection. Always cut on the outside of the pencil mark to allow for final light sanding (if necessary). For precision cuts then place the knife blade in the line and move the ruler up to the blade.

The important thing to remember is keep a force downwards on the ruler to prevent slippage, and loss of limbs, so choose a ruler with a handle down the centre line.

Hope this helps,

Ken

'Making Model Boats with Styrene' by the late Richard Webb (ISBN 1-900371-46-4) is a very good introductory text on working with styrene. The Stanley knife method is good especially for thicker sheet although < 2mm can be done easily with a scalpel/craft knife. With both 'score-and-break' cut techniques, you'll notice raised ridges both sides of the cut line – these can be either sanded flush or, if you're good with the scalpel, the ridge can be sliced/paired off by running the blade along the cut line – the ridge comes off as a length of spiral (like a spring).

Hi Brian I use a plastic cutter I got some time ago from "Squires Catalogue" it has a hook blade, and dos'nt give a raised lip on the cut

**LINK**

some on this site

Cheers Tom