Deep inside cuts can be assisted by using a lazy susan – a turntable affair, similar to a cake decorating turntable.
The first question you have to ask yourself is whether you should make such deep inside cuts or redesign the piece to avoid creating such fragile shapes.
OK. You have decided to go ahead with your plan in spite of good advice. Put your cartoon onto the turntable and the glass over it. If the glass is too dark or opalescent, make a template and mark the glass. Adjust the starting point, put one hand on the glass and cartoon, and turn the glass instead of yourself to get round the score with ease.
You still have the task of breaking out the glass from the score line. This is the subject of another tip.