The most important factor when v-cutting is to leave a smooth cut. If you hack away and leave cuts INTO the plastic (i.e. the start of a crack) then that cut will slowly grow and grow as you use the skates.

Begin by folding a piece of paper in half. Starting at the folded edge, draw HALF of the shape that you want, so that when you unfold the sheet of paper (after you have cut along this drawing) you get a symmetrical shape. Try to make a few shapes, with varying depths and widths to try.

Place the cut out shape on the back of the cuff, and check how much material you will actually be removing. It might be a good idea to compare this to an already v-cut cuff (e.g. on Remz or newer USD models) to check that what you have planned is what you want.

Grab a pencil (or anything else that will mark plastic) and draw along the shape on the cuff. FOr the actual cutting I recommend a disposable scalpel/modelling knife. I bought a pack of 10 from my local poundland for £1.

Start cutting a few mm's away from the drawing, leaving a bit of room for later, the main aim to begin with is to remove the material inside the drawing, but leaving the lines you have drawn intact. It may be a good idea to use something like a junior hacksaw or a jigsaw for this, as its very hard work with a knife.

Once you have removed most of the material, begin slicing thin layers away with the knife until you reach the line you have drawn. Make sure that you leave a smooth surface, otherwise the cuff will eventually crack.

Use the same shape on the other cuff to ensure you get two identical cuffs.

I have done this on 4 TRS cuffs, which are easy to cut because they're thin, and 2 USD/Razors cuffs which are thicker and require more 'work'.