Interestingly I'm now increasingly moving away from pencil sketches. I do still take photos of knives for "inspiration", but then as long as I have one dimension (such as length) Inventor will scale my trace of the photo.

The reason I've stopped pencil sketches is because they've sort of become redundant: I can now do first draft designs just as well in Inventor, and I suppose the interesting thing about the workflow is that we need to then prototype possibly through several iterations, as it's about feel & heft more than paper dimensions - with the exception of e.g. a bolster, we have no 'tolerances' as such.

We've tried various materials other than steel for this, but since they weight less or have other properties too different from steel you can't really get a feel for it. The other advantage of using a low-cost stainless steel for prototyping is that then all the other processes (mainly heat-treatment and finishing) can also be run through.

However I'm thinking of trying to make some friction-held folding knives as a learning exercise. I have got some excellent templates in a couple of books and it had occurred to me how to get those slightly complicated shapes in accurately - scanning them in with a tracing paper grid overlay solves a lot of problems!