Has anyone any advice on making granulators?

I want to turn used plastic objects to a granule form again so i can injection mould with it.
Ive read what there is on here and had a question posted for a short while on a thread with no replies so thought i would ask what i want in my own thread and get a decent discussion going without the same old answer of hireing a chipper being posted.

I dont think a wood chipper either a) cuts it small enough, b) is clean and tidy enough (even if it was a brand new chipper that has had no wood in it previously the machine will still spray it everywhere), c) they are noisey and big,

So im after making perhaps a wooden box with spinning blades in it, a chute for the objects to be dropped in and a chute for the granules to fall out.
I considered having a blade spinning round on a flat sheet that has a few big holes in it so the plastic would drop through the hole and be sliced as it did so, any bigger bits get sliced up until they are small enough to fall down the chute.

Buying isnt an option, this is a hobby project and im not spending hundreds of pounds/dollars buying one, i also dont have 3 phase power and i dont agree with converters.

I am a very good engineer and can make anything so really am after some pointers, how do the commercial ones work for example?