I built a small scale trimmer some years back but alas have no pics so you will have to bear with my awful use of paint so I can attempt to explain how it goes.
Now I want to say that this device is in no way approved by anyone, anywhere, not even me - in short, it can be feckin dangerous
You will need....
A food blender (speed control option preferred)
A plastic tube (middle of shrink wrap ideal)
A dustbuster (other handheld vacuum's are available)
Various tools, araldite, patience also required.
Click to view attachmentTake your blender and remove as much of the plastic beaker as you can (dremmel multi did the job) so you are left with similar...
Click to view attachmentI then got some mole grips and bent the 2 flat blades up at 90deg ready for the tube to slide over them. This I found to be quite fiddly as if the blades were not centred then the whole unit shook wildly. In this 4 bladed pic, you would bend the 4 blades up towards you as even and straight as poss.
Click to view attachmentCut plastic shrink wrap tube to approx 6inches and then cut/melt a slot approx 80mm long by 3mm wide. The wider the slot, the shorter it will cut as you can get the buds closer to blades. The slots location must tally up with where the blades are.
Click to view attachment Click to view attachmentOnce I was sure that the tube was sitting perfectly, I added a whole pack of araldite strengthened with small angle brackets to hold things solid. I made a cradle for it lay horizontal in and so I could strap it to my workmate and then fitted the hose from the dustbuster to suck away the trim
Click to view attachment Click to view attachmentIt did work surprisingly well, the bud was simply dragged over the slot, the leaves were sucked in, chopped off then spat into the hoover for hash recovery at a later date but I never quite trusted using it and it was a bit too noisy for my liking.
If I was to get another blender, do you think a variac could be used to slow the blades and quieten things down?
Cheers