Nice job. I bought an off-the shelf one, works a treat and I have chopped up literally hundreds of branches using it now. Yours is probably a lot stronger though.
I was going to build one but got one off eBay for £25 delivered so it was not worth getting the gear out, I bolted a piece of flat bar with the edge sharpened to the bottom where the wood rests, it gives it a bit more grip. I'm going to modify the adjustable part as well eventually.