Sorry I'm late to the party here guys. Shaun - spend some time looking through the rest of Dan Comeau's site (where MotoMike linked plans:
http://dcknives.blogspot.com/ ). There is a TON of info there both on general build tips/suggestions as well as more specific info on things like motors. I set mine up with a treadmill motor and a set of controls I rigged up based on this video:
.
My thoughts on this motor option are:
1) it actually works really well - but WILL die as metal dust is sucked into the motor. To mitigate this I have a system of filtration set up which so far seems to be working
2)if you go the free motor route, check it before installing! My motor dies a while back, but that was due to excessive wear on the brushes, which I suspect was simply down to getting a treadmill from a *really* fit dude who obviously used the thing more than normal humans would.
3) when my motor dies, I will replace it with a 3 phase motor with VFD for speed control, so if I were to build another, I'd just go straight to that option if I could afford it
As for challenges I ran into, there were a couple.
First is alignment. I somehow screwed up the alignment when I welded the motor mount, and so it's a little off. I'll have to fix that as it makes the whole system less stable than I'd like (belt tracking in particular is a challenge)
Second is wheels. Due to the expense of shipping/customs from the US, mine was built with longboard wheels. Recently I found this seller on ebay:
https://www.ebay.ca/usr/portcollector?_trksid=p2057872.m2749.l2754 and bought a set of aluminum wheels that will replace the plastic ones. Just wanted to flag a Canadian source for you. They look really well made and I had good service from them.
I'll likely think of other things too...
Good luck with the build! It is a GREAT tool to have, and even better when you've made it yourself.