If you are going to do a lot of stitching on thick leather a basic industrial machine is not designed for that. Even tho it may state it will sew leather it's not going to hold up long. You need a real leather machine to sew thick leather.
This site has one type of leather machine:
http://www.tippmannindustrial.com/pr...products_id=29
Scroll down to Leather Machines:
http://leatherworker.net/forum/
You'll also need special thread, which isn't cheap. I've done leather work for many years & you can rack up a lot of cost. If you just need to repair something I'd suggest you find someone local, like a shoe repair place, as they'll have the machine to do the job.