hi dan like tweekie said you have to have the pulleys tight on the shaft. the shafts have to line up.you cant have to much friction .Dont forget you are talking motors with oz. inch of torque not horse power. If you dont get the machine right you will through up your arms and give up saying cnc is no good for you. And that would be a lye. If you get the machine working right you will be proud of it and will be boasting all over the place about how well you machine works. That is the reason there are so many people on these forums . WE ARE ALL PROUD OF OUR MACHINES AND THE WORK WE CAN DO.. It doesnt matter if you use wood or metal for the build as long as the electronics and mechanicals are the best you can do. So be paitient and take your time with the build in the end you WILL have a good machine. Check with a company called SDP/SI at
www.sdp-sl.com they have catalougs with pullys belts etc. good place Oh and by the way hope you are using timing pulleys and belts other wise you will never time your machine...