While not actually a project you can do WITH your CNC mill, here is a project you can do TO your CNC mill for better response on the Z-axis. One of the problems with a vertical mill unless you happen to be working in outer space is that gravity makes it a lot easier to lower the Z-axis than to raise it. The stepper motor must raise the entire weight of the saddle, headstock, speed control, motor and cutting tool each time it goes up. One way they alleviate this problem on big machines is to use a counterweight that effectively neutralizes the weight of the head so that it takes the same amount of effort to raise or to lower it. The Sherline headstock/motor unit weighs about 10 pounds, which can be a lot for a 136 oz-in stepper motor to lift, particularly in 3D projects where there might be a lot of small, rapid up/down movements of the Z-axis. Harry Yingst submitted these photos of a system he came up with using a lead shot-filled tube and a pulley system suspended from the ceiling. You can probably think of some other ways too, but here is one that uses few parts, requires no holes be drilled in the machine and uses easy-to-find materials you may already have lying around. If you come up with another way, please send photos to firstname.lastname@example.org and we’ll include it.
Photos of the counterweight system show how it is attached to the mill DC motor using a hose clamp and how the line runs through pulleys attached to the ceiling to keep the weight out of the way. (Click on any of the photos to view a larger image.)
Here is what Harry had to say when he sent in the above photos:
Attached you will find some photos of my counterweight setup. The weight itself is a 9.5″ piece of 2″ PVC pipe and end caps. I drilled a hole in the center of the top one to put a screw eye through and used a fender washer and a lock nut on the inside and a standard nut on the outside. I filled the counterweight with #8 lead shot and glued it all together. (I still need to paint it.)
I used a piece of Dacron rope and connected the weight to the mill using a 3″ hose clamp and a single link of chain as an attachment point. You will notice in the picture that I used a screw-on type chain link on both ends of the line to allow the weight to be easily removed or changed if desired. I may make a second weight some day as I am considering making a second high speed milling head (30,000 rpm or more) for use in engraving PC boards, so I want to be able to swap weights quickly.