Sherline Milling Machine With PacSci Steppers
Generally, CNC retrofitters for Sherline milling machines use ~65/oz surplus stepper motors. Since I wasn't sure the Sherline was going to be large enough to do the kind of work I needed, I opted to go with 210/oz PacSci stepper motors. These units have the same 1/4" shaft that the cheap 65/oz motors have as well as the same size mounting flange. I have found that the 210/oz motors have worked out very well and can't imagine using motors with lower torque. I can cut 5" a minute with a 3/8" end mill and never loose a step. The motors are 200 steps/rev and with the AhHa! controller I run them in microstep mode at 1600 steps/rev. Very smooth, quiet, powerful operation. I highly recommend these steppers for the Sherline.
The motor mounts I used are from the AhHa! Sherline Motor Mount Kit. This kit is a bit pricey, but I have found that it was worth it. The mount is machined out of a single piece of 1/4" aluminum channel and is very ridged. The kit also comes with awesome helical, clamp-style shaft couplers. Again, I highly recommend these. The whole kit looks like it was just made for the Sherline mill it installs so nicely. Then again, I guess it was...
The limit switches were a lot of work to install and I have found them to be of limited use. The Sherline mill is so compact that there really isn't a lot of room to mount the switches anywhere. I ended up making a number of small brackets from 3/4" aluminum angle in most cases. I'd probably leave them off if I had to do it all over again.
If you've ever seen a Sherline mill before, you were probably wondering what that goofy looking thing over the motor was. Since I mill 3 parts at a time, and a good portion of the 2.1 hours it takes is cutting pockets with a 3/8" end mill, I was having problems with the drill motor overheating. The bad part of the overheating was that the electronic control circuitry for the DC motor would shut the motor off!! You guessed it, the CNC gear would continue to move the table. Not good! Rather than slow the cutting rate down (!) I went to the local Radio Shack and purchased a 65 CFM muffin fan. Next, I made a bracket out of 3/4" angle aluminum to hold the fan right above the motor. The fan actually sits right on the top of the motor and the top of the motor support the center of the fan. It works amazingly well at keeping the temps down. I noticed that a lot of the air from the fan wasn't really blowing on the motor, so I made that really sexy shroud out of some .032 sheet aluminum. Now the motor runs only slightly warm even towards the end of a 3 piece run!
Since the parts that I need to machine are 2.5" square, the standard table of the Sherline wasn't quite large enough. I added two strips of 2.5" x .5" aluminum extrude to the table with 10-32 screws, and then machined out female slots that would fit the parts I needed to machine. Works great!