Way back in history I used to get my TV "fix" from a big-dish satellite system. The ~10' diameter dish had to be pointed toward various satellites in the Clark (geosynchronous) orbit to get different channels. A ball screw actuator was used for this purpose. When I changed to a little (digital) dish, I kept all the now nearly valueless hardware, hoping it would be useful someday.
Someday came a couple days ago when I decided to try adding a powered head lift to my round column mill. The ball screw actuator motor was to be the star of the show. It was originally powered by 36 VDC, but I decided to use the 24VDC accessory power supply I already have on the mill. 24V produced about 60 RPM, which I thought would be a decent speed. One turn of the crank moves the head about ¼", so 60 RPM would give me about ¼ inch per second.
An added bonus to using this actuator motor is that the gear box includes a set of limit switches! They can be seen in the first photo. The red worm gear near the bottom is on the output shaft. It drives the gold-colored worm on the right. A tab on the nut activates the upper limit switch. An adjustable rod activates the lower one. Sweet! No limit switches to add externally, and no danger of jamming the head against a hard stop and frying the motor or stripping the gears!
Mechanically the installation was pretty easy. I first milled some flats onto the cast iron mounting plate that holds the head elevating mechanism. The surface of the mounting plate, being a non-critical feature of the mill, was predictably out of true. Then I milled a couple of flats onto the front surface of the actuator and narrrowed the ring surrounding the output shaft. Next came a couple of side plates of ~½" aluminum to connect the actuator and the plate. This photo shows the completed mounting.
The last item was a shaft to connect the ⅜" cross-pinned shaft of the actuator and the 17mm (0.690") shaft of the elevating mechanism. Being lazy, I made this out of ½" threaded pipe (~0.624" ID) and a pipe coupling. The coupling was there to provide added thickness for the setscrew threads. I screwed the pipe sections (including a stub at the far end of the coupling) together tightly, using JB weld as a "permanent" pipe dope. Cut the end of the stub off even with the end of the coupling, then bored that end of the assembly to 17mm. I made a plug of paper towels and placed it about 1" from the other end of the pipe, then filled this in with more JB weld. When it was set, I driled it out ⅜", then milled a cross slot to accept the pin in the actuator shaft. I'm not sure I really needed the fill and the ⅜" hole, but this did help align things when I was match drilling between the actuator and the side plates. The two photos here show the finished assembly from top and bottom.
I placed the switch (DPDT momentary on/off/momentary on) in a Bud box near the head locking bolts. If nothing else, this relieved me of the inconvenience of having to go from one side of the mill to the other when changing height (the crank being on the side opposite the locking bolts!)
For a finishing touch, I added a rough-and-ready scale to indicate the approximate distance between the bottom of the quill and the surface of the table. The scale itself is just a section of tape measure I had floating around. The brown object attached to the mill head is part of an old lawn chair. The bottom end gives the reading. The curved top end guides the end of the tape measure away from the pulley box. The scale is mounted to a piece of oak screwed to the column base. A piece of acrylic holds it in place. Admittedly, this kludge will not work too well if I need to rotate the head. But it's a simple matter to unscrew the scale mount.
My one concern is how long the nylon gears in the actuator will stand up to the load involved in raising the head. Things seem to be doing well so far. If the actuator fails, I can always go back to the crank. Nothing I've done to the mill is irreversible.
In any case, I plan to phone the guy who originally installed my dish. I want to find out if he has any scrapped actuators floating around. If I can pick up a couple for cheap, I expect they'll be useful for other projects.