Mill Power Lift

For those of you doing work with a milling machine in your shops, I have something here that will drastically reduce the effort we often go through, sometimes on a daily basis. I have tried to write it in such away as to help the "electrically savvy" as well as those who might not be familiar with rectifiers. My mill, a model JMD-18 by Jet, was considered a rather topof-the-line for a Chinese manual mill, but it is probably similar to, if not identical to, those made by Grizzly and others.

Mine, sitting on and bolted to its base, is almost seven feet tall and the uppermost quarter of it, the "head", weighs close to 400 pounds.

With some effort, after loosening two large bolts on the right side of the mill head with a wrench resembling a tire tool/lug wrench, one can raise and lower the head to adjust for shorter or taller projects by using the large and heavy cast iron crank engaged in a rack and pinion on the left side of the mill (not to be confused with the spindle handles, located on the right side of the mill which simply operates the Zaxis, moving the chuck or collet up or down).

Larger and/or very expensive mills often utilize either hydraulics or a substantial gear motor to do this job or use a powered "knee" design to raise and lower the bed instead of the crank, but I doubt if many of us are lucky enough to have one of these. Eleven years ago I suffered a very severe neck, back, and shoulder injury. As I have gotten older, fighting the crank has become more and more of a chore, often causing me to choose other, sometimes inferior, options.

So, like I did on my 7" x 19" tool room lathe almost twenty years ago (American Gunsmith, December 2004), I modified it! In a nutshell, I found a low cost and readily-available gear motor I thought capable of doing the job and then modified and adapted it to my mill in place of the crank. Hopefully, with the creativity and insight of most gunsmiths, you can see what I’ve done here and make any necessary changes for your mill.

Incidentally, a buddy of mine asked me if I could similarly power the feeds moving the Xand/or Y axes of the mill table. I told him that I thought my choice of gear motor certainly had the power to do the job, but I didn’t think it could stop precisely enough for milling. There are numerous videos on You Tube for adding power feeds to milling machines, but I think they fall a little short on motor selection. And, of course, you’d have to be able to vary the power supply voltage so as to control the feed speed.

Perhaps a power supply incorporating an SCR tied to a windshield wiper motor from a large truck would work? If one of you readers is able to tackle a project like this, I think it would make an interesting and valuable article for this magazine. The heart of my project is the motor and controls from a $56 Badland 12 volt winch with a 2,500pound capacity which is often on sale at Harbor Freight.

Now call me crazy for choosing a 12 volt direct current motor, thus requiring a 12 volt power supply, but this means you have a smaller and lighter motor hung off the side of your mill and it’s easily reversible for adjusting up and down. Most alternating current motors are quite difficult to reverse, if at all.

A starter motor for a motorcycle/jet ski/snowmobile would probably work as well, but in my experience adapting the business end of a starter motor to the mill would have been far more difficult than modifying the reel of a winch. For the required 12 volt high-amperage DC power supply, I gutted my old automotive battery charger. Details to follow.

There are numerous alternatives power supplies on You Tube, including extensively modifying "switching" computer power supplies (beyond me) or modifying a power transformer from a microwave oven, which should work very well but I didn’t have a microwave to scrap! For the gear motor, the Harbor Freight winch package also includes a very nice wireless remote control, a relay and circuit breaker, and a rugged frame with

associated components that all came in handy. Making The Lift Here’s how I did it. First, I removed the cable from the winch reel, cutting it off flush at the spool using a cutoff wheel in my Dremel tool. I had a different project for putting that now-unused cable to use. Then, I removed the motor from the frame. That was easy as it involved just two screws. However, removing the reel from the frame was not so easy!

First, I removed the sheet metal shield inside the frame held in place with two small machine screws. Then, using a large punch (about 3/8") and a medium-heavy weight ballpeen hammer, I drove the front of the reel backwards and out of the bushing-lined frame. It took some care and a bit of determination, but The internally-splined, motor end is at right. The six-inch rule beside it gives one an idea of the size of the motor. after a few minutes the reel and the frame were separated.

Once I removed the aluminum alloy reel, I sawed off the flanges at each end with a band saw, sawing parallel to the reel axis, so as not to damage the full length of the central shaft or spool. This could also be done using an appropriatelysized hole saw if available, using the mill or a drill press, or even a hacksaw. The idea here is to convert the reel to a shaft or coupling which we will use to eventually connect the winch motor to the mill where the crank had been.

I carefully sawed off the flanges, apiece at a time, and then smoothed both ends of the remaining shaft in my lathe. Far The large flanges at each end were cut off to make the central shaft. Note the splined hole in the center. A belt sander or even a file would have worked as well. Next, after taking careful measurements I determined I would need to use my lathe to bore out a portion of the front end of the reel shaft to mate with the diameter of the mill/crank shaft.

The motor end of the reel shaft has female splines to fit male splines going to the motor, so you want to leave it alone. Naturally, I had to ensure that in boring what would become the mill end of the shaft I didn’t damage the castin splines at the motor end of the shaft. Attentive readers will notice small irregularities in the finished surface of the shaft.

I noticed them too, however, machining them away for cosmetic purposes would thin the shaft and the foot-pounds of torque required to deliver to the mill is unknown. Even if I went to the trouble of measuring the effort, how do we know what a "2,500 pound" Chinese winch is really capable of? I chose to leave it ugly and stronger. It can’t be seen anyway, as it’s masked by the motor’s frame.

Other than drilling and tapping the shaft for set screws, one for the splined portion and the other for the mill shaft, this completed the coupling. Note that the finished length of this new shaft also determines the spacing between the motor and the body of the mill. At the same time this determines the locations for new mounting holes in the frame for the soon to be relocated motor. Now to modify the motor frame in order to attach both frame and motor to the mill.

The frame, as is, has a one-inch hole in the outermost end. For my mill, this had to be enlarged to accommodate a large 1.5" boss on the side of the mill which

enclosed the bearings for the crank. I first tried a cheap, never used Harbor Freight hole saw in the mill. It was the perfect size but had dubious metallurgy. Not surprisingly, it gave up about 75% through the job. That frame is tough! Whatever alloy they used to make it would make an incredibly good hole saw. Anyway, about that time my mill spindle gave up as well.

However, after a couple of phone calls with some very patient This is where the crank’s (now the lift motor’s) gears attach so as to engage the teeth of the rack. and wonderful people at Jet’s customer service facility (JPW Industries, JPWindustries.com, MMCwil- I was able to get the mill back to work. I then finished the winch frame with a milling cutter, then an abrasive stone in an air-powered die grinder.

A quality bimetal or HSS hole saw here with the correct diameter would have saved a lot of work, and also probably the phone calls to MMC Williams as well. Before getting to the winch motor installed into the modified frame, this is probably a good time to go over how the frame attached to the mill body. The aforementioned boss is attached to the main casting of the mill by four large machine screws, which turned out to be 1/4" x 20 thread.

This amazed me as I would have thought a Chinese machine would use metric screws or even some other thread. Anyway, studying the geometry of my four proposed attachment points (the drive shaft, the round portion of the boss, and the now longer top two 1/4" x 20 screws through the boss) I thought this arrangement would be strong enough to handle the counter-rotational torque between the winch motor and the rack and pinion on the mill—or, to be more accurate, the pinion.

Obviously, this still leaves us to deal with gravity tugging straight down on the motor, but I figured I could deal with that later if necessary by using an angled strut underneath, however, it proved to not be needed. When scrapping my battery charger to build the new power supply, I saved the power cord, the on-off switch, and the transformer, and bought anew rectifier $2.50 on e Bay. I assembled these parts into an old aluminum box I had saved from another project together with a small muffin fan for cooling.

Lastly, I needed a pilot light to remind me to turn the power off when I got the mill head to the desired height. I had one in my "junk box" but it turned out to need six volts, not twelve. Fortunately, there was an unused six volt tap on the transformer that sufficed. Again, if you are using a microwave transformer or some other low voltage source, this would be an easy addition.

Note the output wires from the transformer go to diagonally opposite terminals on the little rectifier, and the output wires originate at the other two diagonally opposite terminals. One of these is positive (+), and the other is negative (-). Conveniently, the positive terminal was well marked by the manufacturer. Even though the rectifier is rated for 50 amps, I added a little aluminum heat

sink from my junk box under it as a little insurance policy. If you choose another motor/power supply combination, I have included a wiring diagram for reversing most any DC motor (for "Up" and "Down") using a Double Pole, Double Throw (DPDT) switch from e Bay, Ace Hardware, or wherever. Be certain, however, that your switch and wiring is rated for the amperage of your motor. Next, I had to determine where to locate the electrical relay (sole- The power supply is at top right with the motor on the left.

The relay is underneath the power supply, on the left, and the remote is high and to the right of the power supply, hanging on a magnetic hook. The two shorter lugs are for the 12 Volt AC input. Note the positive (+) output terminal at the front left. Its negative (-) "partner" is in back, on the right. noid) for the motor and where to mount the power supply.

The relay is a simple DPDT device, which upon receiving a radio signal from the remote (to go up or down) switches or reverses the heavy amperage current from the power supply to the motor. This is used because a little switch operated directly by the wireless remote could never handle the motor amperage by itself. I chose to mount the power supply on top of apiece of 2.5×3" aluminum angle with the relay underneath and used existing bolts on the mill to attach the aluminum angle. Now to mount the power supply.

Rather than drilling holes through the floor of the power supply and the aluminum angle, I chose to combine gravity with hook and loop fastener. Gravity, meaning the heavy weight of the assembled power supply, compresses Velcro on the back and sides of the supply. This was much simpler than drilling the floor of the supply for bolts to secure it and made subsequent movement for maintenance or whatever much easier.

Reattaching the boss and the aluminum angle motor/power supply assembly with 1/2" longer 1/4" x 24 bolts completed the project. It works great! I hung the little up/down remote on a magnet/hook near the right side of the power supply. Turn the power supply on, use the remote to position the mill head up or down, then turn off the power supply. Done! Oh, what project did I put that 30 feet of brand-new, leftover highstrength cable to use?

Well, it was election time and caring about the Second Amendment as I do, I had a "Keep America Great" sign in the front yard… until it was stolen! I replaced it, only this time I welded one end of the cable to the metal frame of the sign and padlocked the other end to a nearby tree, leaving about twelve feet of slack in between. A couple nights later, my wife and I returned home from dinner with a friend. The sign was lying in the driveway with its cable still attached to the tree!

I suggested we check our security cameras. Sure enough, there was a great video of a college-age female and would-be thief running off with the sign… until she ran out of cable! I’ll bet her rotator cuff was sore for a week or two, or her right arm is now noticeably longer than the left! The sign remained in our yard for the rest of the month, undisturbed, until I removed it after the election. For questions about this project, feel free to contact me at AG