Swing Arm Light for the Mill
© Frank Ford 2009; Photos by FF                                                  Please click the small photos for a better look.

This is yet another of my projects that basically "flowed" along. OK, maybe it was more my typical herky-jerky gait, but what I mean to say is that while I planned to make this arm thingy, I hadn't worked out the exact design, so I started with what I figured would be the fun part - the joints.

I had this nice hefty piece of aluminum salvage that had some interesting holes in it. Interesting enough I planned my joints around the holes, because was going to make two lap joints, and there were four holes each placed at the same location in relation to the corners of the piece.

Cutting the piece in half, using my shop-made fly cutter:


Squaring up the halves:


Drawing the joint lap area:

I just set my divider to scribe the largest circle around the existing holes and since the holes were at the same distance from the edge, things worked out nicely


I then drew 45-degree lines from the tangent of the circle out to the opposite side of the piece, and similar lines inward to leave me a square straight section:


Cutting on the bandsaw, I roughed out four blanks:


Most of the time, I have my tiny Rusnok mill set up with a rotary table on which I've mounted a fixture plate. (I'll have to do a piece on that sometime."

The best feature of my fixture plate is that it has a nice 3/8" hole in the center with a 1/4-20 tapped hole in its center. I can easily make little spuds to plug into that hole so I can locate parts easily.

First, I turn the spud to fit the hole in my joint, and then turn the other end to 3/8" to fit the fixture plate. Here I'm just trial-fitting my turned piece:


Now all I had to do was plug the piece onto the spud, clamp down, and I was ready to radius - no measurement needed:


Just by eyeball, I cut the outer radius of each piece. Notice I have the joint piece clamped onto a 3/16" thick piece of sacrificial aluminum to avoid hitting the fixture plate:

The 1/4-20 bolt holds the part down at the center, so I needed only one other clamp at the end of the piece:



Back on the big mill, I finished off the section of the joint that would lap over the other half:



At this point, my pieces became two right-handed and two left-handed ones. I milled the ends to be a tight fit into the thick walled aluminum tubes that would be the arms of my light bracket:


After a few tries, I got a really tight fit:

Before driving the arms onto the joints, I tapped one section of each joint, and drilled the other for bolt clearance. One part I didn't photograph was making some thin HDPE friction washers to place between the joint pieces and under the big headed bolt that was to hold them together. Friction would be adjustable with that bolt, and a jam nut bearing on the threaded section of the joint.


Ok, time to make a big headed bolt for each joint. I turned and threaded both ends of a nice big steel rod:


Then I had a double ended bolt, which I cut in half:


I turned the head to a tapered washer-like shape leaving a bit in the center to form a hex head using the mill and a collet block:


Back on the lathe for a bit of finishing:


Here are the bolts, ready to use:

The completed joint:


I started this project with the idea of using my existing lamp head. It's a short one I'd bought on sale from Grizzly, and mounted to a temporary wood arm. Temporary, as in the sense of being in use for three years until I finally did this project. You can see it in the piece on my Mill Light Bar, on which I mount various things that are handy at the milling machine.

At the very last minute, I realized how I'd be sticking this thing onto the hollow alumunim arm. I'd modify the original base, so I could take advantage of the swivel positioner:


Getting, er, "creative" with my push sticks, one under the tapered end, one to push forward, and one to hold tight against the fence, I safely and neatly sliced off the part I wanted to use:


Gripping it with "less than ideal rigidity," I milled the tapered piece to fit into the aluminum tube:



After drilling and tapping for 4-40 screws (a good job for the mini hand tapper) I finished up the attachment:


Right then the light went on. Not that light - the one in my head that had been burning rather dimly of late. I just realized I'd only needed one arm joint to complete this project because I'd saved the one from the original base. Oh, well, now I have an adjustable friction joint for another project. I refuse to disclose how many such leftover items I've made in the last few years!

Once it was assembled and wired, I was glad I'd done this job. I keep the pivot quite loose at the light bar end, so I can simply bat the entire rig over to the left without changing the light angle. Then when I want it close, it swings right into action. Because the arm joint and light bar pivot end are fixed paralell to the floor, there's no tendency for the head to droop downward even if the pivot and joint are both quite loose. I have it set so he middle joint is movable, and the one at the light head is quite tight. That's the system that works best for me.


Here are some "action" shots:

Up close:


Swung way back out of the way:


Around to the right:


In front:


Folded against the bar, asleep:




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