I fixed mine at TechShop.
Small sheet of 16 gauge mild steel
Brazing rod (if you have an oxyacetylene torch) or JB Weld (epoxy)
Drill press + bits
Oxyacetylene torch if brazing instead of using epoxy
Step 1: Take Some Measurements
If you want to reuse the old thumb screw used to close the clamp, you'll have to measure the outside thread diameter of the screw (in order to be able to make a hole through which it will fit). It may be easier to buy a matching nut-bolt combo, but I liked the thumbscrew, so I kept it and found a nut to match its diameter and thread pitch. I did have to do a little bit of touch-up work with a file to the threads of the screw in order to get a smooth enough action so it could turn without the aid of pliers.
Step 2: Sketch Out the Template
It is hard to see the scribed lines in the photo, but I divided the scrap of mild steel into five sections. The middle section will contain the hole that attaches to the lamp, and one of the end sections will have a hole through which the thumbscrew will pass.
I went ahead and used a center punch to put a dimple at the center of each hole.
Step 3: Trim the Stock to Size
Step 4: Punch Out Any Holes That You Can
The turret punch I have access to had a punch that was appropriate for punching a hole for the thumbscrew. That size need not be very specific, as long as it is larger than the outside thread diameter of the thumbscrew.
I needed a hole larger than -.38"
and punch 'F' was .5:
Good enough. Punched. Done.
Step 5: Drill Any Holes You Couldn't Punch
To keep the hole from wandering, it is best practice to start with a small hole and then step up through a couple drill bit sizes until reaching the full diameter.
I finished with a size 'S' bit at .348 (pretty darn close to the .349 measurement of the lamp's post).
Step 6: Bend the Clamp
I opted to make the clamp using four 45 degree angles to give it some arc instead of two 90 degree angles. That will help hold the lamp somewhat away from whatever it is clamped to, giving a wider range of motion and reducing the risk of fire from the hot bulb coming in contact with, say, a wooden shelf to which the lamp was clipped.
I put a 45 degree bend on each side of the middle section. At the end of the second bend, the two sides of the clamp should be at 90 degrees to each other, giving an easy way to tell if things are properly aligned.
An additional 45 degree bend on each side completes the shape of the clamp.
Step 7: Attach the Nut to the Clamp
I had intended to braze the nut to the outside of the brace, allowing the largest opening possible between the jaws of the brace. However, when I heated the metal elements and introduced the brazing rod, there was a HUGE *pop* and the brace and nut were covered in a quite thick, almost crystalline, layer of white powder.
At the time I was attempting this, my understanding was that zinc could create toxic fumes when heated/welded, and this sudden conversion of metal to powder made me wonder if I might not be brazing steel to steel. In the interest of self preservation I stopped the brazing attempt. I dug through the trash and found the little baggie that the nut had been sold in, and sure enough it was listed as 'zinc plated'. Having now done some non-scientific online research, I don't think the zinc plating was the root cause of the pop (more likely the metal was too hot for proper brazing), nor do I think that the zinc plating from one nut would have caused me any ill effects had I continued to attempt the braze. I was using a fume extractor, but one braze would have probably been fine even without that.
As I was pondering the zinc issue, I happened to test fit the post of the lamp into the drilled hole in the clamp, and it was such a good fit that I couldn't get it back out without damaging it. Attempting to braze the nut to the clamp again would certainly melt the post of the lamp beyond usable, so brazing was suddenly not an option, zinc or not.
Anyway, I shifted my plan of attack and used JB Weld to attach the nut to the INSIDE of the clamp. Flipping the nut from the outside to the inside of the clamp when switching to metal epoxy instead of brazing may have been overkill, but it ensured that tightening the thumbscrew could not possibly cause the epoxy to detach since it would be a compressive force. Fortunately I didn't really need the space that I lost by moving the nut to the inside.
Use a bench grinder to round off the sharp corners, and you're done!