Halogen Desk Lamp: LED Floodlight Retrofit

Quite a while ago, I rebuilt a gooseneck shop lamp with an LED floodlight module, the light from which appears in many pictures of the Sherline mill. That module has a sibling that I just combined with a defunct halogen desk lamp to produce a better task light for the bench; the original 12 VAC 50 W transformer now loafs along at 4 W and ballasts the lamp base against tipping.

My initial idea, of course, was a 3D printed adapter from the existing arm hardware to the LED module, but PLA gets droopy at  normal high-intensity LED heatsink temperatures. That led to doodling a metal bracket around the LED module flange, which led to pondering how annoying that would be to make, which led to the discovery that the screws holding the LED plug to the heatsink were ordinary M2x0.4 Philips head, which suggested I could just screw a bracket to the back of the module, which brought a recently harvested aluminum heatsink to hand, which led to the discovery that the tip of the pivot screw fit perfectly between the fins, which …

Shortly thereafter, I milled off the central fins to fit the shaft of the pivot screw, introduced the heatsink to Mr. Disk Sander to bevel the bottom, sawed the threads off the pivot, press-fit the two together, drilled a 2 mm cross-hole into the pivot, buttered it all up with epoxy, jammed a short M2 screw into the cross hole, and let the whole mess cure:

Desk Lamp LED Adapter - top view
Desk Lamp LED Adapter – top view

The lamp modules were a surplus find, with one pin clipped nearly flush to the insulator. I soldered a pair of the same male pins as in the battery holders, with the matching female pins as a crude connector. The unshrunk heatstink tubing isn’t lovely, but got us to First Light:

Desk Lamp LED Adapter - front view
Desk Lamp LED Adapter – front view

The original counterweight is, of course, much too heavy for the dinky LED module, so I’ll drill the mounting hole for the vertical arm further back on the beam to get another foot of reach. That will require more wire between the transformer to the lamp, soooo the connectors might just become soldered joints.

As you can tell from the background, Mary snatched the lamp from my hands and put it to immediate use in The Quilting Room.

The original doodles bear no resemblance to the final product, but do have some key dimensions that (having discarded the unused hardware) I’ll likely never need again.

The pivot between the arm and the lamp housing, with an idea for the LED holder:

Desk Lamp Bracket Dimensions - doodle
Desk Lamp Bracket Dimensions – doodle

Details of the repurposed heatsink and the pivot bolt, with a block that never got built:

Desk Lamp Heatsink Dimensions - doodle
Desk Lamp Heatsink Dimensions – doodle