Archive for January 11th, 2012
While I was rebuilding the HPB heater wiring, I drilled / countersunk / tapped a 4-40 hole in the middle of the aluminum sub-plate for a screw to secure the middle of the heater PCB:
Remember: this plate is firmly secured to the plywood build platform with three leveling screws over springs. Another aluminum plate, with Kapton tape as the build surface, sits on top, providing an absolutely flat build platform. If you’re using a single plate, you could backfill the hole with a dab of JB Industro Weld epoxy atop a lightly greased screw, then file the top flush with the plate.
A flat-head screw harvested from a chunk of electronic junk came from the Drawer o’ Short 4-40 Screws and fit perfectly:
Mirabile dictu, the screw was short enough that it didn’t require any trimming to stay below the top surface.
Securing the center of the PCB to the aluminum plate cuts the heater’s free span in half: the PCB originally had screws only along the left and right edges. Its thermal expansion visibly bowed it away from the plate and I hope this will reduce that problem. Of course, now the PCB’s expansion has nowhere to go and those thermal stresses will probably begin chewing up the mounting holes.
While I was at it, I removed the MBI “heat spreader” tape from the PCB. I’d been reluctant to do that, for fear of peeling the traces right off the board, but the surface was in fine shape. Whew!
More on the wiring and epoxy blobbed brass tube later…