Archive for October 23rd, 2012
Having extracted the shutter button from the camera body, it’s easy to see why the plunger causes problems:
The plunger is basically a pin that eventually deforms the top of the switch membrane. Tee’s DSC-H1 had an exposed switch, although this picture shows that membrane was still in reasonably good condition:
My DSC-H5 has a thin black protective disk atop the switch, but the disk wasn’t particularly protective and developed a dimple that held the contacts closed even with the shutter button released (which is why I’m tearing the camera apart in the first place):
The C-clip around the plunger is now plastic, rather than metal, making it less likely to erode the thin plastic shaft. Pulling the clip off while holding the button down releases all the parts:
A few measurements from an intact shutter button, which may come in handy if you don’t have one:
Mount three-jaw chuck on the Sherline table, laser-align chuck to spindle, grab shutter button by its shaft in a Jacobs chuck, grab shutter button in three-jaw chuck, release from Jacobs chuck:
That’s not particularly precise, but it’s close enough for this purpose. I used manual jogging while testing the fit with a paper shim until all three jaws had the same clearance, then tightened the jaws.
I nicked the plunger at its base with a flush-cutting diagonal cutter, snapped off the plunger, and drilled a #56 hole through the button:
For reasons that made sense at the time, I repaired Tee’s DSC-H1 with a 1-72 brass screw. This time, I used an 0-80 (which I learned as ought-eighty, if you’re wondering about the indefinite article) screw and nut, because the screw head fit neatly into the bezel recess and I had a better idea of how to smooth out the threads.
This being plastic, I used the chuck to hold the tap in the proper alignment, then turned the tap through by finger pressure. This trial fit showed it worked:
Milling the nut down to a 2.8 mm cylinder required the usual manual CNC, with repeated iterations of this chunk of code in the MDI panel:
#<r>=[[2.8+3.11]/2] g1 x[-#<r>] f50 g0 z0 g2 i#<r> f100 g0 z4
The 2.8 in the first line is the current OD and the 3.11 is the measured diameter of the 1/8 inch end mill. I started from a 5.0 mm OD that just kissed the nut, then worked inward by 0.2 mm at a time for very shallow 0.1 mm cuts:
The alert reader will notice, as did I, that the head isn’t quite centered: the cut trimmed the left side and left the right untouched, with an offset far larger than the centering error. As nearly as I can tell, the heads of those screws aren’t exactly centered on their threaded shafts, but the final result fixed that… and the overall error is a few tenths of a millimeter = maybe 10 mils, tops, so it’s no big deal.
With all that in hand, I applied a very very thin layer of epoxy to fill the threads below the now-cylindrical nut and convert the screw into a rod:
My original intent was to use the screw head as-is atop the PET shield (per those instructions) on the switch membrane, but after reassembling enough of the camera to try that out, it didn’t work correctly: the half-pressed switch didn’t activate reliably before the full-pressed switch tripped.
The PET shield I used came from the side of a 1 liter soda bottle and turned out to be 0.27 mm thick:
I think the PET shield would work with the original plunger shape concentrating the force in the middle of the shield, but the nice flat screw head spreads the force out over a wider area. As a result, the force required to close the half-pressed switch contacts was roughly the same as that required to close the full-pressed contacts; remember the nub on the bottom of the black plastic tray concentrates the force in the middle of the full-pressed switch membrane.
So I removed the PET shield, added a dot of epoxy to fill the screw slot and compensate for the missing shield thickness, then filed a flat to make a nice pad:
Reassembling the camera once more showed it worked exactly the way it should. In fact, the button seems more stable than the OEM version, probably because the slightly enlarged plunger shaft fits better in the bezel. Too bad about those scuffs on that nice shiny button dome, though:
Tossing the leftover parts seems entirely appropriate…