Isn't that simply an eccentric disc on the shaft that binds against the rail when you turn it?
Well, that’s a much better way of putting it than I did. Yes, it is.
Isn't that simply an eccentric disc on the shaft that binds against the rail when you turn it?
Look for a drift pin that should secure the disc to the shaft; maybe it has sheared-off and allows the disc to rotate on the shaft rather than turn and bind against the rail.
If it were simply pressed onto the shaft, it might have stripped splines. See if the disc will spin on the shaft a bit.
If this is the case, you should be able to figure out the position of the disc relative to the shaft where it would work and drill a hole through the disc and shaft and drive a pin into the hole to hold them together.
Is the disc lose? Even a little bit of play will negate the clamping ability. If the wheel clamped too hard, it would warp the rail.
I'm going to give this a shot... excuse the very crude mark ups. Eccentric round portion is supposed to live inside the red notch. When lever is tightened (to lock focus), the bottom edge of the plate yellow mark is pressed towards the "fin" that slides in the kerf(slot) on the side of the bed. In my 8x10 sample, there is almost zero left to right play in the focusing knob/rod and locking assemblies.
The plates definitely move. I'll be darned if I can tell which part of the mechanism is actually doing the work though. I may pull the main plate off and see if that lets me see what else is going on in there.
brienentz is right in post #13. The round disc that is pinned and sometimes splined to the focus shaft has a cam that is hidden in the square cutout on the grey plate. It cams that plate down to pinch the rail between itself and extensions of the back standard. This works quite well in the B&J cameras that I've used. With help from that odd spring pressing down against the plate it locks the back standard without shifting focus.
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