Spent last night retrofitting a fancy electronic combination lock on a metal door for the first time, and encountered something I don't understand.

The door has previously had another mortise lock, so I assumed it was set up for the American Standard Mortise and this would just be a matter of drilling the additional holes to support the lock body. I was half right; it was ASM and the mortise body it without any trouble. There turned out to be a problem with different knob center and having to enlarge that hole from 3/4" to 1" and shift it upward a bit, but that was expected.

What I didn't expect was a battle drilling the mounting holes. Drill first hole, no problem. Drill second... and first is suddenly partly blocked by an internal piece. I had to continue arguing with that for the remaining four holes above and below the lock body.. If I'd known to expect that, I'd have brought a bunch of dowels or extra drill bits or something to try to stabilize the position of that... but I didn't expect it, and I'm still having trouble explaning it.

Question: Why would there be an apparently mobile sheet-metal inner box within the mortise opening? Is this a normal part of the design of these doors (and if so is it general or manufacturer-specific), or is it something a previous locksmith added to strengthen the door (seems unlikely), or was it something that should have been spot-welded in place but wasn't, or...?

  • Nobody knows, hm? Best thought I've had was that it wss intended as a dúst/insulation shield for the lock mortise, and was supposed to be tack-welded in place but broke free... But that is only a guess.
    – keshlam
    Dec 30, 2015 at 16:00

1 Answer 1


Check with the manufacturer, it may be defective. Usually something like that moving around is for adjustment...i.e. non-mortise locks having different backsets to accommodate pre-drilled doors that may differ. I haven't run across a mortise lock that was adjustable, the door has to adjust to them.

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