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To me it seems entirely reasonable for the hole of a lock to be in the door and the "tongue" of the lock to be in the frame. Is there a reason we usually do it only one way?

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    Wooden door frames usually thicker than a door. Might have almost an inch of wood to hold the hole in place on a frame, but maybe a 1/4 or if lucky 1/2 inch of wood in a door. Need two kicks with a frame, only half a kick with a door.
    – crip659
    Commented Nov 22, 2022 at 0:02
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    You would also keep running into the tongue as you went past the frame. The door is movable. so you walk around it. and normally avoid the tongue. Commented Nov 22, 2022 at 0:12
  • ah wait i see why its a security precaution ill draw a photo Commented Nov 22, 2022 at 0:17
  • strange question, how would the tongue move if it is in door frame
    – Traveler
    Commented Nov 22, 2022 at 0:20
  • @Ruskes You know those electronic door locks that use an electric strike? In those, the strike swivels to release a fixed tongue. I'm imagining a similar mechanism, flipped over with the strike on the door side.
    – user71659
    Commented Nov 23, 2022 at 1:30

6 Answers 6

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The doorknob is attached to the door. This allows someone to twist the knob to retract the "bolt" and then, as a part of a continuing motion, pull on the knob to open the door.

It's hard to envision a scheme where the "bolt" could be tied to the frame while still allowing the door to be opened with one hand.

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    I think every other possible reason could easily be engineered away (standard placement of door in a frame for example would solve depth of door frame), but this is the most logical. Having the handle on the frame requires two hands to operate or multiple separate operations. Commented Nov 22, 2022 at 0:57
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    +1 but this doesn't directly cover many key locks, especially mortice locks. However indirectly it still does (rim locks where you can turn the key then push the door in one movement, mortice locks - to match everything else)
    – Chris H
    Commented Nov 22, 2022 at 10:31
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    I can imagine a conventional knob or handle still being on the door (it just pushes the latch into the jamb), but I’m not sure there’s any benefit to increasing the complexity. (And massively increasing complexity if the door is supposed to lock or deadbolt.) Commented Nov 22, 2022 at 13:31
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    @AloysiusDefenestrate and complexity in matters of security is often where vulnerabilities creep in
    – Chris H
    Commented Nov 22, 2022 at 15:35
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Setting the (several) other problems aside, a bolt sticking out of the door frame is a hazard. Not only can people get injured running into it, but loose clothing can get caught on it. Doors are chokepoints for emergency egress and are designed to keep out of the way when open so that the entire passage can be used for egress by panicking, distracted people. The door frame hoisting people by their own beltloops doesn't comply with this design.

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    I can attest to this. My home has some old-timey-style latches where the catch sticks out from the door frame. I've torn clothes on it and even hurt myself a couple of times on them. I would love to replace them but my SO likes the look of them.
    – JimmyJames
    Commented Nov 22, 2022 at 16:22
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    even as it is, I routinely get my belt-loops caught on strike plates because they happen to be at the exact same height. I am very thankful that there isn't an even bigger obstacle at that height
    – Steve Cox
    Commented Nov 23, 2022 at 17:35
  • It's possible to have a projection from a door or gate interact with a recessed object attached to a stationary frame. This is common with gates.
    – supercat
    Commented Nov 23, 2022 at 18:33
  • I have doors with locks where the tongues are in the door, and they don't stick out from the door when unlocked. Mortice locks being the main example: stick out when locked, not when unlocked. So why does the tongue of a lock have to stick out from the door frame? Just don't use a Yale lock, that sticks out whether locked or unlocked, and only briefly retracts while you're actually opening the door :-) Commented Nov 24, 2022 at 11:16
  • Which leads me to suspect that the issue isn't that the lock needs to be in the door, it's that the spring-loaded latch (not sure if that's the right technical term, but I'll use it) needs to be in the door. Then, combining the lock and the latch into a single unit is an obvious move, but strictly speaking not an essential one. Commented Nov 24, 2022 at 11:19
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Doors are pretty standard so the locks and keys can be universal with minimum adjustments. Door frames, however, are not standard. Look at the variety of exterior door frames. The thickness of the frames vary greatly, some are brick, fancy stonework, siding, decorator trim and molding, etc. meaning the locks would almost have to be custom made. Plus, the installation of the locks and keys would be much more involved drilling through bricks, etc.

Also, the strength of the frame for holding the bolt would be greater than the strength of the door holding the bolt.

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There are sound reasons, some of which have been mentioned already, but don't neglect the role of convention - if we all do things the same way round, fewer different designs are needed, and there's no real benefit to putting the lock in the frame. There often isn't much frame before you get to the next bit of wall or similar, while the door is always going to be big enough to walk through and therefore have enough space to fit the lock. That said I have come across largely-glazed front doors with very limited space for locks. Upgrading the lock for greater security was challenging.

One modern reason that hasn't been mentioned is multi-point locking systems, where the lock mechanism in the door doesn't just lock a single tongue, but (on turning the key) engages bolts or hooks at several points on the door (usually at the top and bottom of the non-hinge side, plus 1-3 points on that side). This provides far greater mechanical strength than a single point lock.

An interesting comparison comes from electronic door locks, where there's a need to get wires to the part controlled by the security system. These are often combined with key overrides in the form of conventional locks, and then it's the striker plate on the frame that's wired. Electric strike with monitoring contact

Reinraum, CC0, via Wikimedia Commons

This deals with issues like the tongue of the lock snagging on people walking through the door (mentioned in the comments), and means it's compatible with existing locks. At the same time it means no need for wires to be hinged.

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Robustness by outside impact. Forcibly kicking open (in case of hurricane by wind) a locked door is much more difficult when the tongue is inside a rigid bulky wall embedded frame than when the tongue is in the flimsy movable plank of the door edge.

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Wood door. Might be a piece wood inside the door knob mechanism. Could also be wet. Wood swells when it gets soaked and wet.

Metal door the mechanism may just need a little cleaning and silicon spray lube. Safe to use on electric controlled doors. Just make sure power is off. The propellant is flammable..

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    I think you're answering a different question than the one that was asked. They wanted to know why the lock is installed in the door and the strike in the frame; you've answered about why the lock mechanism may be getting stuck.
    – keshlam
    Commented Nov 24, 2022 at 18:43

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