Designing a new lock and key

[davidbenjamindix]

I am a designer and woodworker. I am attempting to build a special type of lock and key. All of my locks and keys up to now have been made with wood and neodymium magnets (strong earth magnets). I want to build a multi-piece key that fits into a type of tumbler lock. I'm thinking that the key can have something like 8 pieces that fit together with pins sticking out of each piece. You can rotate each piece to one of four different so the pin is facing up, down, left, or right. When you have each pin lined up in the right position, the key can properly fit into the key hole, and then turned to open the lock.

Or maybe the key has 8 different pieces on a keyrod, where they can all get pulled off and put back in a different order. Each time you reorder the pieces onto the keyrod, the key still fits into the hole, but maybe won't be able to turn until the right order.

This lock is for a cherry and walnut full-size blanket chest. I'm open for ideas and suggestions.

[lockr]

While magnetic locks are certainly not a new concept, I find it intriguing that you have opted to build your own locking mechanism rather than using a traditional cam lock. The obvious concern I would point out is the reliability of the mechanism you're designing; of course this is a low security application (insert pun here about valuable blankets) but it sounds like the chest that you're building isn't something that you'd want to be forced to damage if your locking mechanism malfunctions in some way. Unless of course you have some alternative method of entry (eg removable hingle pins) if this happens.

However, it's a cool idea. I like hearing about folks who are innovative and opt to build something unique rather than just using an off the shelf component. On the other hand, is the novelty of building your own locking mechanism the only reason you're doing it, or is there another reason? I'm saying this only because commerically produced locking mechanisms are probably going to be more reliable than something you fabricate yourself - (Usually; but this is a different discussion). If you don't want to have a typical keyhole marring the look of the front of your chest there are always options (i'm thinking of the type of locks used in safes, which have a neat long key and often a eustachian plate) that would give your application a cool and unique look.

That being said, i'm intrigued by your design. Is there any chance you could draw out your design and post a scan? It would help a lot in understanding what you have in mind.

[cdman]

... of course this is a low security application (insert pun here about valuable blankets) ...

here goes: What if it's a ... security blanket
I'd be interested in seeing a drawing as well. Don't worry about making the drawing look good- just spend 5 minutes on a napkin and then take a pic or scan it.

[davidbenjamindix]

I've used neodymium magnetic locks on all of my previous lockboxes. I use mostly N53 1/2" x 1/8" neodymium disks. They work fantastic, and are very strong. I have used both attractant and repellant locks. Here's a quick drawing of what i'm thinking of. Sorry about the bad penmanship. I did it quick.

[davidbenjamindix]

What I'm really starting to consider again is a push-button mechanical type lock. I've never dissected a simplex push-button, but have been extremely fascinated with them over the last couple of years. I still have a hard time understanding completely how they work. What I would love to do is have someone physically show me how they work (a locksmith or someone tha thas experience with them), so i can design my own for a lockbox/blanket chest. I'd much rather build one of those than this lock I'm working on right now.

[lockr]

Here's a quick drawing of what i'm thinking of. Sorry about the bad penmanship. I did it quick.

Looks good =)

Just to clarify (so i'm understanding this correctly): the key includes not only the dowel but also those pieces sticking up. The magnets are installed into the sides of the pieces. The pieces are of varying height, meaning that the lock is a sort of hybrid magnetic / warded design.

From your original description it sounds as if you intend that the user can rotate the pieces around the shaft of the key to at 0/90/180/270 degrees (i'm guessing if this is the case the the keyway would look like a big "+" symbol)? Or did you simply mean the user could re-arrange the pieces, but they all stay at the same orientation?

I'm assuming you meant the keyshaft would include a groove so the pieces could be removed and replaced in a valid positions, but once there they wouldn't rotate.

Magnets on their own will limit your key differs considerably (although I realize security probably isn't one of your goals, I just can't help thinking about this aspect). 2^8 magnets will only give you 256 possible combinations, so in this case you'll probably want to include a secondary blocking mechanism.

Some ideas:

If you want to stick with a magnetic key tumbler design, how about using a shaped key shaft (eg square) with a row of magnets down each side. This is just a basic idea off the top of my head. A set of spring loaded pins topped with a magnet in various polarities would block plug rotation - all pins would be held below the shearline by the force of the spring. If a magnet of the wrong polarity was introduced it would pull the pin down further; if the correct polarity was used the pin would be pushed above the shearline. With 2^20 magnets (5 magnets per side) you'd have over a million differs, well beyond what most commercial locks boast. Well it wouldn't exactly be a high security lock but a fairly simple design to implement. Just a thought.

Another idea is maybe something similar to the key of the Geminy lock; making a large flat key but with a group of magnets set into it that would align with a mechanism in the chest. If you bore holes from the back side of the chest you could make a lock that requires a certain magnetic pattern to be present to allow a bolt to retract. In theory you could make a mechanism with absolutely no externally visible parts (assuming you used strong neodymium magnet to retract the bolt internally.. but it'd have to be a pretty strong magnet and a very light bolt/spring).

Not entirely sure either of these would be a good design for your application but you asked for ideas, so here's some =)

[davidbenjamindix]

I like both ideas. one of your ideas seems like http://www.lockwiki.com/index.php/MIWA_EC


i am also checking out wafer locks for some ideas.

[lockr]

I like both ideas. one of your ideas seems like http://www.lockwiki.com/index.php/MIWA_EC

You're right, in hindsight it's basically the same design. I should know better, i'm familiar with MIWA locks

The downside to most magnetic locks IMHO is the lack of combinations, due to the binary nature of magnets. The only way to work around this is to include more magnetic pins and/or a secondary blocking mechanism. I still think this is a reasonable design for your application though as it seems to fulfill your requirements (self-manufactured, magnets)..

[davidbenjamindix]

awesome, thank you very much! and if you feel like it, more puns are welcome also.

[davidbenjamindix]

also, how did you calculate how many different combinations there were in your magnetic example? 20^??? I never studied probabilites or odds so I have no idea.

[lockr]

awesome, thank you very much! and if you feel like it, more puns are welcome also.

You're welcome! Hopefully my input will help out. And maybe some others will chip in with their ideas too =) Your project sounds interesting and I really like to hear about what cool ideas people come up with. When you finish your chest and lock, please consider sharing some pics and info on your locking mechanism.

also, how did you calculate how many different combinations there were in your magnetic example? 20^??? I never studied probabilites or odds so I have no idea.

There are 2 magnetic states, and if there's 20 pins then 2^20 = 1,048,576 possible combinations.

You can calculate the possible differs for regular pin tumbler locks this way too; say for example a lock like a Schalge with 9 possible pin heights and 6 pins, there would be 9^6 or 9x9x9x9x9x9 = 531,441 possible combinations.