Help with designing a unique low-tech door locking system

[Rhydo]

Hi!

I recently built a small 555 based monostable password protection circuit. I designed it so that upon pressing the right keys the monostable goes on for 15 seconds. I can get a small geared motor running for this period but I' am at a loss at designing a suitable lock with it to get a small door locked (once its been closed).

Can anyone help me with some ideas about how to get about building this lock which would use a motor based lock mechanism to lock the door within 10-15 seconds? I can change the timing to as low as 1 second but I' am hoping to get this working with what I have designed.

Thankyou in advance! Any ideas would be much appreciated!

 

[Danger]

Hi, Rhydo;
I might be able to help a bit. While I love to design mechanical things with no regard as to the field of use, I am also a retired locksmith.
To start with, please supply at least minimal specifications as to the dimensions and material of both the door and the surrounding framework. Also the approximate security level needed (ie: are you storing gold bullion or just some ancestral recipes?) It might seem picky of me, but it's critical to the design parameters. Is it on a box, a wall, a floor, a chastity belt...?

 

[Rhydo]

The door actually belongs to a cupboard. I thought building a password encrypted circuit might have been the tricky bit. But I cannot find any information on how to build a homemade lock. And the security need not be high tech! Just enough to show the working of the circuit and yes...deter anyone from thinking that they can force it open without dismantling the whole thing.

My circuit supplies about 9 volts for about 10-15 seconds. I want to lock my two door wooden cupboard (there has to be a single word to explain this!) i.e it has 2 hinges and the doors come together in the middle.

The dimensions of the cupboard are about 5feet high* 3feet length* 2feet thick(thickness shouldn't matter I suppose). I was hoping to use something akin to a solenoid locking system but its hard to find a solenoid (working off a 9volt battery) producing enough magnetism to deter anyone from trying to force the door open.
I know that even a couple of 1.5 volt t.v remote batteries can give enough juice as electromagnets to lift a whole car, courtesy Discovery channel.

We have about 10 seconds of 9 volts supply to play with. I hope the final design won't be very time sensitive i.e 10+-3 seconds.

 

[Danger]

Okay, the design is easy. I've drawn it up in Inkscape. The problem is that I have to jump through more hoops than you can imagine in order to post it. It's going to take a while.
Meanwhile, I'll try to just describe it in words.
The one that I prefer is a simple sliding bolt driven by a rack-and-pinion from the motor. Since you have double doors, I would mount it on the inside of one, rather than on the frame. The bolt should pass through 2 "staples" on the mounted door and 2 more on the other. That will give maximum strength. As an alternative, you could use a slightly different gearing system to actuate a swinging bolt, like a railroad crossing arm. Once again, I would mount it on one of the doors and use 2 staples on each.
As added security, since cupboards usually have external hinges, I would modify the screws. Use Robertson heads (or Phillips if you absolutely have to, but they suck) rather than slotted ones. Obtain some lead (wire, solder, or pellets from an air gun), and hammer it into the openings of the screws to prevent the insertion of a screwdriver. If you have to remove it yourself, it can be pried out with a lot of determination or even melted out. For a casual snooper, though, it's a serious deterrent. I used to use that on things like window bars when I was in the business.

 

[Rhydo]

That actually does sound like a darn good idea! You really are the first person I have had the opportunity to talk to who has any idea what he is talking about when it comes to solving my problem. I have to confess that I didn't understand some of the technicalities that you mentioned, but I can imagine something akin to what you said actually working. Now I need to find someplace where I can get some gears. Also I would have to calculate the length of the bolt required w.r.t the rpm of the motor and the time for which it stays on. Then there is the issue of making it run in an identical reverse motion to get the door open (that can be managed with an spdt swith so I' am not really bothered about reopening), but the availability of gears in and around my locality might be a serious issue.

 

[Danger]

My favourite method of obtaining gears is to collect scrapped VCRs, typewriters, kitchen appliances, and toys. They also provide switches, motors, cams, springs, screws, and other neat stuff, and they're free.
Please tell me which parts of my post you had trouble understanding, and I'll try to explain them better. Meanwhile, I'm still trying to figure out a way to post my diagram.

edit: By the bye, just choose the bolt length according to the size of the doors. Your gear ratios will determine how long it takes to open and close.

2nd edit: I don't know how compatible this will be with your timing circuit, but I always put "limit switches" on things like this so that the motor can't try to provide movement beyond the physical limitations of the mechanism.

 

[Rhydo]

Oh man! LIMIT SWITCHES! I was beginning to wonder why something like that hadn't been invented yet! I didn't even see these things being mentioned other places I looked into.
I'll try and salvage the things that you mentioned. The bold that you spoke of...is it a different entity or can I get a rack to slide into a "staple" using the rotation of the pinion wheel through the motor? I' am sorry if I sound dumb (please be patient) but I didn't get the idea about a 'bolt' when the rack can me made to do the same function with a rotating gear.
Also you could just mail the drawing to me at rhydo19@yahoo.com(would save the both of us a lot of time and effort :)

 

[Danger]

Also you could just mail the drawing to me at rhydo19@yahoo.com(would save the both of us a lot of time and effort :)

I'm not very computer savvy, and so don't actually know how to do that. I'll maybe give it a shot, but I've got a handle on the problem. I had to clear a path to the desk where my old G3's are set up and fire up Illustrator 10. Right now, I'm redrawing the thing, but it's been so long since I've used that program that I'm having to relearn it. From there, I can filter it through Photoshop to produce a file format that ImageShack will accept.
You are essentially correct about the rack being able to serve as the bolt, but there are some complications. The bolt should be quite strong, which includes significant thickness (at least 3/8"). Normally, a rack should be more or less the same thickness as the pinion. Also, there's the possibility of the rack's teeth catching on the staples while sliding through them. For those reasons, I would just attach the bolt to the end of the rack with a pin or something. The bolt and rack could be machined out of a single piece of stock, but I have the impression that such an endeavour is beyond your means for now.

 

[Rhydo]

but I have the impression that such an endeavour is beyond your means for now.

You are right...I have been looking around for a rack and pinion assembly but am yet to fing one. Hopefully I'll be able to salvage one from somewher soon. Machining stuff is beyond question as of now. Your illustration would be helpfull to a large extent.
Is there any other simpler way to build a lock from stuff lying around at home?
I just need to show that the concept works in principle so I can take a lot of artistic liberty. Maybe something that would break if the door is forced open so as to dissuade anyone from trying to open it, lest they have to clean up whatever it is that the lock spews out upon damage?
Does that make any sense? :)

 

[Danger]

You are right...I have been looking around for a rack and pinion assembly but am yet to fing one.

There's usually one in the ejection mechanism of a front-loading VCR. The rack might actually be part of the cradle structure, though, and thus need to be chopped out with a hacksaw.
I don't really see the point of just making a mess instead of keeping someone out, but it can certainly be done. I would recommend "glitter", like they glue on X-mas cards, as the active ingredient. If you've ever tried to clean that stuff up, you'll know why. It could be dispersed by something as simple as popping a balloon full of it or putting a cup of it on the arm of a mousetrap. Be aware, though, that it could cause serious eye damage to your victim. The same could be said about almost anything airborne.
As for an actual lock... if you just want a proof-of-concept device without regard to strength, you could always simply carve the parts out of wood. That's what most of the gears in Leonardo Da Vinci's inventions were made from. They won't be precise or smooth in operation, but they'll work.
I'm somewhat ill and very tired right now, but I'll get back to the drawing tomorrow.

 

[Danger]

Well, this is both irritating and embarrassing. For some unknown reason, there's some screw-up with both of my G3's and the internet, despite that both are feeding through the same modem/router as this MacBook. ImageShack wouldn't let me upload from Photoshop, claiming that I'm at my 500-picture limit (I have 141). I couldn't even e-mail the file to myself to open on this machine. Out of desperation, I took a picture of the Illustrator 10 screen with my Blackberry, bluetoothed it to the MacBook, and uploaded it to ImageShack as a jpeg. The drawing itself is very rudimentary, just to give you a better idea of what I meant, and I have to apologize for the picture quality. It's never easy to get a photo of a CRT screen, particularly under adverse lighting conditions.
Anyhow, here it is.

http://[PLAIN]http://img84.imageshack.us/img84/5885/cupboardlock.jpg
Shot at 2012-04-30

 

[Danger]

Hmmm... too late to edit the previous post to add a comment.
Just in case there is any question about it, the drawing is not even vaguely to scale and doesn't represent the fact that the parts will be in a 3-dimensional relationship. The gears and motor were drawn oversize in order to show up in the screen image, and I left out all of the electrical bits.
Now that I've figured out the Blackberry trick, I'll do up a new, proper set of drawings in Inkscape on this machine and put them up on ImageShack. Since this has an LC screen, the photo should be better.
Come to think of it, maybe a screenshot will be in a format that I can upload. That would certainly simplify things.

 

[Rhydo]

That is incredible! Thankyou so much for putting in so much effort to solve my problem!
I think I might have something that will work based on your design! And don't worry about having missed out on something in your illustration(which is actually not bad by the way!), you have seeded the idea in my mind such that its now clear what I have to do.
I' am trying to get alteat a rudimentary system running based on your design.
Hopefully I'll have something better to report by tommorow!
Thankx a lot for being so consistent! It would be nice to have teachers like you around!

 

[Danger]

Thankyou so much for putting in so much effort to solve my problem!

I believe that I should be thanking you for giving me something to do. My terminal lung disease means that I pretty much can't leave the house. My entire life, therefore, is spent watching TV (mostly reruns), playing Adventure Quest, drinking a lot of beer and Scotch, and snooping about on PF. I try to eat once or twice a day, but it's not a priority. Someone does me a tremendous favour by offering a technological challenge, so that I might exercise my limited intellect to some extent. I thoroughly enjoyed this project.
Since you have something in mind, I will forgo doing any more drawings unless you request them.

It would be nice to have teachers like you around!

I don't think that your education would have been well-served by having a teacher who never finished high-school.
(If you want pool lessons, though... )

 

[Rhydo]

I don't think that your education would have been well-served by having a teacher who never finished high-school.
(If you want pool lessons, though... )

Einstein once said, true education is what you remember after your education is over. Your qualifications don't matter (atleast to me), its your knowledge that is impressive. Had there been more teachers like you around, many of us would not be dumbfounded with basic engineering on a practical level.
Anyway, I did manage to acquire a couple of gears yesterday but the rack still remains elusive! Since you are a retired lock smith, riddle me this- how do they make unique keys for locks from a massproduction stand point? I mean every key is unique so they couldn't just use a die and stamp keys out onto the conveyor belt can they? And more importantly...you must have picked atleastone in your life time :) Who better to ask about lockpicking than the masters themselves-the lock smiths!

I really hope from the bottom of my heart that you get well soon!

 

[Danger]

I really hope from the bottom of my heart that you get well soon!

I'm afraid that there's no possibility of that, but the sentiment is very much appreciated. It's COPD. I was supposed to have been dead about 3 years ago, and actually was for a brief period a year ago, but I'm too damned stubborn to leave what I consider to be my planet. (I could improve with a lung transplant, but I'm not going to apply for one.)
As for the key issue... there are hundreds of manufacturers, so the specific techniques vary. In essence, though, the key blanks (usually 2 per lock) are assigned a code by the control computer. That code is stamped onto the head (eg: 14374 for a Weiser key), and the same code is entered into a grinding machine similar to the cutter in your local hardware store but not manually operated. The grinder cuts the appropriate profile into the blades of the blanks. Before, after, or coincidental with that, the corresponding lengths of bottom pins are loaded into the core of the lock that those keys are made for. (A deep cut gets a long pin, a shallow one gets a short pin, etc..) If it's a brand that uses proportional driver pins, then those are also calibrated to the code.
It is also a misconception that all keys are unique. That is not even close to possible. Factories repeat their codes on a regular basis. They do try to ensure, however, that duplicates are not shipped to the same geographical market. Identical units will be shipped to Los Angeles, Toronto, London, New York, and so on simultaneously. In fact, due to the sheer population issue of New York and London, there are probably at least 1,000 locks in each that were factory-shipped with the same code. There are some brands such as Weiser, Amerock, and Kwikset that have only one broaching profile, while Schlage has about a dozen. For instance, you could have two Schlages next door to each other with the same code, but the key for one will not physically fit into the other because the grooves along the sides don't match. There is also the fact that a significant percentage of those factory units are changed in application. One of the largest parts of my business was recoding locks in the case of someone buying a new house or losing a key that someone might find and use for nefarious ends, and masterkeying aparment buildings.
I have no idea as to how many thousands of locks I've picked since I opened my company in '79. Some take less than 2 seconds, but I've spent as long as an hour. If I haven't gotten it by then, I give up and use more drastic methods to open it (drills, grinders, crowbars... I opened one with a .44 magnum once, but it isn't considered a proper professional technique. :uhh:)
This brings up something that irritates me to some extent. You can get all information needed to pick a lock on the internet. When I went through locksmithing college, before the net existed, I had to swear an oath to never wrongfully open a lock (ie: for other than the owner) or instruct anyone as to how to open one. I'm not even allowed to let anyone see my picks, lest they make their own and figure out how to use them. If I violate that oath, I go to prison for 14 years. If I were to break into something for my own gain, it would be 21 years (14 for violation of oath and 7 for break-and-enter, consecutive). No chance of parole in either case. That oath is a lifelong thing, so even if an unlicensed person who knows how to pick asks me about it, I can't discuss it.

 

[Rhydo]

Thankyou for telling me so much! I learn something new everytime you post a reply! I'am sorry for asking you about lock picking, I really don't have anything illegal in mind, I'am just too curious for my own good sometimes :) Thankyou for still giving me a lot of information without actualy breaking your oath ;) I completely agree with you, an Oath should always be a sacred thing, nice to know that there are still a few people who have unwavering integrity and morals! I had a feeling that not all keys could be made unique...that would be an industrial nightmare!
I'am so sorry about the COPD, I have no idea what you are going through but when the worse has come to pass things can only get better (thats what mom says). So things can only get better for you now. But I salute your will, sir.
Would love to hear the one about why you had to open a lock with a .44 magnum. Not many people have such a tale to tell and not be on the 'most wanted' list! :D I hope this won't interfere with your oath!

 

[Danger]

when the worse has come to pass things can only get better (thats what mom says)

I hope that she isn't referring to your birth... :uhh:
Sorry, pal... I still have to try to be funny once in a while.
Don't apologize for asking about picking. I actually first got into doing it when I was still in school. I had a couple of favourite TV shows, and one of them was "It Takes a Thief" with Robert Wagner and Malachi Throne. At about the same time, Reader's Digest had an article about a jewel thief who was pseudonymed "Armand" by the writer. Both piqued my interest, and led me to experiment.
My mother was quite proud that I got home from school one day when my parents were away, popped the lock, baked myself a cake for lunch, relocked the door, and was off at my friend's house when they returned. (That was before I had my own key.)
The .44 mag incident was a couple of years after that, long before I ever became a locksmith or even considered becoming one. I had forgotten the code for one of the dial-combination Dudley padlocks that I had used on my school locker after I had it at home. Since I wanted to see what was inside, and liked to dial in my Super Blackhawk whenever possible, I set the thing up in my back yard and took a whack at it. I can only assume that I succeeded in opening it, because I never found it. (Luckily, none of my neighbours did either.)
I must point out here that the previous description that I gave of lock-and-key manufacture was severely limited to only the simplest type of pin-tumbler units. There are dozens of other systems, ranging from the old bit-key (what some call "skeleton key") style up to stuff like Medeco biaxial locks (for which I was factory trained), Abloys (my fave), magnetic stuff, dimples which in my early years were produced by only Dom ix, chip keys as used in automotive ignitions... There is an incredible array, and most of the high-security stuff such as the Medecos, Abloys, etc. are ridiculously difficult (essentially impossible) to pick or even force open. When I had my Medeco factory training, for instance, there were 3 people in the world who could, using 6 picks simultaneously, open one out of every 10,000 Medeco locks. They also have armour plate steel inserts at all of the drill points and over the screws. I don't know what they're up to these days, but when I was in the biz their best was the Ultra 700. It's a 1 kg vise with a biaxial lock in it, which replaces part of the door. It throws a 1.5 inch bolt, about the size of a Zippo lighter, into the frame. When I dealt with them, they cost about $250.00, and were well worth it. (The top Weiser model was about $30.00.)
So, about the picking... it is in no way a violation of my oath to suggest that you check out "How Stuff Works" (that's not the actual address, but close to it; just Google it). They show everything from how to make Jell-O to how a neutron bomb works.
With regard to my joke about your mom... my mother slept through my birth. When she finally woke up, the doctor handed me to her. She looked at me, looked at the doctor, looked back at me, looked back at the doctor, and said "What the hell am I supposed to do with that?" That pretty much defined our relationship, and my general attitude in life.

 

[Rhydo]

:D I walked right into it didn't I?! Anyway I never really got to know what my mom said when I was born so your joke could well be true! What surprises me is not that you picked your own lock while at school but that you actually baked a cake for yourself! As always I have a ton of stuff to lookup in the internet after having read your post. And trust me I did look up 'How stuff works' and I have googled it as well...not to mention 'youtube', but I still had to ask you. I havn't really been picking locks but the knowledge might come in handy someday!
Your mom seems like a nice lady! ;)

 

[Rhydo]

HEY!

I finally managed to build a decent door locking system..
Well its not good for 'protection' purposes :P but at-least I managed to show that the concept can be built cheaply at home!

Thank you so much for your help! I hope you are proud!

Here's the youtube link for the video I made-