masterkey systems

[crasher]

i am quite new to locksmithing & am struggling to get my head round masterkeying.
can anyone recommend good reference books, downloads, tutorials etc on the subject?
I understand the principle but what are the limitations?, how many locks can 1 master undo? likewise how many different keys can be used to undo 1 particular lock?
thanking you in advance...CRASHER

[Raccoon]

There are so many different ways to make a master key system, and the limits are too wide and specific to the lock itself.

The MIT Guide to Lockpicking touches on master keying. That's a good start.

[burchlockkey]

http://www.aerolock.com/

These folks have a small booklet on Master Keying Systems. It is basic but that is all you need since each lock brand has its own specific mastering ticks.

[Raccoon]

Some basic rules when creating a master key system. These are not hard-fast rules; they are my opinion, and everyone has their own reasons for doing things differently.

1. Your first cut/pin shouldn't go deeper than half-way. So if your lock takes 0-9 pins, your first cut/pin shouldn't go deeper than 5. This saves wear on your locks, pins and keys. This seems to be commonly agreed upon.

2. Your progression should be in steps of 2. This prevents your system from using #1 master wafers which could jam up a lock by flipping on its side or slipping between the sheer line. So, if your master key is cut 5-3-6-8-2, then all your keys will be "odd-odd-even-even-even" and you should only have to buy master wafer sizes #2 #4 #6 and #8. If you want to go in steps of 3, the odd/even rule wont apply, but you'll only need wafers #3, #6, and maybe #9. This can be quite cost effective, but again, may not be suitable for various systems (especially pre-existing systems you add onto).

3. Use master wafers in as few chambers as possible. If you have only a dozen doors to key, you should only need to have 2 chambers containing master wafers. It would be really pointless if your master key has a '5' cut where all your change keys have a '3' cut, as that means every lock has a useless #2 wafer in that chamber, which makes the lock easier to pick, and increases the chances of random keys or cross keys operating that lock.

4. Avoide the fast-and-easy system of taking 1 arbitrary master key, and making it work in every lock with arbitrary change keys. This is a common method used by lazy locksmiths, which invloves putting master wafers in every chamber so that the arbitrary master works in every lock. As stated in rule 3, you want as few chambers containing master wafers as possible. This cheap method of master keying increases the chances that a neighbor's key will operate any number of locks in a complex due to cross keying. If every pin chamber has a master wafer, with 5 chambers, that means 32 keys can theoretically open the lock. Odds are great that someone's random key will operate that lock. (My apartment key opens at least 2 of my neighbor's locks, and theirs opens mine because of this).

5. If you've created a system from scratch, you shouldn't run into any cross keying. But if you are expanding on an existing system, be sure none of your new change keys match any existing change keys or possible phantom keys (theoretical keys that match parts of existing change keys and parts of existing master keys, that when combined, can open random sections of locks/doors, even an entire hallway). Again, a lock with 5 chambers containing a master wafer can be operated by 32 keys. Even if only 1 master and 1 change key should open it, there are 30 other keys that COULD.

That's all for now. I hope you figure it out.

[supersteph]

i did a quick google search to find any books on "master key systems," and while i didn't find anything relevant - i did find something interesting:

apparently, there is a book called "the master key," which is like a disciplined school of thinking (?) that allegedly helped bill gates get rich.

so if your type of master keying doesn't work out for you, maybe that could be a nice alternative best of luck!

[grim]

2. Your progression should be in steps of 2. This prevents your system from using #1 master wafers which could jam up a lock by flipping on its side or slipping between the sheer line.

i wholeheartedly agree with this one! (not to say i don't agree with the other points presented)

this is particularly bad on arrow cylinders. ALWAYS ALWAYS ALWAYS avoid single-stepping the master/change bittings! this has enough potential to cause serious enough problems down te line that you'll never want to do this again once you've had to deal with the fallout.

[xequar]

Another little thing that IMO is worth heeding...

When I create the Master for the system, I usually try to make sure that at least one of the Master cuts is higher than any Change key cut. For example, you could do a Master with 3140385, and if using a 2-step progression (which is a really really reeeaalllyyy good idea...), then no Change key could ever be filed into a Master because all Change key cuts in positions two and four would be lower than the Master cuts.

Also, Raccoon, for your bullet point number 1, when you say...

1. Your first cut/pin shouldn't go deeper than half-way. So if your lock takes 0-9 pins, your first cut/pin shouldn't go deeper than 5. This saves wear on your locks, pins and keys. This seems to be commonly agreed upon.

...are you referring to the cut at the tip of the key, or at the bow, and is this for all keys system-wide, or for the Master? Honestly, I'd never heard this tidbit before, but it certainly could be useful.

[Raccoon]

Another little thing that IMO is worth heeding...

When I create the Master for the system, I usually try to make sure that at least one of the Master cuts is higher than any Change key cut. For example, you could do a Master with 3140385, and if using a 2-step progression (which is a really really reeeaalllyyy good idea...), then no Change key could ever be filed into a Master because all Change key cuts in positions two and four would be lower than the Master cuts.

Also, Raccoon, for your bullet point number 1, when you say...

1. Your first cut/pin shouldn't go deeper than half-way. So if your lock takes 0-9 pins, your first cut/pin shouldn't go deeper than 5. This saves wear on your locks, pins and keys. This seems to be commonly agreed upon.

...are you referring to the cut at the tip of the key, or at the bow, and is this for all keys system-wide, or for the Master? Honestly, I'd never heard this tidbit before, but it certainly could be useful.

You know what, I was just talking to Zeke about your point about at least 1 chamber being shallower than the rest. We were disputing why the locksmith in the other thread would have cut such ugly masters, and it was probably because /remembered something his training about filing and shallow cuts, so better to be safe and make them all shallow/.

But yes, I agree that it should never be possible to file your change keys down to create a master. This only really matters for institutions that use restricted keyways, as anyone can obtain common key blanks for filing or impressioning, but restricted keys you're stuck with what key you've got. In a good system with rotating constants, ie, different chambers containing master wafers in different subsections of doors (even with submasters), you can simply discard any key codes that can be filed down. Most software will do this for you.

As far as the first pin being no deeper than half; this is referring to the pin closest to the shoulder. (In fact, many people seem to discard any tip-to-shoulder code spec by the manuf., and simply go with shoulder-to-tip for all keying. Shoulder-to-tip is the favored standard.)

I can't explain the physical properties of why a deep cut for the 1st pin will wear down the lock faster. As best as I can tell, this is due to the amount of movement that pin gets. Consider that the 1st pin gets twice as much activity as the 2nd pin, and the 2nd pin twice as much activity as the third... so that in all, the 1st pin touches the key 16 times more than the 5th pin, and 32 times more than the 6th pin.

I speculate if the first pin is especially low, it will spend most of its time above the sheer line (due to law of uniformity of random distribution, half of all random numbers fall below the mid point) because the bittings that belong to the 2nd-5th pins will also pass the 1st pin, pushing it above the sheer. This combined with the pulling and pushing force of the key, will cause the leverage of the 1st pin above the sheer to start hollowing out the chamber in an area important to the lock. Consider that longer pins (for deeper cuts) also provide more leverage (like a long rod) against the fulcrum (the sheer line). This natural wear is best kept below the sheer line, and best reduced with a shorter pin. Since the 1st pin sees the most activity, it's worth paying attention to.

The reason I speculate this is simple. Several quality lock designs incorporate a ball bearing beneath the 1st pin to reduce this sort of leverage and wear. I've even heard of after market ball bearings to fit most standard locks, though I've never encountered either.

Again, all on-the-fly speculation.