Along with my new Sargent and Greenleaf 826C that I recently received, I also got this beauty:
It’s a lock from a safety deposit box as used at banks etc – this one is Yale branded. These locks are fitted to the deposit boxes and have two keyways – one for the customer and one for the bank or institution. When the customer needs to access their box, they and a bank representative will both jointly be at the box, and both keys are required to open the lock, ensuring that the bank cannot open the customer’s box by themselves and conversely a customer cannot open anyone else’s box, or even their own without the bank staff present. This ensures higher security and trust in both directions. At least, that’s my understanding!
I believe that the bank key side is the same bitting for all locks at that bank branch (or institution of any kind), whereas the customer side is normally unique for each lock. Because the bank has more to lose from losing one of their keys, and because only one key is owned by the customer, I believe this is why with these kind of locks often the bank side key is missing. In this case, I have the original customer keys and a duplicate bank key.
Going forward, I’ll refer to the customer side (for reference, that’s the left-hand side keyway with the larger, 6 pin key) as the Operator key and the “bank” side (that’s the right hand keyway, which is smaller and takes a 5 pin key) as the Control key – not because that’s the correct terminology (I’m not sure if there *is* a correct terminology?) but because that makes the most sense to me coming from an S&G perspective (although the keys don’t really perform the same job, since in this case BOTH keyways are needed to open the lock rather than one keyway with two directions of operation as per the S&G locks, but I digress). I’m trying to avoid making the assumption that a bank would be the only entity to use these, so if you know of a better term for the two keyways, do let me know!
Moving on then. This lock has a lovely finish:
Even though it’s dirty and worn, it still looks great and you can imagine how shiny a brand new one would look! It seems to utilise a solid brass body and a copper front plate, with a brass cylinder. The main cylinder sticks out quite a way from the body and I assume the body itself would be mounted inside the box, whilst the cylinder with both plugs will stick out through the front of the box. The front of the cylinder has the Yale logo and both keyways side by side – the larger Operator plug on the left and the smaller Control plug on the right. The two grey screws on the top left and bottom right corners are used to disassemble the lock – the front plate with the cylinder comes out forwards from the body and the five-sided body shell is left behind (we’ll get to that later). There are also four large empty screw holes which I assume is where the lock body would be attached to the inside of the deposit box.
Here’s a shot of the operator key:
It appears to be the original Yale key, which is very cool. The front of the key is stamped “YALE Paracentric” and “Yale & Towne MFG.CO. Stamford.Conn.U.S.A.” and the serial number. We can see that this is a 6 pin key, and has an interesting cut-out on the reverse side of the key shaft, about 2/3rds of the way down. We’ll see if we can figure out why during disassembly!
Reverse of the key:
This code seems too short to be a blind code (and I assume that’s what the serial number on the other side is for) so I assume this is an identifier for the bank or institution that it was used. Maybe box number 2817, or room 2, row 8, box 17 or something like that.
Close up of the bitting and that reverse cutout:
Here you can see both original keys:
Here’s the bank/control key, which is on a JMA blank – I assume this was cut to code or to the lock’s bitting after the lock was obtained:
And the back of the key – I assume these letter/number combinations refer to the key profile?
Back to the lock body then. Here’s the back of the lock case:
Side/edge of cylinder:
Now, let’s see how this lock works. As I understand it, there are two types of bicentric locks – dual custody, and shared custody. Both are locks with two keyways, but with dual custody, both keys must be inserted and turned in order to open the lock. With shared custody, either of the two keys can unlock the lock by themselves. This is a dual custody lock.
If we insert and turn just the control key:
We see that nothing happens – the bolt (on the left side) does not retract.
Now let’s try inserting just the operator key:
The key will insert fully, but will not turn – something is blocking it from rotating (I should note that it’s the operator key which actually actuates the lock and retracts the bolt, although unexpectedly the control key does actually interact with the bolt in its own way – it’s not just jamming the operator key closed!):
If we insert both keys, and then turn the control key...
... We can then rotate the operator key, retracting the bolt:
Note that doing so automatically resets the control key to the upright position.
At this time, the bank teller (or other authorised person) will remove their key and walk away, allowing the box owner to retrieve / store their contents in privacy:
When they are done, all that is needed to secure the lock again fully is to rotate the operator key back to the locked position as normal, driving the bolt out – note that once locked, the control key will again be needed to unlock the lock:
So, how does it work? Well, let’s take a look and see if we can figure it out...
First, we have to remove those two flat-head screws from the front plate:
Then (with the aid of a screwdriver to gently pry the front plate off if it doesn’t want to leave!), remove the front plate:
Here is the inside of the lock body:
You can see the bolt unit on the left extending most of the way through the body, and a spring-loaded lever in the top right. That’s all there is to this part!
Here’s the back of the front plate / cylinder:
Two regular cylinders with special tail pieces.
Both parts together:
I will now attempt, as best I can, to describe the operation of this lock – please excuse any mistakes as I’m doing this entirely through trial and error, and learning as I go! I will be using a modified (numbered) version of the above image:
I’ve numbered the parts to make it easier to refer to them. I’ll detail the parts (and any other names I might call them!) below.
1 – Bolt (or Bolt assembly)
2 – Bolt nub
3 – Bolt lever indents (upper and lower)
4 – Bolt lever
5 – Operator cylinder actuator tab
6 – Operator cylinder actuator lower interlock
7 – Control cylinder actuator upper tab
8 – Control cylinder actuator lower interlock
Again – these probably have proper names. Excuse my ignorance!
So, let’s start out by defining what the lock is required to do, and what doesn’t work, and why, before we look at how it works. The lock requirements are that it requires two keys to unlock – more than that, the operator key is not allowed to unlock the bolt without the control key, and the control key is not allowed to unlock the bolt at all. The operator key must return the control key to a removable position once the bolt retracts (so that the staff/supervisor can leave to give the customer privacy), and the customer should be able to lock the box fully without needing the staff member to return.
First then, why can’t the operator key rotate without the control key present? When the front plate is fitted into the body, (5) sits between (2) and the right-hand edge of the bolt (1), where the slope finishes. The odd > share cutout in the edge of that bolt (1) slope is where the right hand edge of (5) (and the continued round right hand edge of the actuator thereafter) fits into the bolt. As bolt (1) is fixed in place, so too the actuator 5 is prevented from moving, and since that’s attached to the plug with screws, the plug and thus the key cannot move either.
As a quick aside, why can’t bolt (1) move? Well, it’s hard to tell in these photos but where the bolt enters the body just to the right of (1), the bolt is actually much thicker inside the body (going all the way down to the bottom of the lock case), so only the bit that is protruding is actually able to fit through the hole in the lock case. In the other direction, nub (2) is “stuck” on (3), which prevents it from moving further into the lock case. This part is core to the locking mechanism.
With that question answered, why can’t the control key open the lock by itself? Well, let’s look at what the control key does. When you rotate it clockwise, (7) rotates anti-clockwise, as does (8). The top point of (7) fits into the chevron ^ shaped cut-out that is (4). As you turn the key, the nub on (7) pushes against (4), lifting the lever (under spring tension provided by the lever spring above the (4) lever) until nub (2) is clear of the upper notch (3) and now lines up with the lower notch (3). Thus, the control key can move the lever out of the way of the nub (2), but it does not and cannot actually interact with the bolt assembly (1) at all – there’s no way for the control cylinder to actuator the bolt.
You may ask “Well, with the control key unlocking the lever, can’t I just push the bolt in from the end?” – Nope, because the actuator tab (5) is still locked between (2) and the right hand edge of the bolt (1), preventing the bolt assembly from moving. If the control cylinder has been unlocked and the correct operator key is in the keyway, you can push the bolt in, since because the operator cylinder is technically “unlocked” (correct key inserted and cleared the shear line, thus it’s able to rotate), pushing on the bolt applies rotational pressure to (5) and thus the cylinder by means of pushing on (2) and the right edge of the bolt assembly, causing it to turn.
Note that you cannot turn the control key anti-clockwise rather than clockwise, because the lower right edge of (7) gets stuck on the left hand edge of (5), as you can see in the labelled picture.
So, now we’ve addressed that – let’s try to discuss how this lock works.
First, you insert the control key and turn it. As you turn the key clockwise, (7) and (8) turn anti-clockwise as seen from the reverse. As (7) turns clockwise / to the right as seen from looking down into the lock case perspective, it pushes on the right hand side of the chevron ^ cutout at the (4) position. The spring lever above (4) provides spring tension as you turn the key, and the lever, pivoting on the rod at the far right side of the lock case (immediately right of where the spring is locked into the lever), rotates upwards. This causes the upper notch (3) in the lever to be lifted clear of nub (2), freeing the way for the bolt (1) to slide back until nub (2) fits into the lower notch of notch (3).
At the same time as you are rotating the control key and causing (7) to do the work, (8) is also rotating towards the upper end of the gap above (6). When fully rotated, point (8) will be entirely filling the gap above (6), like so:
The control key is now “set”, and the lock is ready to receive the operator’s key (which may have already been inserted, but would not have been turnable until this point because (5) was caught between the edge of the bolt (1) and the nub (2), which in turn was caught on the upper bolt lever indent (3)).
Note that with no control key inserted, the operator’s key cannot turn in either direction due to the info in the last paragraph, and even with the control key inserted, the key cannot turn anti-clockwise because the right hand edge of bolt (1) will stop it. Likewise, when the bolt is open you cannot turn the key clockwise any more, as nub (2) is now jammed on the lower indent of lever indent (3).
We now insert the operators key and also turn clockwise. As we do so, (5), trapped between (2) and the edge of the bolt (1) on the other side, exerts pressure on the left-hand edge of nub (2). This converts rotational pressure (from the key) into horizontal/longitudinal pressure. With the lever now lifted and the upper bolt lever indent (3) no longer blocking the path, (5) slides bolt (1) to the right until nub (2) now sits against the left hand edge of the lower lever bolt indent – at this point the exterior portion of bolt (1) is now (almost) fully inserted into the lock body. Here’s a photo of how this looks inside the lock body:
As you can see, the bolt is fully retracted and the nub (2) is now resting against the second (lower) notch/indent in the bolt lever (3).
So at this point, the lock is open. But you’ll remember from earlier that when you turn the op key, the control key returns to the removal-able position for the staff member to take the key away. How does this work? Let’s take a look – it’s one of the main reasons for the interlock functionality on the back of the plug actuators. You may want to refer to the photo from a couple of pictures back, showing the interlocking actuators on the back of the plugs, in the “control unlocked” position.
Like the control plug actuator (7) and (8), whilst the operator plug is turning and (5) is retracting the bolt as previously described, the lower interlock on the control cylinder actuator (6) is also rotating anti-clockwise. As it does so, the edge of the actuator above the gap from (6) (damn, I should have added more numbers!) presses down on the newly-mating (8) edge. As it does do, it rotates the control key actuator back in the clockwise direction, until (5) has rotated to roughly the 12 O’clock position (bolt (1) fully retracted) and the control plug has been rotated back to the 12 O’clock position also, allowing the control key to be removed. Note that the control key cannot be turned back again in this position, as the bottom-right edge of (7) now catches on the rounded edge above (6), as follows:
The control key can now be removed from the lock, and the customer left in privacy. When they are done with the box, it can be re-locked simply by rotating (anti-clockwise) and removing the operator key. Let’s look at how that works.
Note that the control key actuator ((7) and (8)) is already in its “final” locked position. Rotating the operator actuator (5) and (6) does not interact at all with (7) and (8) at this point. On the back of the front plate, rotating the operator key to the lock position simply means that (5) will rotate until it reaches the position shown in the lower photo in the numbered picture, and stop.
Inside the lock body, as (5) rotates left / anti-clockwise, the left-hand edge of (5) pushes on the right hand edge of the bolt (1) cutout (where the > shaped cutout is, at the bottom of the slope). This pushes the bolt (1) back in the left-hand direction, pushing the locking bolt out of the body. Nub (2) also slides along the underside of the lower indent of the lever (3), until it clears the gap for the upper indent. At that time, the lever, being under constant spring pressure from the lever spring, will snap down, returning the nub (2) to sitting in the upper indent of the lever as shown in the upper image from the numbered picture. At this time, the lock has been re-locked and cannot be opened again with just the operator key, even if the key is not removed – because the nub (2) is now once again jammed on the upper indent of lever (3).
Phew! I hope that all made sense – I think this is one of those occasions where a short video would have been quicker and easier to understand, hope hopefully this is of use to someone .
Let’s move on now to stripping the lock cylinders (if possible), and see what pins they hold!
We’ll start by looking at the back of the lock:
That’s an interesting silver tab attached to the copper plate & “body” of the front plate. Surely this is what holds the cylinder on, right? But why is there only one of them?
Hmm, nope, that’s not it. Just a small half-circular metal disk, and the cylinders won’t come out from the main front plate. So, what’s this for? Well, let’s look at where it attaches to the cylinder:
So – it’s embedded in the main cylinder between the pin stacks as you can see. It seems to intersect the keyway itself... Let’s think back to the keys – didn’t they have a weird cut on the back of them?
Yup, that’s what it’s for. The cut-out in the silver disk (see a couple of photos back) creates a gap in the keyway to allow the key to insert normally, but when the key is turned, the plug will rotate and the non-cut-out areas will intersect the keyway. If you weren’t using these correct keys, with the cutout that fits into any portion of the semi-circular disk, the plug would be unable to rotate. An interesting piece of key control!
With that out of the way, it’s time to remove the rear cylinder actuators – one for each plug:
Two simple slotted screws in each:
Back of the plugs:
As I inserted the key and got the lock ready to gut (large cylinder first), I accidentally let the rearmost driver pin pop out. What a strange looking pin! We’ll get to that soon:
Large (operator) plug removed – 6 pins:
Note the cut-outs on the edges around 2/3rds of the way down, where that silver disk intersects with this plug. I never tried, but I assume it’d be impossible to remove this plug without removing that disk first, since it will be embedded into that groove and hold the plug in place.
Key pins removed:
We see that these are all the same kind of pin – no actual security pins as such (in the sense of spools, serrated, etc) but these are almost like very, very finely serrated pins – loads of fine grooves go all the way up each pin, similar to screw threading. Interesting that this is on the key pins, not the drivers.
On the back of the plug with the key inserted, you can see where the cut in the back of the key lines up with the groove in the plug and the disk:
Front plate with the operator cylinder removed:
Note you can just about see the first key pin in the other plug – it looks to be the same type of pin!
Springs and driver pins removed from the operator plug:
Note that the drivers looks *exactly* like the key pins, and the key pins just look like rods that have had their tips sharpened a lot. My theory is that these pins are made from either screw-threaded thin rods, or smooth rods which are then screw-threaded after being made, and are then cut to size and sharpened on the end if they are to become key pins. This is backed up by the fact that some of the pins have a little “nipple” – pinch-off point in the centre of their end where they were crimped to size. This means that both the key pins and driver pins can be “serrated” (and it seems like both pin chambers (plug and housing) are threaded as well, although it’s hard to tell for sure), at the expense of all pins having to be the same “size” – there are no traditional spool, mushroom, etc shapes here.
The smaller, control cylinder (5 pins) was then stripped – here they are next to each other:
Note how, since they both have to be the same length (as they both “start” at the same place in the front of the lock, and as they both have to “end” at the same place for the actuators to work) but the smaller plug is only 5 pins, there is an unusually long gap of “no pins” at the back of the plug.
Front of the cylinder with both plugs removed:
Smaller cylinder pins – exactly the same kind as the larger one:
All the pins laid out – Operator cylinder on the left (6 pins), control on the right (5 pins):
All the lock parts laid out:
It’s time for a clean! In my time-honoured tradition, I soaked the larger parts in GUNK and cleaned off the pins individually using GUNK and WD-40. Took ages and the pins just kept producing black/grey grime on the cloth! I assume the hundreds of tiny threads didn’t help with storing all that c**p, haha. Here’s the parts after cleaning:
If you look at this photo and then the last, you’ll realise that the body is a bit more stripped down now – the bolt assembly and lever spring have been removed. I didn’t realise they could be removed until I was shaking the lock body upside down (after GUNKing) and they started falling out, so I stripped them out and cleaned them properly too.
In the process of re-assembly:
I lubed up the cylinders with Tri-flow and the back of the bolt assembly with Lithium grease to make it slide easier back and forth now. Oddly the lock cylinders seem to “catch” more and have trouble opening sometimes now, after cleaning – maybe the grime was helping the lock function better, haha! I did also flatten off those “moulding marks” on the end of the pins, so I wonder if the added length created by those helped the pins be at the correct height?
What an awesome lock! I loved learning all about how it works and stripping it down – now I just need to find a way to mount it!
Thanks for joining me .