:-)
Yes -- you need to know the offset from the last digit dialed to the extra rotation needed to withdraw the bolt, of course. Pretty much a constant within a single brand of safe and lock.
At least the setting dials (hub rotates within the disc when unlocked by a special key from the inside in the S&G locks) do have 100 different points on the knurling, so you can set them that precisely. It is all down to how tight a fit the projection on the withdrawal lever is to the notches -- and it has to be at least a certain degree of loose, because the lever swings instead of moving in linearly, so there has to be a certain amount of slop.
Of course. "You are not a security expert! We don't have to listen to you." :-)
Indeed so.
:-)
Once you have it open -- you can (if necessary) disassemble the lock and set the combination to what you want. If you have the S&G style of lock, you re-dial the combination which worked to a different index line (about 10 or 15 degrees to the left of the working one), put a special key (extruded square stock with one flange sticking out, a notch to clear the backplate of the lock, and a pilot bearing on the inner end), which goes through square holes in cams on the dials -- now lined up under the hole by the re-dialing on the alternate index line) and turn it CCW to unlock the discs from the hubs. You then dial the *new* combination using the offset index line, turn and remove the key, test several times that the new combination works *before* ever closing the safe drawer or door. And make sure that you can *remember* that combination, or expect to have to go through this again.
If you have an S&G lock apart and no known combination, turn each of the locking cams to loose, stack them back on the spindle, and rotate them by hand to line up with the socket for the end of the setting key, keep something round in there while you put the backplate back on, and then replace the round shaft with the key, dial the new combination, and lock it in as above.
The Mosler security file cabinets had a lock which *had* to be disassembled to change the combination. You pull four screws and remove the works with the backplate. Then remove a C-clip and slide the discs off the spindle. Each one is two part. The hub is splined and snaps into a matching spline in the disc, and molded into the disc is the dial of numbers from 0 to 99. So, you rotate the hub and snap it into the disc to set the combination. Three times -- one for each disk. And make sure that you assemble them in the proper order.
The above about testing that the combination *works* several times before you ever risk closing the drawer applies as above.
That requires memory, which requires a reliable power source, especially to energize the solenoid to lock it against other rotation. (You might as well make it a numeric keypad to enter the combination, but again the need for a reliable power source comes into the game. And what do you make it do if the power fails? Does it lock forever? Does to fail unlocked? Do you have provisions for connecting an external power source if the battery dies? What if someone applies too much power to those connections, frying the circuit? All questions which apply to a lock with memory. :-)
:-)
Actually -- you are now talking about vaults, and usually the wall or the floor or ceiling are typically the weak points in there. Certainly that is how I would have tried to get into the vault at the head office of our division if necessary. (E.g. if they changed the combination and it did not work after the door closed. :-)
Enjoy, DoN.