The Grand Master That Won't Rekey Cleanly
A property manager brings you a 6-pin Schlage-compatible system for a 24-unit building. The existing grand master (GM) opens all 24 units, a single master (M) opens all units on floors 2 and 3 only, and each unit has its own change key. You are asked to add a new restricted section of 8 units on floor 4 under the same GM without disturbing any existing key. On inspection you find the current GM and M share the same bitting in pin chambers 1 and 2, and the change keys for the 8 new units must reuse an existing keyway. You have a working pinning chart but no documented progression mathematics for the original system. The manager wants the work done in one day with keys cut before you arrive.
1. What is the first technical determination you must make before cutting any new key or pinning any cylinder, and why does it govern the whole job?
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The first determination is whether the existing GM/M/change-key relationships are internally consistent under a single progression rule - i.e., can you reconstruct the two-level (or three-level) hierarchy purely from the existing cuts, or does the system already contain a contradiction (a change key whose cuts would also satisfy the M or GM positions, or two change keys that collide on a chamber they should not share)?
Why it governs everything: if the original system is not a clean progression, then any new section you build to 'match' it will inherit the defect. You would be adding 8 units whose keys may inadvertently open existing units, which is a security failure you cannot detect after the fact without a full audit. Before cutting keys you must map, chamber by chamber, the GM cut, the M cut, and each change cut, and confirm that (a) the GM differs from M only in the chambers the system designates, and (b) each change key differs from M in at least the required number of chambers. If the chart cannot be reconciled, the correct answer is to stop and recommend a documented rekey of the affected section rather than to improvise a parallel progression.
2. The existing GM and M share identical bitting in chambers 1 and 2. How does that constraint shape where you can place the new floor-4 section?
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Because the GM and M are identical in chambers 1 and 2, those two chambers carry no discriminating information between the top two levels. All differentiation between GM and M - and therefore between GM and any subordinate - must live in the remaining chambers (3 through 6). That means the new floor-4 section must be separated from the existing M using only chambers 3-6, and it must still differ from the GM in the chambers the system reserves for GM-vs-M separation.
Practical consequence: your available 'address space' for the new section is narrower than a fresh 6-pin system would give you. You must verify, on paper, that 8 new change keys plus a new sub-master can all be placed in chambers 3-6 without colliding with any existing change key on those same chambers. If the arithmetic does not close, you cannot honestly promise the 8 units fit under the current GM; the options become a deeper cut (more chambers of variation), a separate keyway, or a documented rekey. This is the judgement the exam is testing: recognizing that shared high-order chambers shrink the progression and force an explicit feasibility check before committing.
3. The manager insists on keys cut in advance so the work finishes in one day. What do you do?
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You decline to cut production keys before the pinning chart is verified and a test cylinder is built and proofed. The reasoning: a pre-cut key that is wrong is not a recoverable error - it is either a security hole (opens more than intended) or a service call (opens nothing), and in a 24-unit building either outcome is a liability you created by skipping verification.
A defensible one-day plan: (1) arrive with the reconstructed chart and a single test cylinder pinnings; (2) build and proof one cylinder against GM, M, and change keys before touching the building; (3) once proofed, cut the remaining keys and pin the 8 units in sequence, testing each against its own change key and against M and GM. If the chart cannot be proofed, you convert the day into an audit and give the manager a written scope for the rekey. Communicating that trade-off in advance - one day of verified work versus a rushed job with a hidden master-key exposure - is the professional obligation here.