Prepare for the BHI Diploma in Practical Horology by organising practice around three connected skill areas — advanced watch service, advanced clock service, and fabrication — and by training the decision-making that links them: observe, measure, choose an intervention proportionate to the fault, and document the reasoning. Check administrative details such as format and entry requirements directly with the BHI at bhi.co.uk, since this guide teaches the craft content rather than exam logistics.
Choosing the right intervention level before you touch the lathe
Advanced practical horology asks you to match the intervention to the fault: routine service, targeted repair, or restoration-level work. Train this as a decision you justify with observations, not a default sequence.
A routine service means stripping, cleaning, checking, lubricating, and adjusting — appropriate when the movement is complete, unworn, and performing within its normal envelope. A targeted repair adds a specific corrective operation, such as a bush or a new mainspring, when one component limits performance. Restoration-level work — replacing major parts, remaking missing components, or re-finishing — changes or recreates material and should be reserved for cases where repair cannot recover correct function.
Build the decision habit deliberately. Before starting any practice movement, write three lines: the observed symptoms, the measurements or inspections that support them, and the chosen intervention with its justification. During the job, note any finding that contradicts your plan, and record what you changed. Reviewing these notes across several movements teaches you where your judgements were proportionate and where you over- or under-treated — a self-critique skill that transfers directly to any assessed practical bench work.
- Service: complete movement, no excessive wear, performance inside normal limits.
- Repair: one identifiable fault requiring a specific corrective operation.
- Restore: missing, badly damaged, or heavily altered parts that must be remade or re-finished.
Bushing a worn clock plate without wrecking the depthing
Bushing corrects plate-hole wear while preserving the original pivot. The difficulty is centring the new hole and re-establishing correct depthing and side-shake after fitting the bush.
In a typical anchored or deadbeat clock movement, years of running wear an elongated, off-round hole in the brass plate where a hardened steel pivot turns. The accepted correction is to drive out the worn material and fit a brass bush, then re-ream the bush to suit the pivot. The craft-specific traps are centring and depth: the bushing tool must locate on the true centre of the original hole, and the bush must be finished so that escape wheel depth, lock, and drop are restored to their correct relationship with the pallets.
Worked scenario — worn escape arbor hole: A candidate notices side-shake and a rough tick, fits a bush, but does not properly centre the pilot hole; the re-reamed bore sits slightly off, throwing the escape wheel deep into the pallets on one side. The ticking is uneven and the lock is excessive on one pallet. The better decision is to mark and verify the centre carefully before drilling, then after fitting, check drop and lock at each pallet stone individually and adjust until they are equal and correct. Why it matters: an off-centre bush silently converts a wear problem into an escapement geometry problem that is harder to trace than the original fault.
| Observation | First-line intervention | Escalate when | Risk if chosen wrongly |
|---|---|---|---|
| Slight hole wear, pivot sound | Re-ream or polish pivot; close hole lightly | Wear returns quickly after fitting | Turning a good pivot down wastes original material |
| Marked oval or elongated hole | Bush the plate, re-ream to pivot size | Plate is cracked or badly distorted around the hole | An off-centre bush ruins depthing |
| Pivot itself scored, ridged, or short | Turn and polish a new pivot (re-pivoting) | Pivot would be reduced below safe diameter | An undersized pivot flexes and wears rapidly |
| Missing or unrepairable component | Fabricate replacement to measured dimensions | Original can be economically reworked instead | Unnecessary remaking loses original material |
Tracing amplitude loss in a serviced watch to its real cause
Low amplitude after a watch service has several distinct causes: lubrication, endshake, mainspring condition, poise, or escapement health. Work through them in a fixed observational order before adjusting anything.
A systematic diagnostic order prevents you from 'fixing' symptoms with harmful adjustments. First inspect lubrication: wrong oil or oil spread onto the wrong surfaces increases friction at the balance and pallet pivots. Next check endshake and side-shake at each jewel, then examine the mainspring for set (loss of curvature), sticking, or insufficient power for the movement's design. Only after these come balance poise, staff condition, and the impulse and safety roller relationships.
Worked scenario — weak amplitude dial-up: A watch runs but amplitude is visibly low in the dial-up position. A plausible mistake is to conclude the mainspring is tired and fit a stronger replacement; the stronger spring raises torque through the train, increases sliding friction at the escapement, and can push the impulse pin toward overbanking, so the watch gains fault modes without gaining amplitude. The better decision is to inspect the balance cap jewel and its oil, verify correct oil on the pallet stones, and only then assess the mainspring against the movement's specification. Why it matters: amplitude problems usually have a friction cause that a stronger spring masks rather than cures.
- Check order: oil and contamination, endshake/side-shake, mainspring set and strength, poise and staff, roller and impulse relationships.
- Record amplitude reasoning in positions, not just one reading, so a position-dependent fault reveals itself.
- Treat any strengthening of mainspring power as a last resort, not a first move.
Fabricating replacement parts: from measurement to first-time fit
Fabrication practice should train the full chain — measuring the surviving mating part, turning and filing to size, and fitting with small corrections — rather than isolated lathe exercises.
For a missing or ruined part such as a cannon pinion, click, or small screw, the measurement stage decides everything. Measure the mating arbor's diameter and the depth of the seating with a micrometer and a depth gauge, note any deliberate friction fit (cannon pinions rely on controlled split tension), and sketch the part with its critical dimensions before cutting metal. Work to nominal sizes and leave finishing allowance only where a fitting operation will remove it.
Worked scenario — a cracked cannon pinion: A candidate turns a replacement pipe but reams the hole slightly undersized, forcing it onto the centre arbor. The friction is enormous, the hands drag, and the tight fit can eventually distort the arbor or split the new part. The better decision is to ream in small increments, test-fitting on scrap or the actual arbor until the pipe grips with a smooth, even tension that still allows the minute hand to set correctly. Why it matters: friction-fit parts are specified by feel as well as by dimension, and learning to hit that feel deliberately is the core of fitting work rather than lucky filing.
- Measure the surviving mate, not just the broken part; wear has changed both.
- Sketch critical dimensions — diameters, lengths, hole sizes, friction surfaces — before cutting.
- Finish friction fits by incremental reaming and test fitting, never by force.
- Slot and dress screwheads last, after the thread and head diameter are correct.
Clock mechanisms beyond the going train: striking work you must understand
Advanced clock service covers the striking and chiming mechanisms as systems: count wheel and rack striking differ in how they count and release, and servicing them means tracing each part's function on the bench.
Count wheel striking uses a notched wheel to determine the hour count, while rack striking uses a rack and snail that are gathered by a gathering pallet after release; the two designs fail in different ways. Learn to trace the sequence on any movement: warning, release, gathering, and the hammer action, plus the locking that stops the count. A practical drill is to hand-turn a striking movement slowly through one complete strike and name each event and each part that causes it.
Common functional faults follow from misadjusted geometry rather than wear: a hammer tail set so it catches wrongly, a gathering pallet that skips rack teeth, or a warning that is too short, letting the strike run past the correct count. When you service a practice movement with striking work, note the before-and-after relationships — locking depth, gathering pallet engagement, hammer lift — rather than just cleaning parts. That tracing habit is what distinguishes servicing a striking clock from merely cleaning one, and it is the kind of understanding an advanced clock assessment can probe from any angle.
Documenting a service the way a professional bench record works
Advanced service work is judged alongside evidence of method: measurements taken before intervention, parts replaced or remade, adjustments made, and results observed. Practise writing bench notes as you work, not afterwards.
A usable bench record for one movement should capture: the initial condition and symptoms; key measurements (pivot diameters, endshake, mainspring dimensions, timing observations in positions); the operations performed and why; any parts replaced or fabricated with their dimensions; and the final state, including lubricants used and post-service observations. The discipline of writing it during the job, with sketches and figures, forces you to measure before acting and gives you a reference when a fault recurs or an adjustment needs revisiting.
Turn this into a standing exercise: for every practice movement, produce a one-page record and then review it a week later against the movement's current behaviour. Ask three questions — could another person repeat this service from the notes alone; does every operation have a stated reason; do the recorded results match what you now observe? Weaknesses in the record usually expose weaknesses in the method itself: gaps where you acted on habit rather than measurement, or adjustments you made without a verifiable before-and-after.
- Before: symptoms, measurements, chosen intervention and justification.
- During: operations performed, dimensions of new or remade parts, adjustments and their before/after values.
- After: lubricants, timing or striking observations, and any follow-up recommendations.
A preparation sequence and honest readiness checks for DipPH-level bench work
Sequence your preparation across the three skill areas, cycling diagnosis, intervention, and fabrication, and use concrete bench milestones — not invented score predictions — to judge when you are ready to sit the assessment.
A realistic adaptable sequence: begin with two or three full services of a clock movement and a watch movement, each with complete bench notes, to re-establish baseline method. Move to corrective work — one bushing job, one mainspring replacement with justification, one escapement adjustment — chosen by diagnosis, not by convenience. Then run a fabrication block: one turned-and-fitted friction part and one threaded part, each from measurement to fit. Close with an integrated practice piece: one movement requiring diagnosis across going and striking work or timing work, serviced end to end under bench notes alone.
Readiness checks you can perform honestly: you can strip, service, and reassemble a clock and a watch movement and have them run correctly without referring to notes for method; you can justify every intervention you chose in your last three jobs; you can bush a plate and restore correct drop, lock, and side-shake on the first attempt; you can interpret timing observations in multiple positions and trace an amplitude fault through the diagnostic order; you can produce a bench record another horologist could follow. Treat each of these as a personal milestone to demonstrate on the bench — they measure your craft readiness, not any exam outcome, and official format and administrative details come from the BHI itself.
- Block 1 — baseline: full clock and watch services with complete bench records.
- Block 2 — correction: bushing, mainspring replacement, escapement adjustment, all diagnosis-led.
- Block 3 — fabrication: friction-fit part plus threaded part, measurement to fit.
- Block 4 — integration: one multi-fault movement serviced end to end from notes alone.
References and further reading
Use these references to explore the concepts and check the latest information from the relevant organizations.