Find the Real Constraint
In many shops the constraint is not the polishing machines but the coating chamber or the one interferometer and the person qualified to use it. A part may wait days for a measurement slot between polish cycles, and each wait multiplies when a part needs several cycles. Measure queue time before each resource for a few weeks.
If most delay is waiting for the chamber or for test, adding polishing capacity will not shorten lead time. Schedule the constraint first and let other operations feed it.
Plan Coating as Batches
Coating cannot run one job at a time without wasting the chamber. Group jobs by compatible coating process, substrate and fixture size, and set a cut-off for each run. The tradeoff is clear: waiting to fill a run improves cost but delays shipping, while running half-full costs margin.
Many shops set a weekly or twice-weekly coating calendar and tell the planner which jobs must be polished and inspected by the cut-off. Late arrivals miss the run and wait for the next.
- Fixed coating calendar with cut-off times
- Compatible-process grouping rules
- Expedite rules and who approves a partial run
Account for Rework and Variable Cycles
Polish time is not a constant. A tight figure may need three test-and-correct cycles, while another part finishes in one. Use historical distributions by material and spec class instead of a single standard time, and plan with a buffer on the constrained operations.
When a job loops back, the schedule should show it as consumed capacity, not a surprise. If your ERP only supports linear routings, track rework as additional operations or in a simple board that planners trust.
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Machine Shop Scheduling Excel Template
An editable job shop schedule with machines, jobs, setup and run hours, due dates and priority. Includes scheduling model examples such as earliest due date and shortest processing time.
Blanks, Outside Processing and Tooling
Lead time on substrate blanks, especially crystals and infrared materials, can exceed the shop's own processing time. Treat blank due date as a start constraint, and flag long-lead materials at quote time. Outside processes such as specialty coating, edging or dicing need transit and queue time in the plan.
Tooling such as lap tools, test plates and fixtures should be checked for availability before releasing a job, because a missing test plate can stall a whole route.
Where AI Fits and Where a Whiteboard Is Fine
AI can help by learning realistic cycle and queue times from history, predicting which jobs will miss a coating cut-off, and answering what-if questions over live ERP data. Final sequencing and customer commitments should stay with the planner. If you run fewer than a few dozen open jobs and one chamber, a well-kept board and a weekly planning meeting may be all you need.
Frequently asked questions
What is the bottleneck in an optics shop?
Often it is the coating chamber or the metrology station rather than polishing. Because parts return for rework after measurement, a single interferometer can hold up many jobs. Measure queue time before each resource to see where jobs actually wait, then schedule the constraint first.
How do you schedule a coating chamber?
Treat it as a batch resource. Group jobs by compatible process, substrate and fixture, set a regular run calendar with cut-off times and decide how to handle partial loads and rush jobs. Align upstream polishing and inspection to the cut-off so finished parts are ready when the run starts.
Can ERP finite scheduling work for optics?
It can help, but only if it handles shared batch resources and rework loops. Many ERPs assume linear routings and fixed run times. If yours does not, use it for orders and materials and supplement with a constraint-based board or a purpose-built planning layer.
Netray can read your routings, cycle history and open orders so planners can ask which jobs will miss the next coating run, privately and on-prem.