BOMs, shared parts, and valid quantities

A bottle is the parent item. Its body, cap assembly, and label are child items. A quantity on a BOM has a denominator: two seals per cap assembly is different from two seals per carton. Write that denominator beside every number. A correct multiplication using the wrong unit still gives an unusable plan. Northstar uses one body, one cap assembly, and one label per bottle. Each cap assembly contains one shell and two seals. To make twenty four bottles from scratch, the shop needs twenty four bodies, twenty four shells, forty eight seals, and twenty four labels. Exploding the cap assembly reveals its children; it does not create another demand for finished bottles. Check whether the listed parts are stocked assemblies or instructions to build an assembly. If ten complete caps are already usable, their shells and seals have already been consumed. Subtract those caps before exploding the remaining cap builds. Otherwise the same physical requirement appears twice, once inside the stocked cap and once as new loose parts. Versions matter because a drawing change may alter the recipe. Give each plan an effective date and a version identifier. In this exercise all bottles use version A throughout the horizon. A substitute seal is not automatically interchangeable: approval and fit must be established before its inventory can satisfy the requirement. Keep a small reconciliation next to the plan. The parent quantity should explain every child quantity through a visible path. A reviewer should be able to point to a line and say which parent created it. This is more valuable than a long list of parts with no relationship to the bottle starts. Do not attach yield loss to every level by habit. This lesson assumes perfect yield so the structural arithmetic can be checked first. Later lessons add losses at named operations. Separating structure from process assumptions makes a change easier to diagnose and avoids multiplying the same allowance twice. Northstar sells a small bottle and a large bottle. Both use one common cap, but each has its own body and label. Shared demand is added only after each parent has been exploded with its own recipe. The sum tells purchasing how many common parts are needed; the separate rows tell the planner who will be affected by a shortage. A shared part does not imply that finished products are interchangeable. A large bottle cannot cover a small bottle order simply because their caps match. Keep product-specific stock separate. Use a common component pool only for truly identical and approved parts. The planning table should retain both the common total and the contributing parent quantities. Packaging provides a useful unit trap. In this lesson a carton contains six bottles and partial cartons are allowed only for planning consumption: each bottle consumes one sixth of a carton equivalent. Purchasing orders whole cartons. Multiply the total bottles by the fraction, then round at the purchasing boundary. Rounding each product first can increase the order without a physical need. An engineering change has a date as well as a new part. Northstar changes the large bottle to a new cap in week three; small bottles keep the old cap. The old and new caps cannot substitute. The production start week determines the cap version in this exercise. Do not use the customer shipment date to choose the recipe unless that is the written rule. Now pause and test the plan with your own hands. Draw a row for each week. Name the unit at the top of each row. Put the input in one place and the result in a new place. Keep a copy of the first plan. Change just one fact, then run the sums once more. Ask what moved, why it moved, and who must act. If a date is too late, say so. If a part is not there, show the gap. If a count is based on an average, do not call it a sure thing. A plan is useful when the next person can check it and act on it. Write a short note that states the need, the choice, the risk, and the next check. Read it out loud to a peer. Ask that peer to find one weak claim. Use the feedback to make the plan clear. Each number should have a unit, a time, and a source in the case. Each change should have a reason. Each open gap should have an owner.

1. The planning question

   Original card with the two lesson goals.

   • Convert a product recipe into component needs without mixing units.
   • Combine multiple products while retaining a clear demand trail.
   • Northstar fictional case
2. Inputs and units

   Original table highlighting input quantities and dates.

   • BOM
   • Gross requirement
   • State timing
3. First calculation

   Original equation card showing the first worked case.

   • Base net purchases:19 bodies,10 shells,20 seals,18 labels.
   • For18 starts:13 bodies,4 shells,8 seals,12 labels. For30:25,16,32,24. For42:37,28,56,36.
   • With4 caps,20 cap builds need16 shells and32 seals net. With3 seals and10 caps,14 cap builds need34 seals net.
4. Second calculation

   Original table showing the second worked case.

   • Base old purchases26,new20; closing inventory0 in both pools.
   • Change in week4:old gross[18,30,30,6], total84, net44; new gross12,net2.
   • Change in week2:old gross[18,18,12,6],net14; new gross[0,12,18,12],net32. Total cap purchases46 in all three cases.
5. Stress the plan

   Original side-by-side baseline and revised result cards.

   • Change one input
   • Recompute dependent rows
   • Expose the gap
6. Commit with evidence

   Original checklist with an owner and next review date.

   • Retain assumptions
   • Check the result
   • Name the next action