← Back to Field Notes

June 27, 2025 · The Bloomfield Team

Manufacturing Inventory Management: A Practical Guide for Job Shops

A 40-person precision machine shop in Ohio conducted their first physical inventory count in three years last December. The ERP showed $1.4 million in raw material. The actual count came in at $920,000. The $480,000 discrepancy represented material that had been consumed without proper transactions, remnants that were scrapped without being written off, and bar stock that had been sitting in the rack so long the alloy certs were no longer valid for aerospace work.

Nearly half a million dollars in inventory variance for a shop doing $9 million annually. This is common. The typical job shop carries 18 to 25% of annual revenue in combined raw material and work-in-process inventory, and the accuracy of that inventory in the ERP system averages between 55% and 75%.

Why Job Shop Inventory Is Hard

Production shops making the same part in volume can set up Kanban systems, calculate reorder points with precision, and maintain tight inventory controls because demand is predictable. Job shops face a different problem. Every week brings a different mix of materials, quantities, and lead times. A shop might need 2" 304 stainless bar for one job, 6061-T6 aluminum plate for another, and Inconel 718 forgings with a 12-week lead time for a third.

Purchasing managers in job shops develop a reasonable strategy over time: buy slightly more than the job requires (to account for first-article scrap and setup material), stock commonly used alloys at minimum levels to avoid lead time delays on repeat materials, and maintain relationships with distributors who can deliver standard sizes within 48 hours. The strategy works operationally. It fails from an accounting and visibility standpoint because the remnants, excess cuts, and safety stock accumulate without systematic tracking.

The Cash Flow Impact

Inventory is cash sitting on a shelf. For a shop with $2 million in raw material inventory and 25% accuracy problems, approximately $500,000 is either misallocated (the ERP thinks it exists but it does not), obsolete (material that will never be used), or untracked (material that exists but is not in the system). That $500,000 could be a machine tool, two new hires, or a year of loan payments on an expansion.

Carrying cost for manufacturing inventory, including storage space, insurance, material degradation, and capital opportunity cost, runs approximately 20 to 30% of inventory value annually. On $2 million in inventory, carrying costs consume $400,000 to $600,000 per year. Reducing inventory by 20% through better tracking and purchasing discipline frees $80,000 to $120,000 annually.

A System That Works for Job Shops

Forget the warehouse management systems designed for distribution centers. Job shop inventory management needs three things: accurate material receipt tracking, consumption recording tied to job numbers, and remnant management.

Material receipt: When material arrives, it gets a transaction in the ERP that records alloy, size, quantity, heat/lot number (for traceability-required industries), and location. This transaction takes 60 seconds if the purchasing system is set up correctly. It creates the baseline that everything else depends on.

Consumption recording: When material is issued to a job, the quantity issued gets recorded against the job number. In shops with barcode scanning, this is a 10-second operation. In shops without scanning, a daily material issue log maintained by the saw operator or material handler captures the same data.

Remnant management: This is where most systems fail. When a job calls for 36" of 2" round 304 stainless and the purchased bar was 12 feet, there is a 108" remnant. That remnant needs a tag, a location, and a record in the system. Shops that manage remnants well assign a simple numbering system, store remnants by alloy and size, and include remnant inventory in the quoting process so estimators can quote from existing stock before purchasing new material.

The Quoting Connection

Inventory management connects directly to quoting accuracy and speed. When your estimator can see that you already have 200 pounds of 6061-T6 plate on the shelf, the material line on the quote changes from a purchased cost with a 5-day lead time to a zero-lead-time issue from stock. That shortens the quoted delivery by a week and reduces the material cost by eliminating minimum order charges.

Shops that connect their inventory system to their quoting process report faster quote turnaround on 30 to 40% of RFQs because the estimator does not need to request a supplier quote for material that is already in the building. The data in your ERP becomes an active participant in the quoting process rather than a static record that nobody checks.

Start with a Count

If you have not done a physical inventory in the last 12 months, start there. Count everything. Compare to the ERP. Document the variance by category (material that exists but is not in the system, material in the system that does not exist, material with incorrect quantities). That variance report is your roadmap for which process improvements will produce the largest financial impact.

Then implement cycle counting. Rather than a full physical inventory once per year, count a portion of your inventory each week. High-value and high-movement items get counted monthly. Low-value commodity stock gets counted quarterly. Within six months, your inventory accuracy will exceed 90%, and the financial picture of your operation will look fundamentally different.