A turned part quoted at 100 pieces and the same part quoted at 100,000 pieces are not the same problem with a different multiplier. The cost structure changes shape, and so does almost every process decision around it.
Here is what actually moves when volume goes up on a CNC lathe.
At 100 pieces, three things dominate
Setup, programming, and first-article inspection. Each one is a fixed cost that lands on a small number of parts. A conservative program with an extra roughing pass costs nothing at 100 pieces because it saves a crash; at 100,000 the same caution is a permanent tax on every part.
That is why the volume quote is not "the prototype price divided by more parts". The process is re-planned before the price is set.
At 100,000 pieces, four numbers decide the price
Cycle time. Not the fastest operation — the slowest one. On a lathe with two turrets, the limit is usually the imbalance between them, not the cutting speed. Raising surface speed shortens cycle time until the tool life collapses, and then a tool change every few hundred parts eats the gain. Balancing the turrets is free; cutting faster is not.
Tool life measured in parts per edge. The relevant number is not insert price, it is insert price divided by parts per edge. A cheaper insert with half the life is a more expensive insert, and a mid-lot tool change costs more than either.
Scrap rate. At volume, scrap is a process property, not an operator property. Three causes account for most of it: bar-end remnants, tool breakage, and dimensional drift late in a run. All three are decided before the first part is cut — by bar size, by tool monitoring, and by whether the process has a control chart.
Material yield. Bar stock is bought to finished diameter plus allowance. Every extra 0.5 mm of bar diameter is metal that becomes chips on every single part. Reviewing bar size against the drawing before the first order is one of the cheapest savings available, and it is routinely skipped.
What changes on the shop floor
Programming
Prototype programs are written defensively: light first pass, generous clearance, slow feed on the uncertain feature. Volume programs are written for constant chip load, with the feed and speed tied to the material lot rather than to a catalogue page. The operator gets a setup sheet that says which insert, which offset, and what to do when the control chart moves — not just a program number.
Fixturing
At 100 pieces the fixture is whatever holds the part. At 100,000 the fixture is part of the process: dedicated collets, hard stops, pre-set tooling that stays with the job. The point is not speed of loading, it is repeatability between releases. The second batch should run on the same offsets as the first, so the parts do not drift between orders.
Unattended running
Bar feeders, parts catchers, chip conveyors and coolant pressure stop being accessories and become production equipment. The question is not "can it run lights-out" but "what stops it at 2 a.m." — a broken insert, a tangled chip, a bar that ran out. Each of those needs a detection method, otherwise lights-out is just unattended scrap generation.
Inspection
100% inspection at volume is a cost with no preventive value. Sampling at a fixed interval, plotted on a control chart with limits derived from process capability, catches drift earlier and costs a fraction of sorting every part. Gauge repeatability gets checked before the run, so a movement on the chart is the process and not the gauge.
Capability, stated as numbers
Volume claims are only useful if the capacity behind them is real and scheduled. At CHX Metal the turning capacity is 50 CNC lathes covering Ø1–300 mm, plus 70 Swiss-type automatic lathes for long slender parts where a guide bushing supports the workpiece at the cutting point. Total plant: 220 machines, 5,000 m², 5,000,000 pieces a month.
Turned diameters hold ±0.005 mm, verified on a CMM. Prototypes run 3–7 days, production 7–15 days from one piece. Repeating programs run against an annual contract with a fixed unit rate and weekly or monthly releases, so the price does not move with the order size and the delivery does not arrive as one large lot.
The question to ask a supplier
Not "what is your capacity" — everyone answers that with a big number. Ask instead:
- Which machines are assigned to my part number, and what else runs on them?
- What is the Cpk on the critical diameter, and how is it measured?
- What happens to the process when the bar lot changes?
- How does the program handle a broken insert at 2 a.m.?
- What ships with each lot — a certificate, or the actual inspection record?
A supplier who can answer those five has run volume work before.
More detail on the process side, including the cost breakdown and the SPC setup, is on the CNC lathe mass production page.
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