Metal Parts Cost Reduction: Design Tips That Actually Work

I have spent most of the last two decades quoting metal parts, and the same lesson shows up in nearly every job. The drawing drives the price more than the machining time does. Two parts with identical dimensions can land at $1.80 or $9.40, and the difference is usually a few notes an engineer added without thinking twice.

This guide is about those notes. It walks through the design decisions that cut metal part cost without touching performance. I wrote it for design engineers and buyers who want the price down before the quote ever reaches their inbox.

The tolerance call is where most money gets lost

Tolerances are the single biggest cost lever in precision metal manufacturing. A hole called out at ±0.01 mm usually has to be reamed or honed, then measured on a CMM after the machine finishes. The same hole at ±0.05 mm falls out of a standard drill and is done. The part geometry did not change. The price did.

I watched a customer pay about 40 percent more for a simple bracket because one hole on the print carried a ±0.005 mm callout. That hole was a clearance hole for a cable tie. The designer had copied the tolerance from a locating feature on a different part and never went back to check it.

Before you tighten a tolerance, ask what the feature actually does. A dowel pin hole that locates a mating part needs the tight number. A through hole for a screw does not. A press fit bearing seat needs its numbers. A vent hole does not.

I think of it in terms of process capability. A shop running a tight Cpk on one dimension is not running tight everywhere. When every dimension is tight, the whole part gets slower, and the shop quotes for the slowest feature. Put the tight tolerance only on the features that earn it, and leave the rest at standard machining limits. This one habit removes grinding, honing, and inspection steps from the quote. Those are the steps that cost real money, and a relaxed callout simply removes them.

Pick the stock material before the exotic one

Material choice changes cost in ways that go beyond the raw bar price. A part in 316L stainless steel is fine. A part in a rare cobalt alloy can sit for three weeks waiting for stock to arrive, and the minimum order on that bar might be more than your entire lot.

Start with what is already on the shelf. 316L and aluminum 6061 are stocked everywhere and machine well. If you need more strength, 4140 and common tool steels are also easy to find. When a design calls for something unusual, ask whether a common alloy meets the same spec. A surprising number of exotic material requirements trace back to one property, and a heat treatment on a standard alloy often covers it.

Material also touches paperwork. If the part goes into a regulated assembly, the buyer usually needs a material certificate, and that is easy for 316L and 6061. For a special alloy, the cert trail gets longer and the lead time follows it. In automotive work the supplier often has to produce the full PPAP package with an IATF 16949 chain of custody, and that is simple on a stock grade and slow on a rare one.

I have seen parts specified in titanium where 316L would have done the job. Titanium machines slowly, wears tools out fast, and costs several times more per kilogram. It is a fine material when you need the strength to weight ratio, and a bad default when you do not.

The same logic applies to bar size. A part drawn from a 25 mm bar when the finished part is only 22 mm across wastes a lot of turned material. Match the raw stock to the finished part and you stop paying to machine away metal that should never have been there.

Simplify the geometry and kill the secondary operations

The geometry that quietly inflates cost is usually the feature that forces a second setup or a second process. Deep pockets, thin walls, sharp internal corners, and threads that run to the bottom of a blind hole all add time.

A sharp internal corner means a part cannot be cut in one pass. It forces either a smaller tool with more passes or a wire EDM step. A corner radius lets a standard end mill finish it in one go. Thin walls vibrate during machining, so the operator slows the feed to keep the part from singing, and the cycle time climbs with it.

Threads are a good example. A tapped hole is cheap when it is through and uses a standard size. A custom thread form, or a thread that must stop exactly at a shoulder, is not. Where you can, use standard inserts or off the shelf fasteners instead of a custom thread.

Undercuts deserve their own warning. An undercut is a feature the cutter cannot reach from the top, so it forces either a special tool, a fourth axis, or a second setup where the part gets clamped in a different direction. Sometimes an undercut is genuinely required, and the shop will quote for it. Most of the time, though, the undercut exists because the designer did not realize it would cost extra. A small draft angle or a redesigned wall removes it, and the part becomes a one setup job.

Every feature that needs a second setup, a second fixture, or a second machine adds labor and inspection. CNC machining rewards parts that come off in one or two setups. Design with that in mind and the quote drops.

Design for the process you actually plan to use

This is the mistake I see most often. A part drawn as a machined component goes to a shop that would happily make it by metal injection molding, and the whole geometry fights the process. Or a buyer asks for a casting but keeps wall sections so thin they will not fill.

Each process has its own rules. MIM handles small, complex parts in high volume and holds ±0.3 percent on many features, but it wants uniform wall sections and a sensible gate location. Investment casting manages complex shapes with draft angles and gives you a near net shape, so you skip most of the machining. Powder metallurgy is hard to beat on cost per piece when the volume is high and the shape is simple.

If you design a part before choosing the process, you get a compromise part that is expensive in every process. Pick the process early and let its constraints shape the design. The cheapest metal part is the one that does not fight its own manufacturing method.

Watch the batch size and standardize what you can

Setup cost is spread across the lot, which is why a 10 piece order and a 1,000 piece order look so different per unit. The first part is the expensive one. After that the machine is just repeating.

Small design changes can tip a part into a better cost bracket. If you combine two small parts into one, you remove an assembly step and a fixture. If you standardize a hole size across a family of parts, the shop buys one tool and keeps it in the machine. If you reuse a standard blank size, you stop paying for custom saw cuts.

Buyers sometimes order 20 parts a month and ask for a price that only makes sense at 2,000 a month. I understand the instinct, but it does not help. Tell the shop your real annual volume up front. A shop that knows the job runs all year can hold a fixture, stage raw material, and quote a number that reflects the repeat work, not a one off gamble.

Question every surface finish spec

Surface finish is a quiet cost driver because it looks like a small note on the print. A callout of Ra 0.4 µm across the whole part is a very different thing from Ra 0.4 µm on one sealing face.

I once quoted a housing where the entire exterior was specified at Ra 0.8 µm. That finish meant a second operation on every face and roughly doubled the machining cost. When I asked, the engineer said only the flange face sealed against an O ring. We relaxed the rest to a standard machined finish and the price came back down.

Specify the finish where it matters: the sealing face, the bearing journal, the mating surface. Leave the rest at the natural machined finish. If the part is cosmetic, say so, and let the shop suggest a cheaper route, like tumbling or a light bead blast instead of polishing.

If you are not sure what a realistic tolerance or finish is for your process, the FAQ on our site covers the common ranges. It is faster than a week of back and forth email.

Cost reduction in metal parts is not about squeezing the shop's margin. It is about drawing a part that does not ask for work it does not need. In the automotive and industrial work I handle most, the suppliers who win are the ones whose drawings are already easy to make. Loosen the tolerance that does not matter, pick a stock material, kill the second setups, choose the process before the geometry, watch the batch size, and question the finish. Do those six things and the price drops before you have negotiated a single line.