There’s a version of this conversation that happens after the quote comes back. An engineer submits a spring spec, the price is higher than expected, the lead time is longer than the schedule allows, and the first question is why.

The answer is almost always in the drawing.

Design for manufacturability — DFM — gets talked about a lot in manufacturing circles, but rarely in specific terms that engineers can act on. This post does exactly that: connects the actual spec decisions you make on a spring drawing to what they cost and how long they take to produce.

What Design for Manufacturability Actually Means for Springs

DFM isn’t about cutting corners or accepting lower performance. It’s about making design decisions that accomplish your functional goals without creating unnecessary manufacturing complexity. In spring manufacturing, that complexity shows up in two places: cost and lead time.

Some spec decisions that look conservative or safe on paper — tighter tolerances, ground ends, non-standard wire sizes — add real cost and real days to your order without meaningfully improving performance in the application. Understanding which decisions do that, and which ones genuinely matter, is the difference between a well-optimized spring and an over-specified one.

Tolerance: The Single Biggest Cost Lever

Nothing inflates a spring quote faster than unnecessarily tight tolerances.

Tolerances on a spring drawing control the acceptable variation in wire diameter, outer diameter, free length, load at a specified height, and other parameters. Tighter tolerances require more frequent inspection, slower production rates, and in some cases, additional tooling. All of that has a price.

The important question isn’t “how tight can I hold this?” It’s “how tight does this application actually need?” For non-critical applications — a return spring in a light-duty mechanism, a clip in a consumer product — standard commercial tolerances are almost always sufficient and cost considerably less to produce. For a spring that’s seating a valve in a high-pressure fluid system, tight tolerances on load and rate may be exactly justified.

The mistake engineers make is applying the tightest tolerance category across the board as a safety margin. It protects nothing and raises costs on every line item.

Before finalizing tolerances, ask your manufacturer which dimensions are actually driving their inspection process, and which ones have natural process variation that lands well inside any reasonable tolerance band regardless. You may find you’ve been paying for precision you were already getting.

End Conditions: A Commonly Overlooked Cost Driver

Compression springs can be made with four basic end configurations: open ends, closed ends, closed and ground ends, and closed and squared ends. Each one is progressively more involved to produce.

Open ends are the simplest and fastest. Closed ends add a step. Closed and ground ends — where the end coils are ground flat to improve load distribution and allow the spring to stand perpendicular — require a separate grinding operation that adds both time and cost, typically 10–20% on a per-piece basis depending on quantity and spring geometry.

Ground ends are genuinely necessary in some applications. If your spring needs to bear against a flat surface with precise load distribution, or if solid height is critical to the assembly, grinding is justified. But ground ends are also frequently specified by default, without any functional reason, simply because they appear on a previous drawing or seem like the more professional specification.

If your application doesn’t require a flat bearing surface or precise solid height control, open or closed-but-not-ground ends will function identically at meaningfully lower cost and shorter lead time.

Wire Diameter: Stick to Standard Sizes

Spring wire is drawn to standard diameters — a fixed set of sizes that mills produce at scale and that distributors stock in volume. When you specify a wire diameter that falls between standard sizes, one of two things happens: the manufacturer substitutes the nearest standard size (and your spring doesn’t match the drawing), or they source non-standard wire, which takes longer to get and costs more per pound.

This is an easy problem to avoid. Before finalizing a wire diameter, confirm with your manufacturer that it corresponds to a standard size in your chosen material. If your calculated wire diameter lands between standards, adjust slightly — modifying the number of active coils or outer diameter slightly to compensate — rather than specifying a non-standard size.

The performance difference between adjacent standard wire sizes is typically small and adjustable. The sourcing difference is not.

Active Coils and Spring Index: Where Manufacturability Gets Physical

Spring index is the ratio of mean coil diameter to wire diameter. A low spring index means tightly wound coils relative to the wire size — a physically difficult geometry to produce consistently. Springs with very low index values (below roughly 4) require specialized tooling, slower production speeds, and more frequent quality escapes. They cost more and take longer.

If your spring design lands in low-index territory, it’s worth a conversation with your manufacturer before the drawing is finalized. There may be a geometry adjustment — a slightly larger coil diameter, a slightly smaller wire, or a change in active coil count — that gets you equivalent rate and load performance with a more producible design.

Similarly, very high active coil counts in a short free length create a high-density design that can be difficult to produce to consistent solid height. This is a less common issue but worth flagging if your design requires both a high coil count and a tight solid height tolerance.

Material Availability and Lead Time

Standard spring materials — music wire, 302 stainless, hard drawn — are typically stocked at spring manufacturers or available from wire distributors on short lead times. Specialty alloys — 17-7 PH stainless, chrome silicon, Inconel, Elgiloy — may require a material order before production can begin, adding days or weeks to the total lead time depending on current availability.

This doesn’t mean avoiding specialty materials when the application requires them. It means understanding the lead time implication and communicating your schedule early enough that material procurement doesn’t become the critical path on your project.

It also means being honest about whether a specialty material is actually required. If standard 302 stainless meets your corrosion and temperature requirements, specifying it rather than 316 or 17-7 PH by default keeps you in readily available material without a performance trade-off.

Secondary Operations: Spec Them Explicitly, Not By Implication

Shot peening, passivation, zinc plating, powder coating, end grinding — every secondary operation adds steps, adds time, and adds cost. None of them should be implied by the application or left for the manufacturer to assume.

If your spring requires a specific finish for corrosion resistance, specify the finish and the standard it needs to meet. If it requires shot peening for fatigue life in a high-cycle application, specify that directly. If it doesn’t require any secondary operations, say that too — it removes ambiguity and can actually speed up quoting and production.

The Value of Getting Your Manufacturer Involved Early

Every point in this guide is easier to address before the drawing is finalized than after. Once a spring is designed, tooled, and first-articled, changes cost real money and schedule. During the design phase, they’re a conversation.

If you’re working on a spring spec and you’re not sure whether a particular decision is justified or over-specified, that’s exactly the conversation to have with your manufacturer before you submit an RFQ. A manufacturer with real engineering depth — not just a quoting desk — will tell you where your spec is adding cost without adding performance, and where the tighter specification is genuinely worth it.

That’s the kind of input that improves both the part and the program it goes into.

If you have a spring design you’d like a manufacturability review on before you send it to quote, reach out to our engineering team. It’s a conversation worth having before the drawing is locked.