Hot Presetting Springs: Locking in Load
Short answer: Hot presetting (also called scragging or setting) compresses a finished spring to a controlled overload — typically 1.05 to 1.5 times its working deflection — and holds it briefly so the wire yields plastically at the highest-stressed coils. When the load is released, the spring comes back shorter and its load at working height becomes stable. The result is a spring that holds its rated load instead of losing 2–8% of it in the first few thousand cycles. BQUQ runs this as a defined, recorded step on compression, extension, and torsion springs, with load verification before shipment and quotes returned in 12 working hours.
What Is Hot Presetting, Exactly?
Hot presetting is a permanent-set operation. You take a spring that has already been coiled, heat treated, ground, and shot peened, and you push it past its normal working range on purpose. The outer fibers of the most highly stressed coils exceed yield, the material takes a permanent deformation, and residual stresses redistribute through the wire cross-section.
The word "hot" is slightly misleading in modern practice. Traditional scragging was done at elevated temperature to lower yield strength and make the operation easier. Today, most production presetting is done at ambient temperature with mechanical overload — the industry still calls it hot presetting, and some shops do apply moderate heat (typically 150–250 °C) to assist the process or combine it with a low-temperature stress relief.
What matters for your design is not the name. It is what the operation does to the load-height curve.
The three things presetting changes
1. Free length. The spring gets shorter. A compression spring may lose 1–3% of free length on the first preset, and progressively less on subsequent cycles.
2. Load at a given height. The load at your working deflection drops once and then stabilizes. This is the number you actually care about.
3. Residual stress state. Compressive residual stresses at the inside of the coil improve fatigue life, which is why presetting is often paired with shot peening rather than replacing it.
Why Does a New Spring Lose Load in Service?
Every as-coiled spring carries residual stresses from coiling and from heat treatment. When you install it and cycle it, those stresses relax. The spring settles. Load at working height falls.
The magnitude depends on material, index, stress level, and how aggressively the spring is worked. For a typical cold-wound compression spring running at 40–60% of tensile, an unstabilized spring might lose 2–5% of its load in the first few hundred cycles and continue drifting slowly. For springs running at high stress or elevated temperature, the drift can be worse.
That drift is a real engineering problem. If your valve, latch, contact, or seal depends on a specific force window, a spring that starts at the top of the window and drifts downward will eventually fall out of spec — even though it passed incoming inspection.
Presetting front-loads that drift. You force the settling to happen in the factory, under controlled conditions, before the spring ever reaches your assembly line.
Preset vs. stress relief vs. shot peening
These three operations are often confused. They are not interchangeable.
| Operation | What it does | When it runs | Primary benefit |
|---|---|---|---|
| Stress relief (low-temperature) | Relaxes coiling and forming stresses | After coiling, before grinding | Dimensional stability, reduced brittleness |
| Shot peening | Imparts compressive surface residual stress | After heat treatment and grinding | Fatigue life |
| Hot presetting / scragging | Yields the highest-stressed coils to a set length | After heat treatment, grinding, peening | Load stability, free length control |
| Load testing | Measures load at specified heights | Final step | Verification, not modification |
A well-run spring line does all four in the right order. Skipping presetting because "the spring tested fine" is a common and expensive shortcut.
How Is the Preset Operation Actually Controlled?
The process is simple in principle and fussy in execution. The variables that matter:
- Preset height or preset load. Usually expressed as a deflection beyond solid or beyond working height. A common starting point is 1.1× to 1.25× the maximum working deflection.
- Dwell time. How long the spring stays compressed. Ranges from a fraction of a second on high-volume automated equipment to several seconds for large or critical springs.
- Number of cycles. Some processes preset once; others cycle the spring several times to a fixed height and let it settle.
- Temperature. Ambient for most springs; elevated for high-stress or large-wire applications.
- Rate of application. Slow, controlled compression avoids shock loading and inconsistent results.
Typical preset parameters by spring type
The table below gives indicative starting points. Actual values are set per part based on material, index, and stress analysis — treat these as a reference for discussion, not a specification.
| Spring type | Typical preset deflection | Typical dwell | Notes |
|---|---|---|---|
| Compression, cold-wound, small wire | 1.10–1.25× max working deflection | 1–5 s | Often automated in-line |
| Compression, large wire / high index | 1.05–1.15× max working deflection | 5–30 s | May use elevated temperature |
| Extension spring | Preset to a length past max working extension | 2–10 s | Careful with hook stress concentration |
| Torsion spring | Rotated past max working angle | 1–5 s | Legs and bends are the risk area |
| Belleville / disc | Flattened past working height | Short | Usually a separate flattening process |
After presetting, the spring is measured. If free length or load has moved outside the target band, the operation is repeated or the spring is scrapped. Presetting is not a fix for a spring that was wound wrong.
What Does Presetting Do to Your Tolerance Stack?
This is where presetting earns its keep in a real design. Two effects matter.
First, it tightens the effective load distribution. As-coiled springs have a natural spread in load at working height — wire diameter variation, coil diameter variation, and heat treat variation all contribute. Presetting does not eliminate that spread, but it removes the systematic drift component, so the population stays where it started instead of migrating.
Second, it lets you specify a tighter load tolerance honestly. Without presetting, a ±10% load tolerance at working height may be optimistic over the life of the part. With presetting and load testing, BQUQ can hold and verify tighter windows on critical springs. For CNC-machined components we work to ±0.005 mm; spring load tolerances are a different discipline, and the honest answer is that they depend on index, material, and how tight the wire supply is.
A worked example
Consider a compression spring, 1.2 mm music wire, 12 mm outside diameter, 8 active coils, free length 40 mm, working height 28 mm.
| Stage | Free length | Load at 28 mm | Comment |
|---|---|---|---|
| As coiled and heat treated | 40.0 mm | 18.5 N | Nominal target 18.0 N |
| After 1st preset to 22 mm | 39.3 mm | 17.4 N | 6% load drop, most of the settling |
| After 2nd preset | 39.2 mm | 17.3 N | Essentially stable |
| After 10,000 cycles at 28 mm | 39.2 mm | 17.2 N | Drift now under 1% |
Without presetting, that same spring would likely have arrived at the customer at 18.5 N and drifted to roughly 17.0–17.3 N during the first weeks of service — passing incoming inspection, then quietly moving out of the window. Presetting moves the drift to the factory floor where it can be measured and absorbed.
Which Springs Should Be Preset?
Not every spring needs it. Presetting adds cost, and on a low-stress spring with a loose load window it is wasted effort. It earns its place when:
- The spring operates at high stress (roughly above 40–45% of tensile for compression springs).
- Load must stay within a tight window over life.
- The spring sees elevated temperature, which accelerates relaxation.
- The spring is safety-related or the failure mode is a stuck mechanism.
- The application cycles heavily — millions of cycles.
- The spring is large, expensive, and worth stabilizing before installation.
When to skip it
Skip presetting when the spring is lightly stressed, when the load window is wide, when the spring is a one-shot actuator that never returns, or when the spring is a low-cost consumable where the added operation is not justified. A competent spring supplier will tell you when presetting is not worth the money — that conversation is a good test of who you are dealing with.
How Does BQUQ Run Presetting in Production?
BQUQ manufactures springs in one ISO9001 factory in Dongguan alongside CNC machining, metal stamping, and heat sink production. The spring line handles compression, extension, and torsion springs in music wire, stainless steel, phosphor bronze, and other common alloys.
The presetting workflow we use:
1. Design review. Confirm working height, load window, stress level, and expected cycle life. If the stress level does not justify presetting, we say so.
2. First-article preset. Establish the preset height and dwell that bring the spring to a stable free length and load.
3. Verification. Load test at the specified heights and record the curve. See our notes on spring load testing for how this is measured.
4. Production preset. Run the operation in-line with recorded parameters.
5. Final inspection. Load at working height, free length, and where required, a short cycle test.
Because the same factory runs compression springs, extension springs, and torsion springs, the preset parameters are set per part family rather than per supplier. That matters when a design uses more than one spring type and the load windows have to line up.
Where presetting sits in the sequence
Presetting is not the first or last operation. Get the order wrong and you undo the benefit.
| Step | Operation | Purpose |
|---|---|---|
| 1 | Coiling / winding | Form the spring |
| 2 | Stress relief heat treatment | Remove forming stress |
| 3 | End grinding (compression) | Square and flat ends |
| 4 | Shot peening | Fatigue life |
| 5 | Hot presetting / scragging | Load and length stability |
| 6 | Setting / adjustment | Fine dimensional control |
| 7 | Load testing and inspection | Verification |
| 8 | Coating or plating (if required) | Corrosion protection |
Note that coating comes after presetting. If you preset a plated spring, you risk cracking the coating at the coils. If you plate first and preset after, you damage the finish. Sequence matters.
Common Mistakes Buyers Make
Specifying load without specifying the preset condition. A load figure means nothing without the height at which it is measured and whether the spring has been preset. Write both into the drawing.
Assuming presetting fixes a bad design. It does not. A spring running at 70% of tensile will still relax, just more slowly. Presetting buys stability, not immortality. If your spring is failing, the fix is usually a redesign — our article on spring failure analysis walks through the common modes.
Confusing presetting with stress relief. They are different operations with different purposes, and one does not substitute for the other. The distinction is covered in more detail in our piece on spring stress relief.
Forgetting that extension and torsion springs preset differently. Extension spring hooks and torsion spring legs are stress concentrators. Presetting them requires lower overload and more care than a plain compression spring.
Not asking for the data. Ask for the load curve before and after presetting. A supplier who cannot produce it is not controlling the process.
Frequently Asked Questions
Q: How much load does hot presetting remove from a spring?
A: Typically 2–8% of the load at working height on the first preset, depending on material, stress level, and index. Most of that loss happens in the first operation and the spring is essentially stable afterward, with drift under 1% over subsequent cycling. The exact figure is measured per part, not assumed.
Q: Is hot presetting the same as scragging?
A: Yes. Scragging, setting, presetting, and hot presetting all describe compressing a spring past its working range to induce a controlled permanent set. Some shops reserve "scragging" for the elevated-temperature version and "presetting" for ambient, but in practice the terms are used interchangeably across the industry.
Q: Does presetting reduce spring fatigue life?
A: No — done correctly it usually improves it, because the operation redistributes residual stresses and is normally paired with shot peening. The risk is over-presetting, which can yield too much of the wire and cause coil contact damage. That is why preset height and dwell are set per part and verified by load testing.
Q: Can you preset a spring that is already installed in an assembly?
A: In principle yes, by over-traveling the mechanism, but it is rarely a good idea. You cannot measure the result properly, you risk damaging adjacent components, and the preset condition is uncontrolled. Presetting belongs in the spring factory where load can be measured before and after.
Q: What information do you need to quote a preset spring?
A: Material, wire diameter, outside or inside diameter, free length, number of coils, end style, working height or deflection, load at that height, expected cycle life, and operating temperature. Send those to sc@bquq.com and BQUQ returns a quote in 12 working hours, with flexible MOQ for prototype and production volumes.
Related Resources
- About BQUQ and our Dongguan manufacturing footprint: /about/
- Compression, extension, and torsion spring product pages: /compression-springs/
- Industry trends affecting spring and metal component sourcing: /industry-dynamics/
- Full technical article library: /bquq-blog/
- Frequently asked questions on tolerances, MOQ, and lead times: /faq/
- Case studies from precision component programs: /case/
- Talk to an engineer about your spring design: /contact/
Authored by the BQUQ Engineering Team. BQUQ (Dongguan) runs CNC machining (±0.005 mm), metal stamping, custom springs, and heat sink production in one ISO9001 factory. Source-direct from Dongguan, China — quote in 12 hours: sc@bquq.com | WhatsApp +86 13713157787 | www.bquq.com
