Precision Shims and Spacers: The Unsung Stamped Part
Short answer: stamped shims and spacers are made from strip 0.05–3.0 mm thick, and a good progressive die holds outside dimensions to ±0.02–0.05 mm, hole positions to ±0.03 mm, and flatness to a few hundredths of a millimetre on small parts. Thickness comes from the incoming strip, not the die, so thickness tolerance is a material spec — typically ±0.01–0.03 mm on precision strip. They are cheap, invisible, and the part nobody thinks about until a rotor binds, a bearing walks, or a stack-up tolerance fails.
Ask a machine builder what keeps a motor stack at the right height, a gear train silent, or a bearing preloaded, and the answer is often a handful of thin metal discs that cost less than the coffee on their desk. Shims and spacers are the adjustment mechanism of the mechanical world: they set gaps, control stack-up tolerance, and compensate for machining variation. Because they are simple, buyers assume they are easy to source well. In practice the tolerances that matter — thickness, flatness, burr — are exactly the ones that are easy to get wrong. Here is what a stamping shop checks before quoting yours.
What Shims and Spacers Actually Do
A shim is a thin part used to adjust clearance or alignment; a spacer is a part that maintains a fixed distance between components. The functions overlap, and the drawing usually names the part after its job. The common requirement across both is a precise thickness, a flat surface to bear against, and a clean edge that will not damage what it touches. In motors and gearboxes, shims set bearing preload and end play, often to 0.01–0.05 mm of adjustment. In assemblies, spacers stack around fasteners to hold PCB-to-housing or component-to-frame distances, where height tolerance accumulates across the stack.
The failure modes are instructive. A shim that is 0.03 mm thicker than nominal changes bearing preload enough to shorten life. A spacer with a burr on the bore face can tilt a PCB and break a solder joint. A shim with internal stress will not lie flat and will rock under load. None of these parts are exotic; all of them fail quietly, which is why precision matters more than the part price suggests.
Thickness: The Tolerance You Buy, Not Stamp
There is one fact about shims that surprises most buyers: stamping does not control thickness. The die cuts the outline and the holes, but the thickness of the part is the thickness of the incoming strip. So a thickness requirement of ±0.01 mm is a material specification, not a die specification, and it must be written on the drawing as such. Precision-rolled strip is available with thickness tolerances in the ±0.005–0.03 mm range depending on material and width, and the cost of the strip rises as the tolerance tightens.
This drives a design rule: specify the tightest thickness tolerance only over the functional area if possible, and never tighter than the strip can be rolled. When a shim must provide very fine adjustment, designers often use laminated (peelable) shims — stacks of thin layers bonded together that the assembler peels down to the needed thickness. Stamped peelable shim packs are a specialty product, and the stamping challenge is cutting the pack without fusing the layers at the edges. The general tolerance landscape for stamped parts, including what is realistic on thin materials, is in the metal stamping tolerances guide.
Flatness, Crossbow and Internal Stress
A stamped shim does not come out of the die perfectly flat. Shearing leaves a burr side and a roll-over side; coining, if used, sets stress; and thin material carries whatever curvature the coil had, called crossbow. Flatness problems show up as rocking parts on an assembly fixture or as gaps under a bearing face. The die designer controls flatness three ways: by keeping the blank geometry balanced, by adding a light coining or flattening station that pushes the part flat between flat die faces, and by controlling the direction the part is stripped from the die.
For very thin parts, 0.05–0.15 mm, flatness is genuinely hard because the part is flimsy and handling deforms it as easily as stamping does. Parts below about 0.1 mm are frequently handled on a carrier or in arrays, and measured on an optical comparator or with non-contact probes rather than calipers that bend them. When the application needs dead-flat, burr-free edges and tight thickness, fine blanking is the process to compare — it produces a full-shear edge and excellent flatness. The fine blanking guide explains when its higher tooling cost pays back.
Burr: The Edge Problem Nobody Puts on the Drawing
Every sheared edge carries a burr, and on shims and spacers the burr is a functional defect: it raises the effective thickness at the edge, cuts into mating surfaces, and contaminates clean assemblies. The drawing should state a maximum burr height — a common practical value is 0.02–0.05 mm on general parts, tighter where the part bears on seals or precision faces — and should state the acceptable direction where that matters. Direction is a die-design output: the burr always appears on the side of the punch exit, so flipping the part in the die flips the burr.
Where burr cannot be tolerated at all, the options are fine blanking, a shaving operation, or a light deburring pass such as drag finishing or micro-abrasive blasting. All add cost, so the smart move is to specify only the edges that matter. The bore of a spacer that slides over a shaft needs its burr removed or it will score the shaft; the outside diameter may be cosmetically irrelevant. Edge requirements should be drawn edge-by-edge, and our engineers will push back on a blanket "deburr all edges" note because it prices up parts that only needed one controlled edge.
Materials: Matching the Shim to the Job
| Material | Typical thickness range | Typical use |
|---|---|---|
| Low-carbon steel (DC01, SPCC) | 0.10–3.0 mm | General spacing, low stress |
| Spring steel (C67, CK75, 301 SST) | 0.05–1.5 mm | Preload shims, snap applications |
| Stainless 304 / 430 | 0.05–3.0 mm | Corrosion, food, outdoor |
| Brass (C260, C268) | 0.10–2.0 mm | Corrosion resistance, non-magnetic, bearing shims |
| Phosphor bronze (C5191) | 0.05–1.5 mm | Springiness plus corrosion |
| Aluminum (5052, 6061) | 0.20–3.0 mm | Lightweight spacing, heat transfer paths |
| Peelable laminate (steel) | 0.05–0.15 mm per layer | Fine adjustment in the field |
Material choice for a shim follows the environment and the load. Steel is cheapest and fine for dry indoor spacing. Corrosion and humidity push you to stainless or brass. A shim that must provide spring preload needs spring temper, and a spacer in a thermal path should be aluminum or copper rather than steel. Note that spring-temper strip is harder to stamp flat and holds tighter tolerances on form — a trade worth knowing before the drawing is frozen. Material selection across stamped parts is covered in more depth in the stamping materials guide.
Tolerance, Tooling and What to Send
| Feature | Typical stamped capability (indicative) | Fine blanked capability |
|---|---|---|
| Outside dimension | ±0.02–0.05 mm | ±0.01–0.02 mm |
| Hole position | ±0.03–0.05 mm | ±0.01–0.02 mm |
| Flatness (small thin part) | 0.02–0.05 mm | 0.01–0.03 mm |
| Burr height | 0.02–0.05 mm typical limit | Near zero on full-shear face |
| Edge quality | Shear + fracture zones | Full shear, no fracture |
| Tooling cost (indicative) | $2,000–$15,000 progressive | $8,000–$40,000+ |
The numbers above are indicative ranges for conventional progressive stamping on thin strip; the actual capability depends on material, thickness, part size, and tool construction. When you send a shim or spacer drawing for quotation, include the functional requirements explicitly: which faces bear, which edges must be burr-free, the flatness datum, and the true thickness tolerance zone. A drawing that just says "shim, 0.5 mm thick" will be quoted at the cheapest interpretation — and the parts may rock, bind, or cut their neighbors.
Frequently Asked Questions
Q: What thickness tolerance can I actually get on a stamped 0.2 mm steel shim?
A: The die holds the outline, but thickness comes from the incoming strip. On precision-rolled low-carbon strip, ±0.01–0.02 mm thickness is realistic; typical mill strip runs ±0.02–0.03 mm. State the thickness tolerance as a material requirement and verify incoming coils if it is functionally critical.
Q: How flat can a stamped shim be?
A: On a small, thin part with a flattening or coining station in the die, flatness of 0.02–0.05 mm is achievable in production. Very thin parts below about 0.1 mm are limited by handling as much as by the die, and dead-flat, burr-free requirements usually point to fine blanking or a flattening operation after stamping.
Q: How do I remove the burr from a stamped spacer?
A: Specify the maximum burr height and the acceptable direction on the drawing first — often only one or two edges truly matter. For zero-burr edges, options are fine blanking, a shaving station, or a secondary drag-finish or blasting pass, each at a different cost. Blanket deburring of every edge is usually wasted money.
Q: What is the minimum order quantity for custom stamped shims?
A: That depends on tooling cost versus piece price. A simple round shim die is inexpensive and small runs of tens of thousands make sense; complex progressive or fine-blank tools need larger volumes to amortize. Ask for the tooling amortization curve — our quote shows tooling and piece price separately so you can see the crossover.
Q: Should I use laminated peelable shims or individual thicknesses?
A: If the exact needed thickness varies by unit in assembly, peelable laminated shims let the fitter peel to a precise stack height on site. If the thickness is fixed by design, individual stamped shims at each thickness are cheaper. The peelable option costs more per set and needs careful edge handling to avoid layer fusion at the cut.
Related Resources
- Fine blanking guide — when full-shear edges justify the tooling.
- Metal stamping tolerances guide — realistic ± numbers across stamped features.
- Stamping materials guide — matching strip material to function.
- About BQUQ — ISO9001 factory in Dongguan stamping precision thin parts every day.
- Contact us — send your shim drawing for a 12-hour quote at sc@bquq.com.
Authored by the BQUQ Engineering Team. BQUQ is an ISO9001-certified source factory in Dongguan, China, running CNC machining, metal stamping, custom springs, heat sink and collet lines under one roof. Send drawings to sc@bquq.com or WhatsApp +86 13713157787 for a quote within 12 working hours. www.bquq.com
