What is a custom metal shim?
A shim is a thin metal part used to take up a gap, set a preload, correct alignment or protect a surface from wear. Custom shims are made to a drawing rather than bought from stock, because the thickness, the outside and inside profile, the hole pattern and the flatness all belong to one assembly. The usual production routes are blanking in a press tool, fine blanking where a sheared edge has to be square and clean, laser cutting for low volumes and complex outlines, and double-disc grinding where the thickness itself is the controlled dimension. Thickness typically runs from 0.05 mm to about 3 mm. Anything thinner than about 0.20 mm is usually supplied as a laminated or peelable shim set so the assembler can adjust on the line instead of stocking a dozen discrete thicknesses.
What the shim is actually doing determines how it is made
Two shims that look identical on a drawing can need completely different processes. A shim that only fills space can be blanked from coil with a generous burr allowance. A shim that sets bearing preload or end float is a controlled-thickness part, and the thickness tolerance decides whether it is ground or rolled. A shim that sits in a sliding assembly or against a sealing face is a surface part, and the burr height and edge condition matter more than the dimensional tolerance.
- Gap filling and alignment — profile and hole positions dominate; thickness can sit at ±0.05 mm.
- Preload and end float — thickness is the controlled dimension, so the part is ground on both faces.
- Wear and galling protection — material and surface condition dominate; stainless or a plated grade is usual.
- Adjustment on the assembly line — supplied as a peelable laminated set rather than as single shims.
Materials and thickness range
- DC01 and DC03 mild steel — the general-purpose choice for gap and alignment shims where cost matters.
- DC04 deep-drawing steel — used when the shim has a formed feature rather than being a flat profile.
- 301 and 304 stainless — for corrosion exposure, food equipment and assemblies that must not rust.
- 65Mn spring steel — where the shim has to hold a load or resist taking a set.
- Brass, copper and phosphor bronze — electrical and thermal applications, and where a non-magnetic part is needed.
- Aluminium 1050, 5052 and 6061 — weight-critical assemblies; softer, so handling burr matters more.
Thickness runs from 0.05 mm to 3 mm. Below roughly 0.20 mm the material is hard to handle and hard to keep flat, which is why thin adjustment shims are normally supplied as laminated sets. Above about 3 mm the part stops behaving like a shim and is usually better specified as a machined spacer. Balford runs presses from 25 t to 350 t and deep draws to a maximum diameter of 250 mm, so shim profiles are well inside the tooling envelope.
Manufacturing routes, and which one your part needs
- Blanking in a press tool. The default for volumes from roughly 10,000 pieces upward. One hit produces the profile, holes and any notch. Tooling amortises quickly, and the process holds the profile and hole positions well.
- Fine blanking. Used when the sheared edge has to be square and largely burr-free, and when flatness after blanking matters. The tool is more expensive, so this route earns its place when the edge condition is a functional requirement rather than a preference.
- Laser cutting. The economical route below about 2,000 pieces, and the only sensible route for a profile that is still changing. Edges come off the machine with a small heat-affected zone and a light dross burr that is removed before packing.
- Double-disc grinding. Applied when the thickness is the controlled dimension. Both faces are ground at once, which holds thickness and parallelism far better than blanking from coil. Balford has this carried out by a qualified subcontractor, and the subcontractor is named on request and bound by the same confidentiality terms as the main order.
Key point
Choose the route from the functional edge of the part, not from its shape. If the drawing controls thickness on both faces, the part is ground; if it controls a sheared edge, the part is fine blanked; if neither is called out, blanking or laser cutting will do and you should not be paying for more.
What to put on the drawing
- Thickness with its own tolerance — not the general tolerance block. A shim whose thickness is governed by the general block is a shim nobody can inspect.
- Burr condition — permitted burr height, or a note that a rolled or deburred edge is required. State which face is the datum if only one face matters.
- Flatness — especially for thin blanked shims, which can bow slightly as the coil stress releases.
- Material grade and temper — DC01, 304, 65Mn and the hardness condition where it matters.
- Surface treatment — zinc plating, phosphating, passivation for stainless, or an oiled finish for storage.
- Annual volume and pack quantity — both change the tooling decision, and pack quantity changes how the parts are counted and de-burred.
Where shims go wrong
The most common failure is not a dimension — it is the edge. A blanked shim carries a burr on one face and a roll-over on the other, and if the shim sits against a bearing face or inside a sliding pair, that burr becomes the wear point or the interference. The second most common is flatness: a thin shim cut from coil arrives slightly dished, and the assembly measures a gap that the shim was meant to remove. Both are avoidable at the drawing stage, and both are cheaper to fix before the tool is cut than after.
Balford has been producing single-drawing dies since 2000 and has built more than 4,000 of them. Shim-type blanking sits inside that experience, including a 65Mn spring steel shim programme already in production. Work is quoted from the drawing, usually within 24 hours, with PPAP Level 3 as the standard submission level where a programme needs it, and quality management to ISO 9001:2015 with IATF 16949-aligned controls. Material certificates and inspection records come with the shipment.
Frequently asked questions
What is the thinnest shim you can produce?
0.05 mm is the practical floor for a discrete blanked or laser-cut shim, and handling it without damage is the hard part rather than cutting it. Below about 0.20 mm most assemblies are better served by a laminated or peelable shim set, where the part is built up from bonded foils and the fitter peels layers until the gap closes. Send the thickness and the adjustment range you need to cover and the stack can be specified on the drawing.
Can you hold a tight thickness tolerance on a shim?
Yes, when thickness is the controlled dimension the part is ground on both faces with a double-disc process rather than blanked from coil, and the achievable band depends on the starting material, the thickness and the flatness your assembly needs. Grinding is carried out by a qualified subcontractor. Give the thickness tolerance and the parallelism or flatness requirement on the drawing and we will confirm what the process can hold before quoting, rather than quoting a number the process cannot repeat.
What is the difference between laser cutting and blanking for shims?
Cost and edge condition. Laser cutting needs no tooling, so it is the economical route up to roughly 2,000 pieces and the right choice for prototypes and profiles that are still changing; the edge carries a light heat-affected zone and a dross burr that is removed before packing. Blanking needs a press tool, so it becomes cheaper above roughly 10,000 pieces and gives a cleaner sheared edge with consistent hole positions. Fine blanking sits above that when the sheared edge has to be square and largely burr-free.
Which industries buy custom shims?
Anything with a bolted or clamped joint and a stack of tolerances to absorb: automotive and motorcycle assemblies, pump and valve internals, gearbox and motor end-float adjustment, agricultural equipment, electrical switchgear, and instrumentation. The common thread is that the gap has to be controlled in production rather than designed out, and that the shim is cheap compared with the cost of machining the mating parts to a tighter tolerance.