laser cut shims
Metal laser cutting for shim stock is the shaping of thin sheet into the washers, plates, spacers and profiled shims that set clearance, height or alignment in an assembly. The material is thin, the shape is usually simple, and the requirement that decides acceptance is rarely the outline: it is the burr, the flatness and the thickness, because a shim works by being exactly as thick as it claims and by sitting flat. This page covers what laser cutting does well on shim stock, where it stops, and how to specify a shim so the stack it belongs to actually closes.
1. What Shim Stock Is, and Why It Gets Laser Cut
A shim is a thin piece of metal inserted to take up a gap: under a bearing, between a flange and a housing, behind a motor mount, in a fixture where the height has to be tuned. It is often a simple outline — a disc, a rectangle, a horseshoe — sometimes with holes or a slot, and it is made in gauges from foil to about a millimetre.
Traditionally it is punched from strip, hand-cut, or bought as pre-cut stock and trimmed. All three have limits: a punch needs a die and leaves a rolled burr, hand cutting is only as accurate as the operator, and trimming stock to a profile wastes material and time.
Laser cutting removes the die and the hand work. A new outline is a new program, holes and slots come in the same pass, and a one-off can be cut the day the drawing arrives. That is why the route dominates prototyping, repair and low-volume shim work. It is also the part that is replaced first when a bearing wears, which is why small quantities are normal and a tooling charge is hard to justify.
2. Materials and Gauges
Four materials cover most shim stock.
Stainless steel — 301, 302 and 304 — is the default where corrosion resistance and spring temper matter. 301 in a spring temper is the classic shim material, because it holds load without taking a set.
Brass is chosen for bearing surfaces, electrical contact and machinability. It cuts cleanly and takes a fine edge, and it is often used where a steel shim would gall.
Aluminium serves weight and cost where corrosion duty is mild. It is soft, so a burr on aluminium deforms more easily under load than a burr on steel.
Carbon and spring steel appear where hardness matters and corrosion does not. They cut readily but need a finish, because a bare edge will rust in storage.
Gauge drives the process. Below a few hundredths of a millimetre the foil has no stiffness and handling becomes the limit; above about a millimetre the cut slows and the burr grows, and the economics start to favour a die. The gauge also decides which edge condition is achievable: thinner stock can be cut with a finer burr, while thicker stock needs a deburr step.
3. Laser, Die or Etching
The three routes trade differently.
A die is cheapest per part at volume and can combine blanking with forming, but it costs a tool, it leaves a rolled burr that has to be removed, and every revision is a tool change. For shim families with many sizes and modest quantities, the die rarely pays.
Chemical etching leaves no burr at all, holds very fine detail and does not distort thin foil, but it is slow and expensive as thickness rises, and it needs artwork and resist for every run.
Laser sits between them. It has no tooling, cuts any outline in one pass, and handles the middle of the gauge range well. Its cost is the cut length and the machine time, and its quality issue is the burr and the small heat-affected zone at the edge.
For a shim with a simple outline and a moderate quantity, laser is usually the right answer; for a fine-pitch washer in very thin foil, etching can be better; for a high-volume standard shim, a die wins. The choice is usually made on quantity and outline complexity rather than on the material.
4. Burr, Dross and Stack Height
A shim works by thickness, and a burr is thickness that was not asked for. On a thin shim the error is proportionally large: a burr of a few hundredths on a shim of a few hundredths is a double-digit percentage of the stack.
That is why burr has to be specified, not assumed. Laser cutting leaves a small dross bead on the exit side, and the amount depends on the gas, the focus and the material. On stainless the bead is usually small; on aluminium and brass it can be larger and softer.
The remedies are mechanical or chemical: a tumble deburr, an edge break by brush, or an electropolish that removes the bead and smooths the edge. Each adds a step and a cost, and each should be chosen against a stated burr limit rather than a general “deburr” note.
The exit side matters too. A shim that is stamped leaves a burr on one face; a laser shim leaves dross on the exit face. Which face is presented to the joint is a drawing decision. A supplier who cannot state a burr number is not inspecting the part that matters.
5. Flatness and Laminated Sets
Thin sheet is not naturally flat, and a shim that bows does not seat. The bow comes from the rolling stress in the strip, from the heat of the cut, and from handling.
Flatness should be specified on the face that seats, with a measurement method, and the packing should protect it. A stack of shims packed loose in a bag arrives with its edges bruised and its faces bowed. Where the stack is assembled dry, flatness dominates; where it is clamped hard, the burr dominates.
Laminated shims are the other case. A peelable laminated set is built from layers bonded together, and each layer is peeled away to tune the clearance. Cutting a laminated stack with a laser is possible, but the adhesive has to survive the cut without smearing the edge, and the layer count and bond have to be agreed with the supplier rather than assumed.
6. Tolerances
There are three tolerances on a shim, and they come from different places.
Thickness is a property of the material, not of the cut. It should be specified as a gauge with a tolerance class, and it is verified by measurement, not by the cutting process. A drawing that asks the laser to hold thickness has asked the wrong process.
The outline and the hole positions are the cut tolerances, and they behave like any laser-cut profile: good position, good repeatability, with a kerf compensation in the program. Position tolerance on the holes is what lets a shim drop onto a bolt circle without reaming.
Burr and flatness are the third group, and they are the ones that decide whether the shim performs. They are also the ones most often left off the drawing.
7. Prototype to Volume
Laser cutting fits the front of a shim program: a clearance trial, a repair shim, a one-off fixture, a family of sizes in small quantities. A new thickness or outline is a new program, and the turnaround is measured in days. A shim that costs cents at volume can cost dollars as a one-off, and the gap is almost entirely the tooling that laser avoids.
At volume the route changes. A standard shim in a fixed size is cheaper punched or etched in a panel, because the cut length per part stops dominating. The sensible programme keeps laser for the variants and tooling for the runner, and moves a variant to tooling only when its volume justifies it.
The handover is worth writing down, because a laser-cut shim and a punched shim are not dimensionally identical even when both meet the drawing: the burr direction and the edge condition differ. A shim family with ten sizes at fifty pieces each is a laser family, not a die family.
8. Inspection and Order Notes
Inspection covers thickness at several points, burr height on the exit face, flatness on the seating face, and the positions of the holes and the outline. For a laminated set, the layer count and the bond are checked as well.
An order should state the material and temper, the gauge and its tolerance, the outline and hole drawing with kerf compensation agreed, the burr limit and which face it applies to, the flatness limit and its datum, any deburr or finish, the quantity and the packing that protects a thin part.
The recurring mistakes are a thickness tolerance written into the cut callout, a burr limit omitted because “shims are thin”, a flatness figure with no datum, and a laminated set specified without agreeing the adhesive and the layer count. A thickness report that names the gauge and the measured points settles most disputes.
