INTRODUCTION OF SHIMS

Metal shimsare precisionmade shims from a variety of metals including carbon steel, alloy steel, spring steel, stainless steel, and brass. Metals shims are more durable and offer tighter tolerances than other types of shims.

What Are Shims Used For?

Shims are used for taking up excessive tolerances and gaps in assemblies like automotive body panels, electric motor mounts, and many other applications. In machining applications, shims are engineered to specific tolerances for use in precise machinery positioning.

What are the Different Types of Shims?

Different types of shims include arbor shims, variable shims, slotted shims, shim rings, and shim stock. While they are all used to take up excess tolerances, they each provide unique value to specific applications.

Each type of shim has different designs and features to make them suitable for different applications.  

Arbor Shims

Common Names: Shim, Slitter Shim, Shim Washer.

Applicable Standards: None known.

Fabrication: Most commonly made from high carbon steel, also known as blue tempered, stainless steel, or brass. Other materials not standard, but are used.

Common Uses: Used for fast, accurate spacing of milling cutters, gang cutters, saws, slitting blades, and grinding tools.

Comments: Some versions made from 1010 full hard material, which is more pliable but has less wear properties than blue tempered. 

Arbor shims (slitter shims) are thin, washer likediscsdesigned to prevent axial movement in assembled components. Arbor shims are machined to specific tolerances for an exact fit and used in machinery alignment applications on milling cutters, saws, and grinding tools.

How Are Arbor Shims Measured?

Arbor shims are measured by their thickness, outer diameter, and inner diameter. When ordering, arbor shims are identified by their inner diameter and thickness.

It is important to know that there are arbor shims and spacers, and they are different fasteners. Arbor spacers feature a keyway that allows it to slide over a keyed shaft, which is a characteristic required for use on milling machines, slitting saws, and other similar applications.

Variable Shims

Common Names: Variable Shim, Lengthening Shim, Shoulder Screw Shim, Stripper Bolt Shim.

Applicable Standards: None known, though ID and OD match the mating dimensions of a stripper bolt.

Fabrication: Stamped from spring steel, or medium to high carbon grades, 1045 – 1095.

Common Uses: Used to increase the effective length of shoulder bolts/stripper screws by installing over the threads but remaining beneath the stepped shaft of the stripper bolt.

Comments: Stripper bolts are used in tool and die work to hold stripper plates in place. Stripper plates guide the punch tip in a stamping operation and this controlling parallelism is important.

Variable shims are divided into two categories: shortening and lengthening. They are used to lengthen or shorten the effective length of shoulder bolts (aka shoulder screws or stripper bolts). Shortening shims are placed over the shaft under the head of the screw to shorten it, whereas the lengthening shims are placed at the base of the shaft over the threads. Variable shims are often used in punch and die assemblies. 

How Are Variable Shims Measured?

Variable shims are measured by their thickness, as well as inner and outer diameter. The inner and outer diameter are necessary when ordering.

Slotted Shims

Common Names: Slotted Shim, Horseshoe Shim, Slotted Motor Shim.

Applicable Standards: Stainless steel and plastic are most common. Sizes are called out using letters representing the squared dimensions of the slot.

Fabrication: Designed with a bolt slot to ease installation. Stainless steel is most common.

Common Uses: Used to level motors and machinery, especially to ensure the alignment of components, such as a motor to a pump.

Comments: The tab allows for safe installation without risk to operator to crush fingers. Do not shim more than .150" and use thicker shims on either side of thin shims to minimize wear.

Slotted shims come in a variety of shapes and can serve multiple purposes. Their common feature is an open, often Ushaped, slot. They can be fitted around existing bolts and screws or used as regular spacers. Some slotted shim varieties are fitted with tabs for easier insertion. 

How Are Slotted Shims Measured?

Slotted shims are measured by their thickness and width as well as the slot depth and width. Shim length is also measured, however the added length of a tab (if present) is not factored. Additionally, slot width is measured from the narrowest section of the slot and does not apply to the tapered opening. When ordering, slotted shims are identified by their width, length, and thickness. 

Shim Rings

Common Names: Support Washers, Round Shims, Support Rings, SS Shim Ring, Backup Ring.

Applicable Standards: DIN 988 SS series.

Fabrication: Usually stamped from spring steel to HRC 44 – 49. Larger sizes sometimes machined from tubing with ground side faces.

Common Uses: Used between machine components. Often used to provide a flat and solid surface for a retaining ring that retains components against a shaft.

Comments: Generally much more expensive than DIN 988 PS series due to more precision in manufacturing. No imperial standards.

Shim rings, also called tolerance rings, are used in stamped, molded, or worn housing to form a tight hold on bearings. They are often used in concert with retaining rings and used to take up play between machined components. 

How Are Shim Rings Measured?

Shim rings are measured by their thickness, inner diameter, and outer diameter. When ordering, shim rings are identified by their inner diameter and thickness.

Shim Stock

Common Names: Shim Stock, Shim Rolls, Rolled Shim.

Applicable Standards: While there are no known standards, thickness tolerances are carefully controlled, as is the material content.

Fabrication: Rolled or flat sheets. Rolled is more economical to manufacture, ship, and store, though flat sheets tend to work better when trying to cut a large piece to size, as the rolls tend to want to reroll and not stay flat until installed.

Common Uses: Primary use is in tool and die alignment. Also used for automotive and truck axle shims.

Comments: Color coded plastic stock eliminates need to check thickness with a micrometer. Custom cut edges need to be deburred before installation.

Shim stock is thin precision stock material from which custom shims can be cut. It is a versatile material that can easily be cut to specific sizes using scissors or metal shears. Shim stock is typically used for support, leveling, and fit adjustment.

How to Measure Shim Stock:

Shim stock is measured by its thickness, length, and width. When ordering, shim stock is identified by all three measurements.

How to Use Shim Stock:

To use shim stock, follow these steps:

1. Measure the clearance needed for take up using a feeler gauge.
2. Select the closest size of shim stock.
3. Cut the shim stock to the length and width needed using shears or scissors.
4. Slip the cut shim stock into the desired space.