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Written by G.L. Huyett Marketing Department on 05/13/2021 with 0 comments

Introduction To Shims

What Are Shims Used For?

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

Shim Use

What Are Metal Shims?

Metal shims are precision‑made 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 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.

Arbor Shims

Arbor shims (slitter shims) are thin, washer like discs designed 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.

Arbor Shims

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.

Variable Shims

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.

Variable Shims

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.

Variable Shims Use

Slotted Shims

Slotted shims come in a variety of shapes and can serve multiple purposes. Their common feature is an open, often U‑shaped, 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.

Slotted Shims

How Are Slotted Shims Measured?

Slotted shims are measured by their thickness and width as well as the slot depth and width. Shim height 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

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.

Shim Rings

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

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.

Shim Stock

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.

Shim Selection Guide

There are many things to consider when choosing a shim. Take a look at our infographic below to help make the decision easier!

Shim Selection Guide

Shimming

When shimming, be sure to keep in mind the following best practices and risks to reduce the likelihood of equipment failure.

Best Practices

  • Use no more than four shims.
  • Never shim more than an overall elevation of .150" in one application.
  • Sandwich thinner shims in between thicker shims to protect them.
Shimming

Risks

When a shim is used a small space is created above and below it. These spaces are compressed upon torqueing of bolts or during the operation of a mechanical component. As shims are added, more compression takes place, increasing the risk of slippage or undesired vibration of a mechanical component.

In addition to unwanted movement, additional spaces also increase opportunities of dirt and corrosion to develop. This can accelerate shim wear and cause premature failure.

Standard Shim Sizes

Shim sizing is often proportional to the size of the anchor bolts. For motor frame applications, shim size can be estimated based on the horsepower of the machine. Some standard shim sizes can also be determined based on standard motor frame numbers. Use the following charts to serve as a guide.

Shim Size Chart

Motor Frame Numbers
Estimated Shim Sizes and Horsepower Ranges

Want To Learn More?

Visit our product FAQs page to learn more about the shims we offer. If you have questions about a certain product or application, contact our experienced and friendly Sales team today!


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