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Edge Finder. Image Credit Nick Carter                  Optical Edge Finder. Image Credit: Tormach          Wiggler. Image Credit: Electrocomponents plc

Edge finders are tools used to locate the edge of a workpiece during machine setup operations by using an X and Y axis.  They are also referred to as center finders or wigglers, and are used in some machine spindles.

What is an Edge Finder?

Edge finders are used in machining applications to locate a specific distance on the edge of a machine part. They should be used before any work is done on the milling machine. It is composed of two concentric cylinders, spring loaded together. The machine spindle or other rotating tool must rotate in order to activate the edge finder. The concentric cylinders need to be offset so that the two halves slightly wobble as it spins. Then, move the part into the tool slowly. The edge finder will center up, and then break out of concentricity suddenly. At that point, reset the dial indicator or digital readout for that axis of the machine to a value equal the radius of the edge finder. Repeat the process at least once. 

How To Use and Edge Finder

Design Tip: Operate the edge finder at about 1,000 rpms during the process. View the edge finder from a 90-degree angle to get a better view of the kick.

 

Using an Edge Finder

Types of Edge Finders

There are several types of edge finders available. They can be simple, mechanical tools, electrically activated devices or optical.

  • Center finders are designed to locate markings on work pieces. They do not possess a spring-loaded tip, and operate when the spindle is stopped, as opposed to in operation.

Edge Finder. Image Credit: LittleMachineShop.com

  • Electronic edge finders are digital tools that locate work piece edges in addition to height offsets. They are battery operated and when an electrical circuit is formed by the edge finder an LED lights up.

Electronic Edge Finder with LEDs. Image Credit: Rotagrip

  • Wigglers are used to indicate the axis of the spindle. It is a pointer that can be accurately and easily located on the centerline of the longitudinal axis of the spindle to which is attached. Once the spindle is turning at 1000 rpms, the probe is centered and the user can visually center the workpiece under the spindle. The product comes in a kit with several probes that have a ball on one end to fit into the collet on the body.

Wiggler Edge Finder. Image Credit: MetalWebNews

  • Optical edge finder uses lighting to illuminate the workpiece or object being measured. The optical sensor has a set of lenses through which the reflected light passes. The light is focused on a camera that contains an optical chip with a light-sensitive pixel array. The chip converts the light-intensity value info an electronic signal with a corresponding value for each pixel called a "gray-scale value". An edge is found by determining where the gray-scale value between two neighboring pixels drastically changes. By combining this information with an XYZ coordinate location, the device is able to identify or create edges.

Basics of Optical Measurement. Image Credit: Quality Digest Magazine

Application

Edge finders are used in milling applications to find the edge of a part within a few thousands of an inch and can be placed inside the spindle head of a milling machine. 

Resources

Milling Machine

How an Edge Finder Works

The Wiggler

Understanding Optical Measurement