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Finding the Edge

By Practical Machinist Sponsored Content

If you use a milling machine to machine parts, then you’re likely to be familiar with edge finders and the way they work.

Edge finders, sometimes also defined as wigglers or wobblers, are simple tools used to locate the edges of a workpiece or the center of a hole. They are also by far the most commonly used device to locate Part Zero.

They are held in a collet, end mill holder or chuck mounted in the spindle of a milling machine or drill press and come in different sizes and shapes, depending upon the inside diameter of the collet used.

There’s a whole choice of edge finders that work and function in different ways. Let’s take a look at them to better understand the advantages and disadvantages and hopefully help you to choose the best one for you:


The wiggler is a very common and popular type of edge finder. It comes with a number of different points, or probes, that go in inside the body. When the spindle of the machine is set the rotate, the center finder will begin to wiggle energetically. As it starts to move closer to the edge of a part, however, the wiggling will start to subside until the tool appears almost still.

PROS: Not affected by collet run-out

CONS: Requires the machinist to understand when the two sections are aligned, which can lead to inaccuracies.


Starrett Wiggler (002).jpg
Starrett S828HZ Wiggler and Center Finder Complete with Case and 4 Attachments

Mechanical Edge Finders

Mechanical edge finders are relatively cheap and work similarly to the wigglers. They have two sections: the body and the orbiting tip. The edge finder has three modes: orbiting, centered and offset. The edge of the part if located at the transition point between centered and offset, as show in this video.

PROS: Inexpensive and is not affected by collet run-out.

CONS: Requires the machinist to understand when the two sections are aligned, which can lead to inaccuracies.


Mitutoyo edge finder (002).jpg
Mitutoyo 050101, Edge Finder, 3/8″ Dia. Shank, .200″ Dia. Tip

Electronic Edge Finders

Electronic edge finders are designed to light up when in contact with the edge. They pass the current from the spindle of the machine all the way through to the part and have an LED light that indicates when the finder touches the part.

PROS: Very easy to read.

CONS: Affected by the collet run out


Fowler Edge Finder (003).jpg
Fowler Full Warranty 54-575-600-0 Electronic Edge Finder with Cylindrical Tip, 0.200″ Stylus, 1/2″ Shank

3D Sensors

3D sensors, sometimes also called 3D tasters, are probably the most practical and easy to use tools to find edges, although they are not cheap. Unlike the other tools listed, they can measure in X, Y, and also Z. The tip of the sensor is connected to a dial gauge. When the dial gauge shows zero, the spindle axis is exactly on the workpiece edge.

Since it’s not uncommon to break the tip, it’s generally recommended to buy one or two extras. You can buy extra tips here.

PROS: Extremely accurate and easy to use

CONS: Expensive


Haimer 3D taster (002).jpg
Haimer 3D-Sensor

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This aricle was prepared by Practical Machinist, which is solely responsible for its content. 

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