Finding the Edge

December 20, 2018 12:59 pm


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 S828HZ Wiggler and Center Finder Complete with Case and 4 Attachments




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 is located at the transition point between centered and offset, as shown in this video.

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

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



Mitutoyo 050101, Edge Finder, 3/8″ Dia. Shank, .200″ Dia. Tip




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 Full Warranty 54-575-600-0 Electronic Edge Finder with Cylindrical Tip, 0.200″ Stylus, 1/2″ Shank




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-Sensor




Another “creative” and accurate way to find the edge of the part is to use a Dial Test Indicator.

To do so you’ll need to have specific accessories defined as chair edge finders. These tools are usually equipped with magnets and are often machined in the shop.

PROS: It’s an extremely accurate way to find the edge of a part.

CONS: Chair edge finder needs to be machined


You can find our recommendations on dial test indicators here.




As always there’s no absolute best, and all the tools mentioned work equally fine and deliver great results.

If you have the money to invest, our recommendation is to go with the 3D sensor. It’s an extremely accurate tool, it saves time and it’s very easy and pleasant to use. If you don’t want to invest too much our choice is the mechanical edge finder.


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1 Comment

  • RICH

    I’ve never used a 3D style edge finder. They look impressive and I bet they really look spectacular when they get crushed by accident. That is, until you have to buy another.
    I’ve long used a standard edge and center finder. I still have the one that I smashed the point on by hitting “Z” down by mistake.. (Ouch!)
    Its replacement had a flat area on the edge finder part that would “click” as it made contact with the part, giving you an audible signal that you were very close to the part. Worked so nice, it got “stolen”.
    I have at times, used a ground rod in a collet or chuck and moved it close to the part. Then used feeler gages to find that distance between the part and the rod. Using good old fashioned math, I calculated the distance to move the spindle axis over the edge of the part.
    Of course there’s the time honored method of using an actual cutter and a slip of paper, too. Or, as I saw one fellow use a piece of masking tape which kept his fingers away from the spinning cutter. On a big Devlieg boring mill, you can’t always reach the tool and the controls at the same time, for example. But do be careful!
    Regardless, None of the various ways I’ve used or seen others use is dead accurate. But they got me close and with a little adjustment, I’m there.
    As you say, none are better than the others. Just depends on what you have to work with, what you need to get done, and what your skill set as a machinist is.
    As always, I’m impressed with the creativity of machinists. Over 45 years of doing this and I’m still amazed at what we do.


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