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:

 

WIGGLERS

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.

 

OUR RECOMMENDATION

Starrett S828HZ Wiggler and Center Finder Complete with Case and 4 Attachments

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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 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.

 

OUR RECOMMENDATIONS

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

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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

 

OUR RECOMMENDATION

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

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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

 

OUR RECOMMENDATION

Haimer 3D-Sensor

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DIAL TEST INDICATORS + CHAIR EDGE FINDERS

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

OUR RECOMMENDATION

You can find our recommendations on dial test indicators here.

 

 

WHICH ONE IS THE BEST?

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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5 Comments

  • Tony

    Moore Special Tool makes a chair type edge finder, this catalog shows one on page 16. No idea on the price.

    http://mooretool.com/pdf/F-1607%20Rev.%20A%20-Accessories%20Catalog.pdf

  • 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.

    “Chet”

  • CNCman74

    The most accurate way to find an edge is with a test indicator. Chuck the indicator in the spindle (use the swivel attachment), rotate by hand 360 adjusting the tip until it’s almost running true (needs a little offset or wobble 90 degrees to the surface you’re picking up). Move it to the surface and load up the dial with about 1/4 revolution. Rotate back and forth slightly to find the spot where the needle changes direction. Adjust the dial to 0. Raise the indicator up just over the top edge. Rotate 180 then carefully place a gage block on the surface loading the indicator needle. Again rotate back and forth slightly to find the spot where the needle changes direction. Move the axis halfway back to the 0. Go back to the other side and verify that the needle changes direction at the same spot on both sides. You’re there.

  • I recently upgraded to a 3d dial test indicator and it’s been amazing. I made the switch due to all the safety mechanisms put in these new machines where you can’t run the spindle with the door open, this makes it uncomfortable for me using a traditional edge finder especially when the door has safety bars all over and it’s hard to see the workpiece edge. The best solution is to get the wireless probe included in the purchase of the machine, we have one machine with one and it is very convenient.

  • I have always used a simple .200 diameter mechanical edge finder or a ground pin. I was never a big fan of the “chair edge finders”. If I needed be to that close. I pick up the edge with a mechanical edge finder and then use an indicator on the edge of the actual part and a ground block against the edge of the part. Here is a link to a much more detailed explanation of this method.
    https://www.practicalmachinist.com/vb/general/how-use-indicator-find-edge-145680/

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