Center Scope vs Edge Finder vs Touch Probe

Center Scope vs edgefinder Center Scope vs Touch Probe Edge Finder vs Touch Probe

Center Scope vs Edge Finder vs Touch Probe

Most machinists are accustomed to using either an edge finder or touch probe and will use a Centering scope as the last resort.  I think that after reading this post you will be grabbing your C-Scope first.  

Centering Scope vs Edge Finder

Traditional Centering Scope vs the TTS Digital Centering Scope (C-Scope)

To analyze why machinists do not use centering scopes often we must first investigate the limitations of a typical Optical centering scope.  Then we must see if these limitations apply to a modern Digital Centering Scope like the TTS C-Scope.

Parallax Error:

Parallax error on a traditional centering scope occurs because the cursor is drawn on a piece of glass between the user's eyes and the object being measured.  Since the cursor is not on the same plane as the object, a movement of your eyes will cause an apparent shift in the cursor (error). Parallax error does not exist on a digital C-Scope because the image sensor is fixed and does not move with respect to the object or the lens.  The cursor is then drawn directly over the image on a screen (ie: the same plane). Moving your head has no effect on the accuracy.


This may seem trivial but is probably the main reason machinists do not like using a centering scope.  Sticking your head into a machine and moving the axis at the same time is dangerous and awkward. On the other hand, using the C-Scope with a 6 foot USB cord brings you to your controls in a very comfortable position looking at a nice large computer monitor.  Excellent if you have impaired vision.


To calibrate a centering scope you need to rotate it in the spindle 180 deg.  This can be very cumbersome with a traditional optical centering scope. Mechanically calibrating a centering scope can be tedious.  Again with the C-scope this is very easily done with the included software. Welcome to the digital age where you can calibrate with a few clicks on your keyboard!


Since there are no moving parts on a centering scope, the accuracy is equal to your machine accuracy minus any movement of the scope with respect to your spindle. Focusing is done by adjusting the Z height of your machine.  The Z height remains consistent and can be stored in your tool table if you have a CNC machine. Therefore, as with most things machining, it is very important to have a rigid setup. The C-Scope is milled from a solid piece of aluminum which ensures that the lens and sensor of the scope do not move with respect to the spindle.  The ¾ inch shaft is made of hardened steel and can be mounted directly in a collet or the 10mm shaft version should be permanently mounted in a quality tool holder. For tenths accuracy, a mark can be made on the collet aligning with the USB cable on the C-scope so that it can be installed the same way every time.

A Powerful Measuring Tool:

Some people may say that a DRO replaces a Centering Scope.  This may be true for the traditional applications of a centering scope if you have accurate drawings to work from.  However, a DRO in conjunction with the C-Scope can make for a very powerful measuring tool.  A digital C-Scope will turn your milling machine into a very powerful system for taking quick and accurate measurements of odd shaped parts.  The measurements will be as accurate as your machine and most importantly measurement error will not add up. I have a video on reverse engineering which explains this. Traditional optical measuring tools are very expensive because they rely on the linearity of the optics to measure parts.  In the case of the C-Scope all measurements are taken at the crosshair intersection point. This point is always in the exact same location on the lens. This means that inexpensive optics can be used since linearity is not important. All measurements are taken with the movement of your machine so there is no lens or parallax error.  The Cscope is leveraging the accuracy of your machine to take accurate measurements.

Edge Finding:

Using a traditional Centering Scope as an edge finder is not common practice, mostly because they are awkward to use.  Now that we know the digital counterpart is fun to use, the question remains, will we use the C-Scope as an edge finder?  My bet is that you will… eventually. In Fact, the very reason that I designed this C-Scope was because I had just broken another expensive tip on my touch probe.  The Cscope can pay for itself very quickly if you tend to break your touch probe tips. I have designed the C-Scope to have lots of working room so that the lens is nowhere near your part where you could damage it. Edge finding edges with chamfers may require a refocus if the chamfer is significant.  Viewing edges with the Cscope may surprise you at how rough your edge actually is. In Fact, you may be wondering where you traditional edge finder would have picked up? Did it pick up on a burr or debris? With the C-Scope you can make an informed decision if you want to pick up at the high points, median or low points.  It is very easy to make pick up rough edges which would show up as noise on a typical edge finder.  Since it is a visual tool it tends to make you more aware of your machine backlash so you can properly compensate for it. After you get used to the C-Scope you may just find that using your traditional edge finder is like working in the dark...

Semi-Automatic part Inspection:

If you have a CNC machine you can write a program to automatically go to certain problematic areas of your part after machining has been completed but before you remove the part from your machine.  With a large screen at your disposal, it makes for extremely fast visual inspection. For example, you can check if chamfers are working well or inspect surface finish etc. A human operator can typically identify a problem by looking at a picture for less than one second.  Therefore you could do a detailed inspection of 10 points on your part in just over 10 additional seconds (depending on your machines rapids).  

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  • Tom on

    Rhianna, I am glad you mentioned laser edge finders, I should add them to the article above since they have one major flaw. Laser edge finders have a very large “Dot” which is viewed by the naked eye. This makes for a very crude measuring device compared to the visibility that you get viewing through a microscope. Also with the digital software calibration, there is no way you could get anywhere near the 0.0001" accuracy of the CScope.

  • Rhianna Hawk on

    My boss is looking to get a new edge finding tool for our workplace last I heard, and I think he may have heard about the benefits of the more modernized digital scopes that you mentioned. It’s great that centering scopes can work through software now without the traditional optical scope, and though I haven’t be trained on using the current unit yet, I’m pretty excited to get a new one so that I can start off with the modern tech. I’ll be sure to pass on your tips about how to focus using the z-height of the machine, as you describe, to the shop team.

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