The Science Of Roundness
1,010,638
Published 2019-01-11
If we take the fulcrum point of a lever and move it completely over to one end, duplicate it repeatedly, witch each copy sharing the same fulcrum; a new simple machine is formed - the wheel.
Wheels allow us to multiple distances, speed, or force based on how much leverage we put on their center point.
Wheels provide another characteristic that has been critical to industrial growth. The ability to reduce friction by transmitting forces at a single point.
Roundness, along with size play critical roles in how parts are specified, designed and fitted. However, roundness diverts from the standard methods of defining dimensions such as length, area, and volume. Roundness is more of a relationship between dimensions and must be measured in a completely different manner. The measure of roundness, as well as other metrics of dimensionality, is known as metrology - the scientific study of measurement.
The ability to verify the roundness of a part is absolutely critical to a component’s performance.
In the intrinsic datum method, the datum points used for measurement are directly taken off the part and it contacts point with a reference surface. Typically a flat surface is used for a single datum measurement or a V block for a two datum measurement.
A measurement device that measures the displacement of the surface, such as a dial indicator, is brought to the surface of the part and zeroed to a start point. As the part is rotated, deviations from roundness displace the measurement tool from zero, with surface peaks creating positive displacement and valleys negative ones.
The solution to the limitations of the intrinsic datum method is extrinsic datum measurement. Extrinsic datum measurement is done by assigning a rotational axis datum to the part and aligning it the circular datum of a highly accurate rotating measuring fixture.
The four common types of calculated references circles are:
Least Square Reference Circle (LSC)
Minimum Zone Circle (MZC)
Minimum Circumscribed Circle (MCC)
Maximum Inscribed Circle (MIC)
The Least Square Reference Circle (LSC), the most commonly used reference circle, is a circle that equally divides the area between the inside and outside of the reference circle.
A Minimum Zone Reference Circle (MZC) is derived by first calculating the smallest circle that can fit inside of the measured data. Then calculating the smallest circle that can encompass the measured data. The out-of-roundness is given by the radial separation between these two circles that enclose the data.
A Minimum Circumscribed Reference Circle (MCC), sometimes known as the ring gauge reference circle and is the smallest circle that totally encloses the data. Out-of-roundness is quantified as the largest deviation from this circle.
A Maximum Inscribed Reference Circle (MIC) is the largest circle that can be enclosed by the data. The out-of-roundness
is quantified as the maximum deviation of the data from this circle. This is sometimes known as the Plug Gauge Reference Circle.
When rotating parts are examined, especially by extrinsic measurement, harmonics of the part become a consideration. Irregularities that exist on a rotating part that happens rhythmically are known as undulations.
In 2011, the International Committee for Weights and Measures spearheaded an effort to redefine the kilogram, moving it away from antiquated reference objects. One proposal, pushed by an international team called the Avogadro Project, aimed to define the kilogram in terms of a specific number of silicon atoms. In order to count the atoms of the large silicon-28 crystal, it was ground into a ball and its volume determined.
Moving past man-made objects, let's look at the roundest object ever measured. In 2013, in an effort to study the distribution of charge around the electron, scientist at Harvard were able the measure the smallest roundness ever.
All Comments (21)
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Fun fact: The red tip on the end of the probe (in the thumbnail photo) is actually a precious Ruby gem. I was a machinist for several years and worked in the CMM room occasionally where precision parts were measured in x, y, and z axis. They use a Ruby tip on the probe because it can touch objects many thousands of times without wearing out or becoming disfigured or flattened on the end, from repeated long term use. It maintains a perfect surface tip for touching and measuring with precise accuracy for repeated regular use over extended periods of time, as an accurate precise measuring device. Once the probe touches a part in many points, in all axises the computer gets a picture of exactly what the part looks like, in order to maintain continuity of accuracy in the production process of the parts being machined.)
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Wow, that "125 feet" comparison made me realize how incredibly well made ball bearings actually are. Amazing video, thank you.
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This and the History Guy are what needs to be on Discovery Channel instead of all that reality TV programming.
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"The wheel is a bunch levers organized in a circle." Whoever invented the wheel got discredited so hard
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Got here from the Flatness video, this one is well done as well for a high level introduction. A great follow-up to this one would be a GD&T specific video on the differences between circularity (roundness), cylindricity, run-out, and total run-out. You may find your word choice in this video isn't quite as precise as it needs to be if you dive into that rabbit hole. Well done nonetheless.
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as a former specialist in the field of measurement technology i approve this video
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I’m a retired mechanical engineer and I’m just loving your descriptions. Stuff that I’ve intuited you have expressed wonderfully.
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I’m planning on studying mechanical engineering this fall, and these videos are getting me even more pumped for it.
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Roundness is directly proportional to the volume of beer I consume in a given period of time. I am now perfectly round as I have optimized my consumption of beer.
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came here from the "science of flatness" video. This was just as good. Keep up the great videos my friend.
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when you try to drill a thin sheet of metal, most of the time the drill hole is a reuleaux triangle. i never realized that this shape has a constant diameter, it all makes sense now since the drill bits are almost a line in their cross section.
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I used to have to change tools in a horizontal mill and tram them in to less than 50 millionths TIR , the set the front of the insert to 6-9 microns above the guide pads and about 15 microns below at the back ... I would say this is a very truthful and informative video
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I felt like I was watching the fundamentals of a GD&T class. Good stuff with great illustrations of principles.
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This was great! I love details of precision machinery, the science of metrology and ideas of quantum mechanics. You combined them all. Very well done. This channel and "Machine Thinking" go very well together.
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I love your approach to these videos how you start at the fundamentals and end with the limit. Very thorough!
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I just found you in my suggestions after watching a bunch of space videos and I'm glad you did. I love the information and how in-depth you go. Thank you for making all these videos, they are really interesting. You earned a new subscriber.
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A few videos later, you have convinced me to subscribe! Keep up the great work!
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Great video! I'm glad these are showing up in my recommended. These videos make a great compliment to the Machine Thinking channel. FIM (full indicator movement) is slowly replacing TIR on engineering drawings. I would've liked to see discussion of roundness vs cylindricity vs sphericity. Roundness has a somewhat transcendent quality because it only exists in 2 dimensions and doesn't exist in a 3D world.
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Your metrology video's are great. Really clear and concise.
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My new fav channel! Keep up the amazing content, you’ll blow up in no time.
