The Science Of Roundness

every year in the United States we collectively drive about three and a half trillion miles every single one of those miles are made possible by the hundreds of rotating parts than enable a vehicle to drive down the road roller bearings ball bearings journals shafts gears pulleys and sprockets are all descendants of the wheel the wheel is often praised as man's first invention but it's actually an emergent device conceived of an idea much more profound and integral to the evolution of civilization let's say we wanted to lift a thousand pound rock but at best we're only able to generate 200 pounds of force if we take a pole and position it over a pivot point or a fulcrum so that the side we apply force to it's five times longer than the lifting side we can now lift our rod this simple idea is the basis of mankind's first simple machine the lever known as mechanical advantage or leverage the lever allows us to trade distance of travel for force if we take the fulcrum point of our lever and move it completely over to one end duplicate it repeatedly with each copy sharing the same fulcrum a new simple machine is formed the wheel wheels allow us to multiply distance speed or force based on how much leverage we put on there Center Point a wheel usually mounts to a shaft at its center called an axle if the axle is fixed to the wheel rotational force known as torque can be transmitted to or from the wheel much like a lever if we make the wheel larger in diameter we can create more torque at its center point at the cost of having the outer edge of the wheel traversing a longer distance conversely if we apply the torque at the center point the wheel diameter determines how much distance the wheel can travel forward in one rotation if we link two wheels together by a belt chain or a force transmitting feature such as teeth we create a pulley sprocket or here linking wheels together allow us to multiply torque to a rotational speed and vice versa in predetermined ratios in this example wheel a is twice the diameter if will be they're linked in a two-to-one ratio in order to rotate wheel a once we need to rotate will be twice this doubles the torque at wheel B's axle at the cost of requiring two rotations in the opposite direction it only takes half a turn of wheel ade to make wheel B rotate once the torque applied is half but it rotates faster machines that link wheels together for the purposes of converting between torque and speed are sometimes called gearboxes or transmissions wheels provide another characteristic that has been critical to industrial growth if we look at an example of a perfect wheel rolling down the road the forces that are transmitted between the wheel and the road transmitted at one point the majority of the wheel circumference never make contact with the road this characteristic of reducing material contact to a small area allows wheels to operate as friction reducing elements this characteristic forms the basis for bearings in order for wheels and their modern industrial analogues to perform effectively and reliably especially at higher speeds smooth rotation with exacting dimensional control is key pushing forward this constant reinvention of the wheel in order to advance modern industry is the science of roundness [Music] you [Music] roundness along with the size play critical roles and 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 in order to measure roundness we need to quantify what roundness actually is if we look at a perfectly round circle and try to determine what makes it perfectly round we observe that it maintains the same diameter no matter how we measure it it has a constant diameter but this doesn't constitute roundness reuleaux polygons are a group of curvilinear polygons built up of circular arcs that have constant diameters but are by all intuitive means not round constant diameter is a prerequisite to roundness but it's not an indicator from this let's look at a perfect circle and another constant diameter shape and determine what makes one more round than the other if we first draw a circle that fully encompasses the entire shape we have what's known as a circumscribed circle for the perfectly round circle this is the circle itself next we draw the largest circle that can be contained by the shape this is known as an inscribed circle for the perfectly round circle this is again the circle itself from the overlaid circles we observe that roundness is defined by the relationship between the circumscribed circle and the inscribed circle a perfectly round circle has no difference between the two overlay circles as a shape become less round the diameter difference between both overlay circles become larger it should be noted that the technical definition of roundness describes overall shape and is not based on the radial distance from a common center point rollers and ball bearings are examples of roundness with no defined center point however in practice roundness relative to center access is required both in engineering requirements and for the purposes of measurement gears pulleys sprockets wheels and other force transmitting rotating assemblies are generally designed around the center axis the ability to verify the roundness of a part is absolutely critical to a components performance these components often function with friction and vibration in mind as systemic failure of moving components can occur if specifications aren't met measuring apart around this can be classified into two categories of measurement methods intrinsic datum reference and extrinsic datum reference a datum reference or datum is an important feature of a part such as a point line plane whole set of holes or pair of surfaces datum serve as a reference in defining the geometry of a part and are used in measuring the geometry datums can be used to determine how closely a part matches a specified value in the intrinsic data method the datum points used for measurement are directly taken off the part and its contact points with a reference surface typically a flat surface is used for a single datum measurement or AV block for a two data 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 zero to a start point as the part is rotated deviations from roundness displaces the measurement tool found the zero with surface Peaks creating positive displacement and valleys negative ones a perfectly round part will never displace the measurement tool throughout a full rotation on parts that are not round the measured difference between the lowest surface Valley and the highest surface peak through outer rotation is known as its total indicated run out or run out run out as a simple indicator of a parts rawness it's often used as a quality check to verify a parts usability but may not indicate how a part will function or provide any useful information for the purposes of refining manufacturing of the part run-out checks are often specified in the servicing of rotating machines such as engines tools and mechanical power transmission assemblies they provide a simple go no-go test for the in fuel servicing of components what do run-outs feel like in practice simple hand use items such as doorknobs and rolling pins usually have large run outs in the 1/32 of an inch to one eighth of an inch range cheap power tools and lower quality general use parts have rotating component run outs in the hundredths of an inch range more precise components such as engine crank shafts typically have run-out specs for their journals at a thousandth of an inch or less on machine tools critical rotating assembly run-outs approach one ten thousandth of an inch even more astonishing some of the most round mass-produced components grade three ball bearings have a sphericity a three-dimensional analogue of roundness of three millionths of an inch this is a displacement equivalent to about 750 hydrogen atoms if a one-inch grade three ball bearing was scaled up to the size of the earth the difference between the deepest depth of the ocean and the tallest mountain peak would only be 125 feet the intrinsic data method while relatively easier to accomplish suffers from certain limitations it's setup can be difficult as it relies on reference surfaces using a single datum surface can create issues with mounting and positioning and the two data method can be problematic if appropriate v angles aren't used even more limiting is the difficulty in measuring wrong parts with surface features or larger deformations for example if we attempt to measure the roundness of aid gear the depth spacing and shape of its teeth present an obstacle to measuring its true roundness its measured run-out stops reflecting the part roundness and becomes a false measurement based on its surface features in addition this method offers no means of testing roundness relative to an axis of rotation the solutions to the limitations of the intrinsic data method is extrinsic data measurement extrinsic data measurement is done by assigning a rotational axis datum to the part and aligning it to the circular datum of a highly accurate rotating measuring fixture this is often a table mounted to a spindle that allows for centering and leveling of the part during rotation a transducer measures radial variations on the surface of the part with respect to the spindles axis limited only by the precision of the spindle and transducer gauge head the extrinsic data method can be used for the most extreme roundness specifications and parts with complex surface features it is also suitable for both internal and external roundness measurement due to the flexibility of the fixturing the method in which measurement data is processed from the extrinsic data method offers more insight into the parts performance and can help aid in refining manufacturing the resultant data is represented as radial variations on a polar graph this graph is then used to calculate a reference circle and its deviation from reference roundness the least square reference circle the most commonly used reference circle is a circle that equally divides the area between the inside and outside of the reference circle out of wrongness is then presented in terms of the maximum displacement from the reference circle the difference between the highest peak to the lowest Valley a minimum zone reference circle is derived by first calculating the smallest circle that can fit inside of the measured data next the smallest circle that can encompass the measured data is calculated the out of roundness is given by the radial separation between these two circles that enclose the data a minimum circumscribed reference circle sometimes known as the ring gauge reference circle 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 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 are known as undulations an example of this is oval tee which indicates an irregularity that occurs two times in one complete revolution the part has two lobes or two undulations per revolution and even or odd number of lobes may be present on a part contributing to a problem of fit with meeting parts high order lobing often caused by tooling chatter vibration and processing marks are generally more important to the function than to the fit of a part by filtering the frequency of undulations per revolution in the measured data the properties of these harmonics can be analyzed instrument and workpiece setup may contribute to low frequency harmonics while machining and process effects as well as material rigidity may contribute to higher frequency harmonic effects in 2011 the international community 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 aim 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 it's volume determined for this to work effectively the ball had to be ground as accurately as possible and thus the world's roundest object was created after months of polishing the team produced two spheres with a diameter of 93 0.75 millimeters the small-scale roughness of the balls varies by only a third of a nanometer or two silicon atoms and the run out of only 60 to 70 nanometers or about 300 silicon atoms a human licensure an optical engineer on the project has stated if you were to blow up our spheres to the size of the earth you would see a small ripple in the smoothness of about 12 to 15 millimeters and the variation of only 3 to 5 meters in the roundness 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 scientists at Harvard were able to measure the smallest roundness ever the roundness of charge distribution was so many skill that if the electron were a sphere the size of the earth the out of roundness of this data would be the equivalent to shaving less than 2 nanometers or about 20 hydrogen atoms off the North Pole and pasting it onto the South Pole at this scale we're at the limits of what we can consider tangible around us at the subatomic level objects become intuitively sizeless and our measurements become statistical data representing the distribution of subatomic properties you

Channel: New Mind

Views: 212,034

Rating: 4.8564553 out of 5

Keywords: roundest object, roundness, science of roundness, runout jig, total indicator runout, how wheels work, round objects, how bearings work, ball bearings, roller bearing vs ball bearing, datum, roundess measurement, history of the wheel and axle, history of the wheel, camshaft journal, crankshaft journal measurement, avogadro project, roundest ball, how to measure roundness, grade 3 ball bearing, polishing ball bearings, tool chatter, new mind, v-block, interesting, explanier

Id: NjbvOTUSqdI

Length: 17min 1sec (1021 seconds)

Published: Fri Jan 11 2019

Reddit Comments

[u/llothar]

This is the best material on the topic I encountered. It gives a nice overview of the issue. Main thing missing is the ASME/ISO differences, because these are at the core of the definition (ASME diameter is the limits between the maximum inscribed and minimum superscribed, ISO is the two point calliper like measurement)

[u/ImNeworsomething]

Would love to see more videos like these on metrology/GD&T type stuff

[u/stoopslife]

Cool video but tough to get through due to monotone, steady paced voice. It is difficult to distinguish important information from sentence filler.

[u/large-farva]

Watch video of 1.5x ot 1.75x speed.

[u/ahandmadegrin]

I love that the natural roundness at the atomic level is near perfect. It's awe inspiring.

[u/thukon]

Great video. Someone correct me if Im wrong but is a V-block runout check really an indicator of Total Indicated Runout? I think the datum axis needs to be fixed right? It would really be an indicator of just circularity.

[u/MjrK]

At about 12:45, when describing the minimum-zone reference circle method, the video depicts a circumscribed circle, but it only has 2 contact points with the measured object. However, for any minimum-circle of 2 points, the line between those points must be the diameter of that minimum-circle.

I understand it's just an illustration, but it just looked so silly to me at a first glance.