The Science Of Small Distances

in 2010 an unprecedented milestone of the post-industrial world occurred the total vehicles on earth superseded the 1 billion more even more astounding in 2018 it is estimated that 2.5 to 3 billion internal combustion engines exist on earth the average age of the 250 million vehicles in the United States is 11 and a half years depending on the vehicle and the driving conditions that eleven and a half year old engine could have seen anywhere from 500 million to 1 billion revolutions in its life but how can a machine rotate so reliably for years without failure most of us are intuitively familiar with the roller element bearing a mechanical device that carries a rotating load on a rolling element such as a ball bearing or rollers we see them daily on virtually every single wheel we use as well as various other not so common places but car engines do not rotate on ball bearings or rollers their impressive reliability comes from a remarkably simple bearing device the modern journal bearing ground and polished metal parts are rotated in a hole lined with a replaceable ring of softer contact metal both metals have a low coefficient of friction between them but the incredible efficiency of this design comes from between the metals machined into the dimensions of the two rotating parts is an incredibly tiny gap designed to trap a thin film of oil this thin film of trapped oil takes the entire load of the engines power and is responsible for its longevity and reliability this gap that traps oil has given us the modern industrialized world this ability to create mass-produced parts with tight dimensions and efficiency and interchangeability for better or worse has changed our society and the face of this planet let's explore how small these distances are and what they look like in order to make things with any precision we need dimensional units in our modern world we look to the metre as the basis for all distance measurement it took over two millennia to get here the first forms of standardized length measurement was the cubit and the ancient foot archaeologists believe that the Egyptians ancient Indians and Mesopotamians preferred the cubit while the Romans and Greeks preferred the foot a cubit was defined as the length of the forearm while the foot was defined by the human foot the obvious problem with this was that everyone is different and these lengths could vary up to 15% ancient engineering was coarse and loose by modern standards so these variances were easily tolerated they operated with an archaic version of what we now call low tolerances a modern tolerance is an allowable amount of variation of specified dimensions of a machine or part in modern tolerances the allowed range of the used unit is specified instead of the unit itself varying for example a tolerance of plus or minus one millimeter on a 50 millimeter specification allows for the actual measured dimension to be anywhere between 49 millimeters and 51 millimeters as history progressed the definition of distances shifted between various natural objects finally during the Age of Enlightenment we saw the first definition of distance through scientifically derived means the metre was invented though the metre was initially defined as one ten-millionth of the distance from the equator to the North Pole along a meridian through Paris in modern times it has become the definitive standard of length by deriving its definition from a universal constant the modern metre is defined as the length of the path travelled by light in a vacuum in one 299,792,458 of a second even the imperial unit the foot has evolved into a unit purely derived from the metre one modern foot has become 0.3048 meters exactly now that we understand the basis for units of length let's work our way down to the smallest practical mechanical distances we're all familiar with one of these most state measures divided down to one millimeter with the exception of intricate artisan work and some highly specialized processes this seems to be the practical limit for hands only manufacturing and construction our ability for our hands and eyes to work intolerance is lower than this without the aid of positioning tools start becoming difficult this is a micrometer it's a machinist tool used to measure length with high precision this specific one can be set up to measure increments of two point five four microns or a ten thousandth of an inch this will be our tape measure as we delve into smaller distances this is a third of a millimeter and around one quarter to a third of a millimeter we're at the practical limit of what our eyes can distinguish without tools at this length hand guided work is still possible with positioning tooling such as jigs and guides or through slow subtractive processes such as sanding or grinding at this tolerance were at the practical limit of working with wood dimensional stability is our first practical consideration of material properties when we work with small distances in the case of wood the expansion and contraction of the material based on the environment makes holding a small tolerance difficult if not impossible we're now entering the realm of thickness this envelope is stamped from a thick stock paper 0.25 millimeters thick most thin sheets of material can be found at these sizes the fine wires that make up Ethernet cables and audio cables are also here at this range of small distances our eyes have a hard time intuitively deducing size these are ranges more easily recognized by touch machine tools such as mills lathes and drill presses are a requirement in order to work with these distances working at the 0.25 millimeter size range and tolerances the concept of engineering fit begins to emerge let's say a hypothetical part pair calls for a twenty four point nine eight millimeter cylinder to be fitted into a 25 millimeter hole on paper this makes sense but in real life there are other factors at play to begin with the machine making the part can never truly be perfect it has a tolerance for its accuracy in our example let's assign the machine making our parts a realistic tolerance of plus or minus 25 microns what this means is that no matter how hard we try it's possible that the produced part could be a 25 point zero zero five millimeter cylinder and a twenty four point nine 75 millimeter hole or any other size mismatch within that tolerance that results in poor fitment because of the tolerance of the machine making parts that fit become a lucky but let's say we are able to get a perfect 24 point nine eight millimeter cylinder and a 25 millimeter hole we now encounter a new problem assembly on paper that shouldn't be a problem just slide the part in but if you compare real-life to paper it quickly becomes obvious that to fit these parts together they have to approach each other in a perfectly aligned manner it would be virtually impossible to do this in real life with just our hands making use of positioning tooling may help but at the increase of cost complexity and time of assembly engineers solve both of these problems by introducing the concept of a fit clearance if we take into account the purpose of the parts fitment a purposeful gap between components can be designed in to both accommodate for manufacturing inaccuracies as well as assembly fitting parts together can be categorized into three types a clarence fit location fit and an interference fit in a clearance fit a significant gap is created between parts this may be done to aid in manufacturing and assembly this is often found in parts that are inexpensive non-critical designed for tactile use or require simple motion such as with simple slides or rollers many of the components we interact with daily such as buttons switches knobs and other tactile controls operate with clearance fits in the 0.25 millimeter range in a location fit a very tight gap is created mostly to accommodate for manufacturing inaccuracies it's usually used for precision part fitment and generally requires tooling or force to aid in alignment and assembly an interference fit is a unique circumstance in which a smaller part is stretched with heat or tooling in order to force a larger part into it this is generally done to pin parts together with friction and can be very effective in areas where other means of component fastening aren't available in general engineers choose fit and clearance specifications by balancing the requirements of part functions manufacturing costs material properties assembly costs and serviceability often the feel of quality or cheapness of a product we use can be directly attributed to the choices made in this juggling act this is about 25 microns the next step in our journey we are now in the realm of machine only processes how small is 25 microns this thin razor blade is approximately 4 times thicker this is the tolerance in which simple machines exist firearms quality hand tools lower end machine tools and less critical automotive parts can all be found here coincidentally this is also the rough size of the popular standard of small sizes the thickness of a human here as we approach the 25 micron mark we enter the realm of precision fit at around one tenth of a millimeter assembly by human hands only becomes difficult below this tolerance a combination of extreme care tooling and force may be required we can't directly see or feel changes at distances this small so measurement tools are a must at these tolerances the effects of temperature on materials require consideration for example a 25 millimeter aluminum rod cut at a length of 100 millimetres at room temperature will expand up to 51 microns when heated to a hundred degrees an aluminum part machined on a cold day may come out of specification on a hot day and even more extreme but more common example of this as a car engine modern engines are composed mostly of aluminum and can have temperature swings from bitter sub-zero winter temperatures all the way to it's 100 degree operating temperature engineers take this into account when choosing clearances as well as designing around expansion in general let's take a look at thermal expansion in practice this is an engine piston it channels the force of philia combustion into rotational energy connecting it to the rest of the engine is this steel cylinder called a wrist pin at room temperature fitting the wrist pin into the piston is almost impossible due to an extremely tight clearance but if we warm up the aluminum piston to 65 degrees the hole in the piston expands to the point where the wrist pain can easily be inserted by hand moving in order of magnitude down we enter the realm of the micron this is the practical limit of general machining at these tolerances not only does part temperature have to be taken into account but even the operating temperature of the equipment used to create the part needs to be considered often grinding a surface slowly is needed to hit tolerances this low but what does a micron look like well we're in the realm of surface textures now this is three microns a size roughly similar to a tiny silk particle to put this into perspective 1200 grit sandpaper a great used in polishing that has a surface roughness similar to leather protrudes a little more than 2.5 microns the red blood cells that run through our veins and arteries are six to eight microns just the act of holding a piece of aluminum in your hand can expand it with body heat more than twenty microns astoundingly a micron is only about 10,000 atoms of distance components holding tolerances down to two to three microns are typically reserved for precision machinery machine tools tooling and jigs instrumentation and are prevalent in engine components in many machines including engines clearance gaps in the 2 to 5 micron tolerance range are used exclusively for maintaining consistent oil films for use as liquid bearings the tolerance of this gap is absolutely critical to creating proper oil film strength for the oils viscosity these miniscule gaps allow years of engine life with minimal actual metal to metal contact within an engine directly machining lengths even smaller than a few microns are possible but a reserved for a highly specialized machinery usually designed for instrumentation or science working at these scales we begin transitioning in to processes such as photolithography nanotechnology and other submicron processes that are beyond the scope of this video with current semiconductor manufacturing technology expected to push distances of 5 nanometers by 2020 at this level of small we are literally dealing with distances 50 atoms wide you

Channel: New Mind

Views: 1,161,205

Rating: 4.9226704 out of 5

Keywords: small measurements, millimeter, microns, how small is an atom, milling, cnc milling, metrology and measurement, metrology basics, metrology technician, dial indicator, micrometer reading, measurement of small length, feeler gauge, machining, grinding, manufacturing engineering, manufacturing science, engineering videos, engineering science, tolerance, clearance fit, interference fit, location fit, fit clearance and tolerance, thermal expansion, journal bearing, engine design

Id: Aw-xbs8ZWxE

Length: 13min 31sec (811 seconds)

Published: Thu Dec 19 2019

Reddit Comments

[u/giddyup05]

That was super cool. Very informative.