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From Wikipedia

Screw thread

A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread. More screw threads are produced each year than any other machine element.

The mechanical advantage of a screw thread depends on its lead, which is the linear distance the screw travels in one revolution. In most applications, the lead of a screw thread is chosen so that friction is sufficient to prevent linear motion being converted to rotary, that is so the screw does not slip even when linear force is applied so long as no external rotational force is present. This characteristic is essential to the vast majority of its uses. The tightening of a fastener's screw thread is comparable to driving a wedge into a gap until it sticks fast through friction and slight plastic deformation.

Applications

Screw threads have several applications:

  • Fastening
  • Moving objects linearly by converting rotary motion to linear motion, as in the leadscrew of a jack.
  • Measuring by correlating linear motion to rotary motion (and simultaneously amplifying it), as in a micrometer.
  • Both moving objects linearly and simultaneously measuring the movement, combining the two aforementioned functions, as in a leadscrew of a lathe.

In all of these applications, the screw thread has two main functions:

  • It converts rotary motion into linear motion.
  • It prevents linear motion without the corresponding rotation.

Design

Gender

Every matched pair of threads, external and internal, can be described as male and female. For example, a screw has male threads, while its matching hole (whether in nut or substrate) has female threads. This property is called gender.

Handedness

The helix of a thread can twist in two possible directions, which is known as handedness. Most threads are oriented so that a bolt or nut, seen from above, is tightened (the item turned moves away from the viewer) by turning it in a clockwise direction, and loosened (the item moves towards the viewer) by turning anti-clockwise. This is known as a right-handed (RH) thread, because it follows the right hand grip rule (often called, more ambiguously, "the right-hand rule"). Threads oriented in the opposite direction are known as left-handed (LH).

To determine if a particular thread is right or left-handed, look straight at the thread. If the helix of the thread is moving up to the right, it is a right-handed thread and conversely up to the left, a left-handed thread. This holds whether the thread is oriented up or down.

By common convention, right-handedness is the default handedness for screw threads. Therefore, most threaded parts and fasteners have right-handed threads. Left-handed thread applications include:

  • Where the rotation of a shaft would cause a conventional right-handed nut to loosen rather than to tighten due to fretting induced precession. Examples include:
  • In some gas supply connections to prevent dangerous misconnections, for example in gas welding the flammable gas supply uses left-handed threads.
  • In a situation where neither threaded pipe end can be rotated to tighten/loosen the joint, e.g. in traditional heating pipes running through multiple rooms in a building. In such a case, the coupling will have one right-handed and one left-handed thread
  • In some instances, for example early ballpoint pens, to provide a "secret" method of disassembly.
  • In mechanisms to give a more intuitive action as:
    • The leadscrew of the cross slide of a lathe to cause the cross slide to move away from the operator when the leadscrew is turned clockwise.
    • The depth of cut screw of a "Stanley" type metal plane (tool) for the blade to move in the direction of a regulating right hand finger.

The term chiralitycomes from the Greek word for "hand" and concerns handedness in many other contexts.

Form

The cross-sectional shape of a thread is often called its form or threadform (also spelled thread form). It may be square, triangular, trapezoidal, or other shapes. The terms form and threadform sometimes refer to all design aspects taken together (cross-sectional shape, pitch, and diameters).

Most triangular threadforms are based on an isosceles triangle. These are usually called V-threads or vee-threads because of the shape of the letter V. For 60° V-threads, the isosceles triangle is, more specifically, equilateral. For

Rain gauge

A rain gauge (also known as a udometer or a pluviometer [Pluviograph ] or an ombrometer or a cup) is a type of instrument used by meteorologists and hydrologists to gather and measure the amount of liquid precipitation (solid precipitation is measured by a snow gauge) over a set period of time.

History

The first known records of rainfalls were kept by the Ancient Greeks about 500 B.C. This was followed 100 years later by people in India using bowls to record the rainfall. The readings from these were correlated against expected growth, and used as a basis for land taxes. In the Arthashastra, used for example in Magadha, precise standards were set as to grain production. Each of the state storehouses were equipped with a standardised rain gauge to classify land for taxation purposes.

While some sources state that the much later cheugugi of Korea was the world's first gauge, other sources say that Jang Yeong-sil developed or refined an existing gauge. In 1662, Christopher Wren created the first tipping-bucket rain gauge in Britain.

Principles

Most rain gauges generally measure the precipitation in millimeters. The level of rainfall is sometimes reported as inches or centimeters.

Rain gauge amounts are read either manually or by AWS (Automatic Weather Station). The frequency of readings will depend on the requirements of the collection agency. Some countries will supplement the paid weather observer with a network of volunteers to obtain precipitation data (and other types of weather) for sparsely populated areas.

In most cases the precipitation is not retained, however some stations do submit rainfall (and snowfall) for testing, which is done to obtain levels of pollutants.

Rain gauges have their limitations. Attempting to collect rain data in a hurricane can be nearly impossible and unreliable (even if the equipment survives) due to wind extremes. Also, rain gauges only indicate rainfall in a localized area. For virtually any gauge, drops will stick to the sides or funnel of the collecting device, such that amounts are very slightly underestimated, and those of .01 inches or .25 mm may be recorded as a trace.

Another problem encountered is when the temperature is close to or below freezing. Rain may fall on the funnel and freeze or snow may collect in the gauge and not permit any subsequent rain to pass through.

Rain gauges should be placed in an open area where there are no obstructions, such as building or trees, to block the rain. This is also to prevent the water collected on the roofs of buildings or the leaves of trees from dripping into the rain gauge after a rain, resulting in inaccurate readings.

Types

Types of rain gauges include graduated cylinders, weighing gauges, tipping bucket gauges, and simple buried pit collectors. Each type has its advantages and disadvantages for collecting rain data.

Standard rain gauge

The standard rain gauge, developed around the start of the 20th century, consists of a funnel attached to a graduated cylinder that fits into a larger container. If the water overflows from the graduated cylinder the outside container will catch it. When measurements are taken, the cylinder will be measured and then the excess will be put in another cylinder and measured. In most cases the cylinder is marked in mm and in the picture above will measure up to 25 mm (0.98 in) of rainfall. Each horizontal line on the cylinder is 0.2 mm (0.007 in). The larger container collects any rainfall amounts over 25 mm that flows from a small hole near the top of the cylinder. A metal pipe is attached to the container and can be adjusted to ensure the rain gauge is level. This pipe then fits over a metal rod that has been placed in the ground.

Weighing precipitation gauge

A weighing-type precipitation gauge consists of a storage bin, which is weighed to record the mass. Certain models measure the mass using a pen on a rotating drum, or by using a vibrating wire attached to a data logger. The advantages of this type of gauge over tipping buckets are that it does not underestimate intense rain, and it can measure other forms of precipitation, including rain, hail and snow. These gauges are, however, more expensive and require more maintenance than tipping bucket gauges.

The weighing-type recording gauge may also contain a device to measure the quantity of chemicals contained in the location's atmosphere. This is extremely helpful for scientists studying the effects of greenhouse gases released into the atmosphere and their effects on the levels of the acid rain.

Tipping bucket rain gauge

The tipping bucket rain gauge consists of a funnel that collects and channels the precipitation into a small seesaw-like container. After an amount of precipitation equal to 0.2 mm (0.007 in) falls, the lever tips, dumping the collected water and sending an electrical signal. The recorder consists of a pen mounted on an arm attached to a geared wheel that moves once with each signal sent from the collector. When the wheel turns the pen arm moves either up or down leaving a trace on the graph and at the same time making a loud click. Each jump of the arm is sometimes referred to as a 'click' in reference to the noise. The chart is measured in 10 minute periods (vertical lines) and 0.4 mm (0.015 in) (horizontal lines) and rotates once every 24 hours and is powered by a clockwork motor that must be manually wound.

The tipping bucket rain gauge is not as accurate as the standard rain gauge because the rainfall may stop before the lever has tipped. When the next period of rain begins it may take no more than one or two drops to tip the lever. This would then indicate that 0.2 mm (0.007 in) has fallen when in fact only a minute amount has. Tipping buckets also tend to underestimate the amount of rainfall, particularly in snowfall and heavy rainfall events.. The advantage of the tipping bucket rain gauge is that the character of the rain (light, medium or heavy) may be easily obtained. Rainfall character is decided by the total amount of rain that has fallen in a set period (usually 1 hour) and by counting the number of 'clicks' in a 10 minute period the observer can decide the character of the rain. Correction algorithms can be applied to the data as an accepted method of cor


From Encyclopedia

Pressure Gauge Pressure Gauge

Many of the processes in the modern world involve the measurement and control of pressurized liquid and gas systems. This monitoring reflects certain performance criteria that must be controlled to produce the desirable results of the process and insure its safe operation. Boilers, refineries, water systems, and compressed gas systems are but a few of the many applications for pressure gauges. The mechanical pressure indicating instrument, or gauge, consists of an elastic pressure element; a threaded connection means called the "socket"; a sector and pinion gear mechanism called the "movement"; and the protective case, dial, and viewing lens assembly. The elastic pressure element is the member that actually displaces or moves due to the influence of pressure. When properly designed, this pressure element is both highly accurate and repeatable. The pressure element is connected to the geared "movement" mechanism, which in turn rotates a pointer throughout a graduated dial. It is the pointer's position relative to the graduations that the viewer uses to determine the pressure indication. The most common pressure gauge design was invented by French industrialist Eugene Bourdon in 1849. It utilizes a curved tube design as the pressure sensing element. A less common pressure element design is the diaphragm or disk type, which is especially sensitive at lower pressures. This article will focus on the Bourdon tube pressure gauge. In a Bourdon tube gauge, a "C" shaped, hollow spring tube is closed and sealed at one end. The opposite end is securely sealed and bonded to the socket, the threaded connection means. When the pressure medium (such as air, oil, or water) enters the tube through the socket, the pressure differential from the inside to the outside causes the tube to move. One can relate this movement to the uncoiling of a hose when pressurized with water, or the party whistle that uncoils when air is blown into it. The direction of this movement is determined by the curvature of the tubing, with the inside radius being slightly shorter than the outside radius. A specific amount of pressure causes the "C" shape to open up, or stretch, a specific distance. When the pressure is removed, the spring nature of the tube material returns the tube to its original shape and the tip to its original position relative to the socket. Pressure gauge tubes are made of many materials, but the common design factor for these materials is the suitability for spring tempering. This tempering is a form of heat treating. It causes the metal to closely retain its original shape while allowing flexing or "elasticity" under load. Nearly all metals have some degree of elasticity, but spring tempering reinforces those desirable characteristics. Beryllium copper, phosphor bronze, and various alloys of steel and stainless steel all make excellent Bourdon tubes. The type of material chosen depends upon its corrosion properties with regards to the process media (water, air, oil, etc). Steel has a limited service life due to corrosion but is adequate for oil; stainless steel alloys add cost if specific corrosion resistance is not required; and beryllium copper is usually reserved for high pressure applications. Most gauges intended for general use of air, light oil, or water utilize phosphor bronze. The pressure range of the tubes is determined by the tubing wall thickness and the radius of the curvature. Instrument designers must use precise design and material selection, because exceeding the elastic limit will destroy the tube and accuracy will be lost. The socket is usually made of brass, steel, or stainless steel. Lightweight gauges sometimes use aluminum, but this material has limited pressure service and is difficult to join to the Bourdon tube by soldering or brazing. Extrusions and rolled bar stock shapes are most commonly used. The movement mechanism is made of glass filled polycarbonate, brass, nickel silver, or stainless steel. Whichever material is used, it must be stable and allow for a friction-free assembly. Brass and combinations of brass and polycarbonate are most popular. To protect the Bourdon tube and movement, the assembly is enclosed within a case and viewing lens. A dial and pointer, which are used to provide the viewer with the pressure indication, are made from nearly all basic metals, glass, and plastics. Aluminum, brass, and steel as well as polycarbonate and polypropylene make excellent gauge cases and dials. Most lenses are made of polycarbonate or acrylic, which are in favor over glass for obvious safety reasons. For severe service applications, the case is sealed and filled with glycerine or silicone fluid. This fluid cushions the tube and movement against damage from impact and vibration. Calibration occurs just before the final assembly of the gauge to the protective case and lens. The assembly consisting of the socket, tube, and movement is connected to a pressure source with a known "master" gauge. A "master" gauge is simply a high accuracy gauge of known calibration. Adjustments are made in the assembly until the new gauge reflects the same pressure readings as the master. Accuracy requirements of 2 percent difference are common, but some may be 1 percent, .5 percent, or even .25 percent. Selection of the accuracy range is solely dependant upon how important the information desired is in relationship to the control and safety of the process. Most manufacturers use a graduated dial featuring a 270 degree sweep from zero to full range. These dials can be from less than I inch (2.5 centimeters) to 3 feet (.9 meter) in diameter, with the largest typically used for extreme accuracy. By increasing the dial diameter, the circumference around the graduation line is made longer, allowing for many finely divided markings. These large gauges are usually very fragile and used for master purposes only. Masters themselves are inspected for accuracy periodically using dead weight testers, a very accurate hydraulic apparatus that is traceable to the National Bureau of Standards in the United States. It is interesting to note that when the gauge manufacturing business was in its infancy, the theoretical design of the pressure element was still developing. The Bourdon tube was made with very general design parameters, because each tube was pressure tested to determine what range of service it was suitable for. One did not know exactly what pressure range was going to result from the rolling and heat treating process, so these instruments were sorted at calibration for specific application. Today, with the development of computer modeling and many decades of experience, modern Bourdon tubes are precisely rolled to specific dimensions that require little, if any, calibration. Modern calibration can be performed by computers using electronically controlled mechanical adjusters to adjust the components. This unfortunately eliminates the image of the master craftsman sitting at the calibration bench, finely tuning a delicate, watch-like movement to extreme precision. Some instrument repair shops still perform this unique work, and these beautiful pressure gauges stand as equals to the clocks and timepieces created by master craftsmen years ago. Once the calibrated gauge is assembled and packaged, it is distributed to equipment manufacturers, service companies, and testing laboratories for use in many different applications. These varied applications account for the wide range in design of the case and lens enclosure. The socket may enter the case from the back, top, bottom or side. Some dials are illuminated by the luminescent inks used to print the graduations or by tiny lamps connected to an outside electrical source. Gauges intended for high pressure service usually are of "dead front" safety design, a case design feature that places a substantial thickness of case material between the Bourdon tube and the dial. This barrier protects the instrument viewer from gauge fragments should the Bourdon tube rupture due to excess pressure. The internal case design directs these high velocity pieces out the back of the gauge, away from the viewer. Many applicati


From Yahoo Answers

Question:a thin wire is wounded around a pencil.The total length of the wire that wounds the pencil is 2 cm,what is the diameter of the wire?

Answers:2 cm is the circumference (C=pi*OD), and from that value you can calculate the outside diameter which is the sum of the diameter of the pencil and 2x the diameter of the wire (OD= y + 2x where y is the D of pencil an x the D of wire). You can't still solve it because the diameter of the pencil is not given. ;-)

Question:On a Circuit breaker or sub panel terminal lug, how tight do you go when you screw the wire down? Do you "fan" the wires out or let the screw flatten it for you.

Answers:As tight as you can get with your screwdriver. Loose wires are bad. The tighter the better (within reason).

Question:I was wondering how you hook up an Air Pressure Gauge to a potato gun's combustion chamber to see how much pressure is built up in the chamber. (that way i can avoid going to high and blowing the gun up). Do i just need to buy one and then screw it into the PVC pipe or is there a certain procedure and adapter that i need to get an accurate reading. i would like to have a gauge i could hook up to a combustion potato gun (preferably) and a pneumatic gun also, so i could use it for testing purposes. i have NO experience in hooking up pressure gauges so please be as detailed as possible. thank you.

Answers:You could thread it straight into the combustion chamber or give yourself some slack by threading on an extension tube. If you use tubing make sure that it is designed for high pressure or your pressure reading could have substantial loss. Use a gauge that allows the arrow to stick at max pressure since you are measuring a dynamic system. Remember that since you are drilling a hole into the combustion chamber, you are creating a weak spot in the material which could allow material fatigue or failure to occur. You can reinforce the hole with some kind of flexible, PVC compatible glue or use a combustion chamber with adequate thickness. If you are really cheap you can wrap some duct tape around the chamber so that if it does explode shrapnel hopefully won't fly into your face. Since potato guns are illegal in some counties, everything I have written is for entertainment purposes only and should never be attempted by anyone :) .

Question:most screw catalogues use gauge sizes for the size of the screw eg 8 x 1inch but some catologues use the diameter of the screw in mm eg 4.0 x 25mm what is the metric equivalent for a 10 guage x 1inch wood screw?

Answers:5mm x 25 This chart has the metric conversion you asked for, not just the imperial ones as above: http://www.diydoctor.org.uk/projects/screwsize.htm The link is better formated, but the cut 'n' paste below gives you the idea: Metric/Imperial Conversion Chart GaugeLengthImperialGaugeLengthImperial mmmmSizemmmmSize 3124 x 1/23.5126 x 1/2 164 x 5/8166 x 5/8 204 x 3/4206 x 3/4 254 x 1256 x 1 304 x 1 1/4306 x 1 1/4 404 x 1 1/2406 x 1 1/2 4128 x 1/24.5259 x 1 168 x 5/8309 x 1 1/4 208 x 3/4359 x 1 3/8 258 x 1409 x 1 1/2 308 x 1 1/4459 x 1 3/4 358 x 1 3/8509 x 2 408 x 1 1/2609 x 2 3/8 458 x 1 3/4709 x 2 3/4 508 x 2759 x 3 608 x 2 3/8 708 x 2 3/4 52510 x 163012 x 1 1/4 3010 x 1 1/44012 x 1 1/2 3510 x 1 3/85012 x 2 4010 x 1 1/26012 x 2 3/8 4510 x 1 3/47012 x 2 3/4 5010 x 27512 x 3 6010 x 2 3/88012 x 3 1/4 7010 x 2 3/49012 x 3 1/2 7510 x 310012 x 4 8010 x 3 1/411012 x 4 3/8 9010 x 3 1/213012 x 5 1/8 10010 x 415012 x 6

From Youtube

How To: Tapping Screw Threads :How to use a tap to cut or repair internal thread. The full list of part numbers and tools required are available at the website. Visit www.iheartrobotics.com for more robotics news and information.

How to cut an electrical screw or machine screw - ultimate handyman DIY tips :How to cut an electrical screw or machine screw using a pair of electricians pliers. Cutting metric screws this way means that the thread is not damaged and so there is no making good of the thread after cutting. Brought to you by www.ultimatehandyman.co.uk