10/01/2009 - 11/01/2009 - Mechanical engineering
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Tuesday, October 27, 2009

THE MICROMETER

The micrometer is a precision measuring instrument, used by engineers. Each revolution of the rachet moves the spindle face 0.5mm towards the anvil face. The object to be measured is placed between the anvil face and the spindle face. The rachet is turned clockwise until the object is ‘trapped’ between these two surfaces and the rachet makes a ‘clicking’ noise. This means that the rachet cannot be tightened any more and the measurement can be read.

















EXAMPLE MEASURE READINGS

Using the first example seen below:

1. Read the scale on the sleeve. The example clearly shows12 mm divisions.

2. Still reading the scale on the sleeve, a further ½ mm (0.5) measurement can be seen on the bottom half of the scale. The measurement now reads 12.5mm.

3. Finally, the thimble scale shows 16 full divisions (these are hundredths of a mm).

The final measurement is 12.5mm + 0.16mm = 12.66


Example :














Ex#2

Read the following 17 micrometer measures. Label your answers with the appropriate units.

Metric Micrometer Readings




























American Standard Micrometer Readings





Solution:

Metric: American:
1. 14.10 mm 1. 0.230 in
2. 10.14 mm 2. 0.364 in
3. 15.29 mm 3. 0.554 in
4. 24.25 mm 4. 0.635 in
5. 18.43 mm 5. 0.608 in
6. 13.18 mm 6. 0.323 in
7. 10.14 mm 7. 0.459 in
8. 13.03 mm 8. 0.803 in
9. 22.18 mm


THE VERNIER CALIPIER

The Vernier Caliper is a precision instrument that can be used to measure internal and external distances extremely accurately. The example shown below is a manual caliper. Measurements are interpreted from the scale by the user. This is more difficult than using a digital vernier caliper which has an LCD digital display on which the reading appears. The manual version has both an imperial and metric scale.
Manually operated vernier calipers can still be bought and remain popular because they are much cheaper than the digital version. Also, the digital version requires a small battery whereas the manual version does not need any power source.




HOW TO READ A MEASUREMENT FROM THE SCALES


EXAMPLE 1: The external measurement (diameter) of a round section piece of steel is measured using a vernier caliper, metric scale.

A. The main metric scale is read first and this shows that there are 13 whole divisions before the 0 on the hundredths scale. Therefore, the first number is 13.
B. The’ hundredths of mm’ scale is then read. Only one division on the main metric scale lines up with a division on the hundredths scale below it, whilst others do not. In the example below, the 41st division on the hundredths scale lines up exactly with a division on the metric scale above.
C. This 41 is multiplied by 0.02 giving 0.82 as the answer (each division on the hundredths scale is equivalent to 0.02mm).
D. The 13 and the 0.82 are added together to give the final measurement of 13.82mm (the diameter of the piece of round section stee)l.







useful link :
http://www.physics.smu.edu/~scalise/apparatus/caliper/tutorial/simulation.html





Saturday, October 24, 2009

describes the common machines used in metal cutting.

describes the common machines used in metal cutting.

arbor The bar attached to the spindle in a horizontal milling machine. The arbor holds the milling cutter.
automatic bar machine A turning machine that continuously cuts a number of parts from a piece of bar stock, one after another. The bar stock advances through the spindle and is held by the collet during the operation.
axis An imaginary straight line that passes through the center of an object.
backstroke The return motion of a saw blade that cuts with a back-and-forth movement.
band saw A long, continuous cutting blade with serrated teeth that is looped around two or more wheels.
bar stock Raw material purchased from metal manufacturers in the form of long bars.
base The foundation of a machine that supports all the other machine components.
bed The main supporting structure upon which the operating parts of the machine are mounted and guided.
bed-type milling machine A type of milling machine used to mill flat surfaces that has a large bed, which only moves along a horizontal axis.
broach A multi-point cutting tool made of a series of progressively smaller teeth that can both remove metal and finish the surface of a workpiece with one pass of the cutting tool.
broaching machine A machine that uses a multi-point cutting tool to shape and finish either the interior of a hole or the surface of a workpiece.
carbide insert A cutting bit made of hard material that has multiple cutting edges. Once a cutting edge is excessively worn, it can be indexed to another edge, or the insert can be replaced.
carriage The section of the lathe that slides back and forth along the ways and supports the cross-slide and cutting tool.
center The device located in the tailstock that holds in place the end of the workpiece opposite the spindle.
chip An unwanted piece of metal that is removed from a workpiece. Chips are formed when a tool cuts or grinds metal.
chuck A device that holds a workpiece in place as it rotates. The chuck commonly has three or four jaws that can be adjusted to fit various sizes.
circular saw A power saw that cuts with a toothed or abrasive disk rotating at high speed.
CNC machining center A sophisticated CNC machine that can perform multiple machining operations in the same setup with a variety of tools.
CNC turning center A sophisticated CNC machine that specializes in turning, boring, drilling, and threading operations, all at the same location.
collet A slitted device that holds a workpiece in place as it rotates. A collet has a hole through which the workpiece passes, and it is designed to hold specific dimensions. Collets can also be used to hold cutting tools.
column The vertical support, or backbone, of a machine.
column-and-knee milling machine A milling machine with a spindle that is mounted in the column and a worktable that rests on an adjustable knee.
compound rest The part of the lathe on the carriage that allows for angular adjustment of the cutting tool.
contour A cutting process that creates a curved, non-linear dimension.
countersinking The cutting of a beveled edge at the end of a hole so that the head of a screw can rest flush with the workpiece surface.
cutting The use of single- or multi- point tools to separate metal from a workpiece in the form of chips.
drilling The use of a rotating drill in order to cut a round hole into a workpiece.
drive The main device that powers the rotation of the spindle.
end mill A thin, tall mill cutter with cutting edges that wind up the sides. Both the bottom and side of the end mill are used during milling operations. End mills resemble drills.
engine lathe The original and most basic type of lathe.
face mill A flat mill cutter with multiple cutting teeth surrounding the tool. The bottom of the face mill is primarily used during milling operations.
feed handle A handle attached to a machine that controls the movement of the cutting tool.
finishing tool A single-point cutting tool used to make a very light cut for final touches to achieve precise tolerances or improved finishes.
form mill A type of milling cutter that is designed in an irregular shape in order to mill contours.
hacksaw A saw that contains a blade made of high-speed steel, molybdenum, or tungsten alloy steel that cuts in one direction.
head The part of a drill press that contains the spindle and the motor.
headstock The end of a lathe that holds the spindle and the drive that rotates the workpiece.
high-speed steel A material used in cutting tools to machine metals at high cutting speeds. High-speed steel stays hard at high temperatures, has great hardness, and is resistant to abrasion.
keyway A rectangular slot or groove that is machined down the length of a hole.
knee The device supported by an elevating screw that raises and lowers and guides the back and forth motion of the saddle.
lathe A machine tool that holds a cylindrical workpiece at one or both ends and rotates it while various cutting tools remove material. Turning is a common operation performed on the lathe.
leadscrew The long, threaded device that controls the precise movement of the carriage on a lathe.
machine tool A power-driven machine that holds a variety of tools. These tools include cutting tools, workholding devices, punches, and other manufacturing tools.
machining The process of removing metal to form or finish a part, either with traditional methods like turning, drilling, milling, and grinding, or with less traditional methods that use electricity, heat, or chemical reaction.
mill A multi-point cutting tool that is used to remove metal from the surface of a workpiece.
milling cutter A rotary cutting tool with teeth around its periphery that is used on milling machines.
milling machine A machine that uses a multi-point tool to remove metal from the surface of a workpiece.
multiple spindle drill A drilling machine that contains two or more spindles, which perform multiple cutting operations at the same time.
multi-point tool A cutting tool that has two or more cutting edges.
overarm The device on a horizontal milling machine that reaches over the workpiece and supports the spindle or arbor.
plain mill A cutting tool for the milling machine with cutting surfaces on the periphery. It is used to mill flat surfaces.
planer-type milling machine A very large type of milling machine that often contains numerous milling heads.
plate stock A flat piece of raw material that is used to make manufactured parts.
pocket An interior recess that is cut into the surface of a workpiece.
radial drill A drilling machine that can accommodate large workpieces by maneuvering an overarm in place over the workpiece.
reaming The use of a multi-point cutting tool to smooth or enlarge a previously drilled hole.
reciprocating The back-and-forth motion of a hacksaw in which only one motion actually contacts and cuts the workpiece.
rough cutting The quick removal of metal from a workpiece without regard to tolerances or finish.
roughing tool A single-point cutting tool used to make very heavy cuts and remove metal as quickly as possible.
saddle The device supported by the knee that slides back and forth on the knee and guides the left and right motion of the worktable.
saw A multi-point cutting device that is used to rough cut a part to a certain length.
shell mill A type of milling cutter that has cutting edges around its periphery and can be mounted on an arbor.
side mill A narrow type of milling cutter that has cutting edges on both its end and periphery.
single-point tool A cutting tool that has a single cutting edge.
slab broach A flat-shaped broach that is used to remove metal from the workpiece surface.
spindle The part of the machine tool that spins. On the mill, the spindle holds a cutting tool. On the lathe, the spindle holds the workpiece.
stock The raw material out of which manufactured parts are made.
tailstock The part located at the end of a lathe opposite the headstock that supports the end of longer workpieces.
tapping The process of cutting internal threads in a workpiece with a multi-point tool.
tolerance The unwanted but acceptable deviation from the desired dimension.
t-slot cutter A type of milling cutter that is used to machine a portion of a T-shaped slot into a workpiece.
turning A machining operation used to make cylindrical parts. A single-point cutting tool passes along the outer surface of a cylindrical workpiece as it rotates, and gradually removes a layer of material.
turret The component of a lathe that holds a number of cutting tools. The turret rotates to place tools in the cutting position.
turret lathe A lathe with a mounted device that holds multiple cutting tools. The turret rotates to position a specific cutting tool in place.
vise A workholding device with one fixed jaw and one moveable jaw. Vises are often used to hold simple rectangular or cubic workpieces on a mill or machining center.
ways Two precisely measured, parallel tracks that support and guide the movement of the carriage and cross slide.
workpiece A part that is being worked on. It may be subject to cutting, welding, forming or other operations.
worktable The part of a machine tool that supports the workpiece and any workholding devices.


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