Watching the long pc;inter on the gage, continue raising the work with the elevating wheel until PLASTICS the long pointer is nearly upright within approximately five divisions, plus or minus, on the scale.
This step of th- procedure sets the minor load. Turn the zero adjuster. Tap the depressor bar downwal-d to release the weights and apply the major load. Watch the pointer until it comes to rest. Turn the crank handle upward and forward, thereby removing the major but not the minor load.
This will leave the penetrator in contact with the specimen but not under pressure. Observe where the pointer now comes to rest and read the Rockwell hardness number on the dial.
If the test has been made with the spheroconical penetrntor and a weight of kilograms, the reading is taken from the black, or C. In the first example the number is prefixed by Rb, in the latter instance by Rc.
Turn the handwheel to lower the anvil. Tlren remove the test specimen. The Brinell hardness testing machine provides a convenient and reliable hardness test. The machine is not suitable, however, for small or thin pieces. This machine has a vertical hydraulic press design and is generally hand operated, a lever being used to apply the load which forces a IO-millimeter diameter hardened steel or tungstencarbide ball into the test specimen.
For ferrous metals, a kilogram load is applied. For nonferrous metals, the load is kilograms. In general, pressure is applied to ferrous metals for 10 seconds, while 30 seconds are required for nonferrous metals. After the pressure has been applied for the appropriate time, the diameter of the depression produced is measured with a microscope having an ocular scale.
The Brine11 hardness number Bhn is the ratio of the load in kilograms to the impressed surface area in square millimeters. The greater the distance, the softer the metal, and the lower the Brine11 hardness number will be. The width of the indentation is measured with a microscope and the hardness number corresponding to this width is found by consulting a chart or table.
The Brine11 hardness machine is of greatest vahle in testing soft and med! The reason is that the fioor is the ba:der of the two surfaces. This is the principle upon which the Scleroscope works. When using the Scleroscope hardness test, a diamond-pointed hammer is dropped through a guiding glass tube onto the test piece and the rebound bounce is checked on a scale.
The harder the metal being tested, the higher the hammer will? The Scleroscope is portable and can be ued to test the hardness of pieces too large to be plxed on the anvil or tables of other machines. So41 pieces do not have the necessary backing and cannot be held rigidly enough to give accurate readings. If large sections are not d, if they are oddly shaped, if they have overhanging sections, or if they are hollow, the rexlings may be in error.
The Vickers test measures hardness by a method similar to that used in the Brine11 test. The indenter, however, is not a ball, hut a square-based diamond pyramid, which makes it accurate for testing thin sheets as well as the hardest steels. Up to an approximate hardness number of , the results of the Vickers and the Brine11 tests are about the same. Above , Brine11 accuracy becomes progressively lower.
This divergence represents a weakness in the Brine11 method; a weakness that is the result of the tendency of the Brine11 indenter ball to flatten under heavy loads. It is for this reason that the Brine11 numbers over are considered to be of doubtful reliability. If a shop has one type of hardness tester and the specifications indicated by the blueprint are for another type, a conversion table, such as Table 2A. Values beyond nwmal range for scale. Plastics are formed from organic materials geriirallv with some form of carbon as their basic element.
Plastics are referred to as synthetic material, but this does not necessarily mean that they are inferior to natural material.
On the contrary, they have been designed to perform particular functions that no natural material can perform. Plastics can be obtained in a varie? Some plastics are as tough, but not so hard as steel; some are as pliable as rubber; some are more transparent thaE glass; and some are : [email protected] iiran aiuminum.
Plastic materials fall into two major divisionsthwmosettings and thermoplastics-and it is necessary, if you are goir:g to perform anv kind of work on plastics. Thermosettings are tough, brittle, and heat hardened.
When placed in a flame, thev will not burn readily, if at all. Thermosettings are so hard they resist the penetration of a knife blade, and any such attempt will dull the blade. If the plastic is immersed in hot water and allowed to remain, it will neither absorb moisture nor soften. Thermoplastics, on the other hand, when exposed to heat, become soft and pliable, or even melt.
When cooled, they retain the shape that they took under the application of heat. Some thermoplastics will even absorb a small amount of moisture, if placed in hot water. A knife blade will cut easily into thermoplastics. When testing a plastic by inserting it into a fire, you should exercise caution, because thermoplastics wi! If you use the fire test, be sure to hold the plastic piece a considerable distance away from you. Table 2B provides information on various groups of plastics. Laminated plastics are made by dipping, spraying, or brushing flat sheets or continuous rolls of paper, fabric, or wood veneer with resins, and then pressing several layers together to get hard, rigid, structural material.
As layers are added to paper-base material. Machining Operations Machining operations on plastics include cutting pxts from sheet ov rod stock, using various metal clotting saws; removing stock from parts by rotating tools such as in the drill press or the milling machine; cutting moving parts by stationary tools, as on the! Used for lenses, dials, etc. Cellulose nitrate Celluloid Ease of fabrication; relatively high impact strength and toughness; good dimensional stability and resilience; low moisture absorption.
Used for tool handles, mallet heads, clock dials, etc. Used for synthetic textiles, special types of bearings, etc. Absorption of water; large coefficient of expansion; relatively high cost; weathering resistance poor. Used for wire and cable insulation, and acid resistant clothing.
Used for preformed packing and gaskets. Not easily cemented; cannot be molded by usual methods; generates toxic fumes at high temperatures; high cost. Used for handles, telephone equipment, electrical insulators, etc. Used for instrument dials, electric parts, etc. Several types of saws budsaw, jigsaw, circular saw may be used to cut blanks from plastic stock. In drilling plastics, hack the drill rxlt frequently to remove the chips and cool the tool.
A liberal application of kerosene will help keep the drill cool. For plastics, set tlw tool slightI! For both thermosettings and thermoplastics. Plastic must Ix giveu a finishing process to remove tclol marks and pwclucc a clean, smooth surface.
Usually sanding and Mling iire sufficient for this purpose. Wet sanding can also be done by hnnd, with water and abrasive paper of fine grade. If n must be removed, it will large amount of material he more advantageous to nse sanding wheels or discs.
After pits and scratches have heen removed, the plastic should be huffed. This can be done on a wheel made of loose muslin huffs. A layer of the compound is deposited on the outside af the huffing whwl. The compound must Ix renewed frequently. Whdn large flat sheets we lacing huffed, be careful not to use too much pressure, nor to hold the work too long in one position. In bufliq small plnstic parts, Iw careful that the wheel does not seize the piece and pull it out of your grasp.
Chapter Generally a rule has four sets of graduations. The longest lines represent the inch marks. The other edge of this side is divided into sixteenths. The opposite side is similarly divided into 32 and 64 spaces per inch, and it is common practice to number every fourth division for easier reading.
There are many variations of the common rule. Sometimes the graduations are on one side only, sometimes a set of graduations is added across one end for measuring in narrow spaces, and sometimes only the first inch is divided into 64ths, with the remaining inches divided into 32nds and Eths.
These folding rules are usually 2 to 6 feet long. The foldirlg rules cannot be relied on for extrmeiy accurate measurements because a certain amount of play develops at the joints after they have been used for a while.
Steel tapes are made from 6 to about feet in length. The shorter lengths are frequently made with a curved cross section so that they are flexible enough to roll up but remain rigid when extended. Long, flat tapes require support over their full length when measuring, or the natural sag will cause an error in reading.
A hook is provided at one end to hook over the object being measured so a worker can handle it without assistance. HowCY Figure I. Types of rules. TII tat;! Cch coincides wit! To nlvasllw tlw insidr diameter of a pile with a ndr. Tnke the reading. In this case. By being free to move, the hook wil! To measure an inside dimension using a tape rule, extend the rule between the surfaces a.
The two inches are the width of the case. The total is the inside dimensior IE einx taken, Figure 8. Measuring an inside dimension with n tape rule.
Figure 6. Isxix DrxrExsmss. To takr an inside measurenirnt. Measuring thickness of stock through a hole. To measure the thickness of stock through a hole with a hook rule, insert the rule through the bole. To measure an outside dimension using a tape rule, hook the rule over the edge of the stock. For meawring widtlls. Measuring an outside dimension with a tape rule.
It may not always be possible to hook the end of rhc tape over the edge of stock being measured. Srcriw the book end of the tape. Hold the tape reel in the hand and allow it to unwind while walking in the direction in which the measurement is to be taken Stretch the tape with sufficient tension to overcome sagging. At the same time make sure the tape is parallel to an edge or the surface being measured.
Read the graduation on the tape by noting which line on the tape coincides with the measurcment being taken. Neoer allow the edges of measuring devices to become nicked by striking them with hard objects. They should preferably be kept in a wooden box when not in use. To avoid kinking tapes. With the spring-aid type tapes, guide the tape by hand. If it is allowed to snap back, it may be kinked, twisted, or otherwise damaged. Do not use the hook as a stop. Slow down as vou reach the end.
Calipers Simple calipers are used in conjunction with a scale to measure diameters. The calipers most commonly used are shown in Fig. TOOLS Otltsirle coiipers for measuring outside diameters arc bow-legged; those used for inside diameters have straight legs with the feet turnrd outward.
Spring-joint calipers have the legs joined by a strong spring hinge and linked together by a screw and adjustinl: nut. They are equipped with a small ausiliary leaf attached to one of the legs b!
The measurement is made as with ordinary calipers; then the leaf is locked to the leg. A different type of caliper is the hertnaphrodite sometimes called the odd-leg caliper. This caliper has one straight leg ending in a sharp point, sometimes removable, and one bow leg. The hermaphrodite caliper is used chiefly for locating the center of a shaft or for locating a shoulder. Using Calipers A caliper is usually rrsed in one of two ways. Either the caliper is set to the dimension of the work and the dimension transferred to a scale, or the caliper is set on a scale and the work machined until it checks with the dimension set up on the caliper.
To adjust a caliper to a scale dimension, one leg of the caliper should be held firmly against one end of the scale and the other leg adjusted to the desired dimension. To adjust a caliper to the work, open the legs wider than the work and then bring them down to the work. Caution: Neoer place a caliper work that is revolving in a machine. To measure the diameter of round stock, or the thickness of flat stock.
In rending the mensurement, sight over the leg of the caliper after making sure the caliper is set squarely with the face of the rule. Simpk noncalibrated FiFure To measure an almost inaccessible outside dimension, such as the thickness of the bottom of a cup, use an outside trmwfer firm-faint caliper, as shown in Fig.
Then loosen the bioding nnt and open the caliper enough to remove it from the cup. Close the caliper again and tighten the binding nut to seat in the slot at the end of the auxiliary arm. The caliper is now at the original setting, representing the thickness of the bottom of the cup. The caliper setting can now be measured with a rule.
To measure a hard-to-reach inside dimension, such as the internal groove shown in Fig. The procedure folInwed for measuring a hard-to-reach outside dimension is used.
Two SUBF. To measure the distance between two surfaces with an inside caliper, first set the caliper to the approximate distance being measured Fig. Hold the caliper with one leg in contact with one of the surfaces being measured. Then, as you increase the setting of the caliper, move the other leg from left to right.
To measure the dinmeter of R hole with an inside caliper, hold the caliper with one leg in contact with one side of the hole Fig. When you have found the point of largest diameter, remove the caliper and measure the caliper setting with a role. To set a combination firm-joint caliper with n rule, when the legs are in position for outside measurements, grasp the caliper with both hands, as shown in A, Fig.
By adjusting both legs, the shape of the tool will be approximately symmetrical. Thus, it will maintain its balance and be easier to handle. Setting- a combination firm-joint caliper Check this approximate setting ns shown in 13, Fig.
Sight squarely across the leg nt the graduations on the rule to get the exact setting required. If it is necessary to decrease or increase the setting, tap one leg of the caliper, as shown in Fig. The arrow indicates the change in setting that will take place. When the caliper is set for inside measurements, the same directions for adjusting thr setting apply.
To set a particular reading on an outside spring caliper, first open the caliper to the approximate setting. Then, as shown in Fig. Make the final setting by sighting over the other leg of the caliper, squars!
Setting inside spring caliper. Transferring measurement inside caliper. Setting combination firm-joint measulerrlentr. Setting outside spring caliper. The rule must be held sqwre! Adjust the knurled adjusting nut, reading the setting on the rule with line of sight normal to the face of the rule at the reading.
TG transfer a measurement from one spring caliper to another, hold the calipers as shown in Fig. When a slight dr ag is noticed, the caliper is at the proper setting.
Keep calipers clean and lightly oiled, but do not overoil the joint of firm-joint calipers or you may have difficulty in keeping them tight. Do not throw them around or use them for screwdrivers or pry bars. Even a slight force may spring the legs of a caliper so that other measurements made with it are never accurate. El-member, calir;ers are measuring instruments and must be used only for the purpose for which they are intended.
Slide Calipers The main disadvantage of using ordinary calipers is that they do not give a direct reading of a caliper setting. As explained previously, you must measure a caliper setting with a m! To overcome this disadvantage, use slide calipers Fig. Slide calipers can be used for measuring outside, inside, and other dimensions. One side of the caliper is used as a measuring rule, while the scale on the opposite side is used in measuring outside and inside dimensions.
Graduations on both scales are in inches and fractions thereof. A locking screw is incorporated to hold the slide caliper jaws in position during use.
Ilickness ot iiat stock, move the jaws of the caliper into firm contact with the surface of the stock. Read the measurement at thp reference line stamped OUT Fig. Measurina inside dimension xvith a slide caliper. TOOLS Note that two reference lines are needed if the caliper is to measure both outside and inside dimensions, and that thev are separated by an amount equal to the outside dimension of the rounded tips when the caliper is closed. Pocket slide calipers are valuable when extreme precision is not required.
They are frequentlv used for duplicating work when the expense of hxed gages is not warranted. Vernier Caliper A oernier caliper Fig. A sliding member is free to move on the bar and carries a jaw which matches the arm of an L. The vernier scale is engraved on a small plate that is attached to the sliding member.
The most distinct advantage of the vernier caliper, over other types of calipers, is its ability to provide very nccurate measurements over a large range. It can be used for both internal and external surfaces. Pocket models usually measwe from zero to 3 inches.
In using the vernier caliper, you must be able to read a vernier scale. The enlarged illustration shows two graduated scales; the top scale has divisions which are 0.
Therefore, the small 0. Rut when the zero graduation does not align with n graduation on the main scale, it can be readily determined how many thousandths the zero missed the 0. When the zero or index line the sliding scale does not quite reach the graduation, the amoust of misalignment must be subtracted, but when it passes the 0. Vernier caliper. Unfortunately, the O. Oi inch qndlutions are not too! Instead of 25 graduations crowded within the space of one n:ain scale division, the vernier graduations are arranged at intervals exactly 0.
This arrangement results in an accumulation of misalignments, starting with the first vernier graduation past the zero so that each may be marked as shown with a number representing the space in thousandths to the next upper scale graduation. For example, if the zero index line would be moved past the 8 inch graduation until the vernier graduation number 5 aligned with the next mair.
Figure 29 shows a bar 1 inch long divided by graduations into 40 parts so that each graduation indicates one-fortieth of an inch 0. Every fourth graduation is numbered; each number indicates tenths of an inch 4 x 0.
The vernier, which slides along the bar, is graduated into 25 divisions which together are as long as 24 divisions on the bar. Each division of the vernier is 0.
Verniers that are calibrated as just explained are known as English-measure verniers. The metric-measure vernier is read the same, except that the units of measurement are in millimeters. Vernier scale principle. Expanded view, of vernier scale. En,dish rwacure vernier scale A, Fig. Because the zero mark on the vernier is a little past a 0. In this case it is at the 0. The reading on the caliper shown in C, Fig. Follow the above procedure. You should read 2.
To read a metric-measure vernier, note the nombel of millimeters and the 0. Then add the nomber of how dredths of a millimeter indicated by the line on the vernirr that coincides with a line on the scale. For example, A, Fig. The reading in B, Fig. If R vernier caliper is calibrated in either English measure or in metric measure, usually one side will be calibrated to take outside measurements and the other to take inside mcasrnements directly. The vernier plate for inside measurements is set to compensate for the thickness of the measuring points of the tools.
But if n vernier caliper is calibrated for both English and metric measure, one of the scales will appear on one side and one on the other. Then it will be necessary. For example, Table 3 shows the amounts to be added for various sizes of vernier calipers.
To measure the distance between outside surfaces or the outside diameter of round stock with a vernier caliper, steady the stock with one hand and hold the caliper in the other, as shown in Fig. In the illustration, the clamping screws are at A and B; the horizontal adjusting screw nut is at C.
With A and B loose, slide the movable jaw toward the piece being measured until it is ahnost in contact. Then tighten A to make C operative. With C, adjust the movable jaw to the proper feel and secure the setting with B. The reading can then be taken as previously explained. To measure the distance between inside surfaces, or the inside diameter of a hole, with s vernier onliper, use the scale marked inside. Figure 33 shows the measuring points in place.
Fignan Mcawring ir. Set Figs. The orc! Ietcr is! YOri use the SG! Micrometer-rending exercises. To read this to three decimal places. To read it to four decimal places estimate the number of tenths of the distance betwrer. Each tenth of this distance equals one ten-thousandth O. OOOl of an inch. Add the ten-thousandths to the reading as shown in the calculations of B, Fig.
Figure cdipm I? The correct readings are given ioI? Enterpulating a micrometer reading. Wendin:: a wrnirr micrometer diprr Fig. This is because tbis microme! Therefol-e, as you turn the thimble clockwise on this micrometer. Hold one end in place witb one hand 21syou feel for the maximum possible setting I! Wherl no left-to-right movement is possible, and a slight drag is noticed on the in-and-out-swing, take the reading.
Hold the micrometer in the other hand so that the thimble rests between the thumb and the forefinger see Fig. Measuring round stock with a micrometer caliper. Turn the spindle down to contact by feel, or else tie the ratchet stop. Your feel should produce the same colttact pressure and therefore the same reading as that produced when the ratchet stop is used. Develop your feel by measuring a certain dimension both with and without the aid of the ratchet stop.
When you have the correct feel, you will get the same readings bv hoth methods. This tends to give a reading smaller than the trw readingI unless the light feel is wed. Moreover, in meaxring n hall from n hall bearing. When measuring a flat surfacewith a micrometer caliper, the entire area of both the anvil and the spindle is in contact with the surface being measured. On large fZat work, it is necessary to!
The frame is held 1 cme hand to position it and to locate it sqwue to the measured surface. The other hand operates the thimble either directly or through the ratchet. A large, flat surface should be measured in several places to determine the amount of variation. It is good practice to lock the spindle in place with the locknut before removing the micrometer from the part being measured.
After removal of the micrometer the measurement indicated on the thimble scale can then be read. To retain a particular setting, in cases where several pieces are to be gaged, lock the spindle in place with the locknut. Blades are no-mall - six or right inches long. The sliding T-bevel is nsed for laying out angles other than I-ight angles. To adjust a sliding T-bevel to a drsired settins, loosen the blade screw. To set the blade nt a 45degree angle, hold the handle against R framing sqrtare as shown in A, Fig.
When using drafting IA:-TI- bevel, different size triangles for setting :a. A sliding T-bevel can be set to anv desired angle by using a protractor. Face ik sourw of light. This is a V-shaped member so designed that the center uf the This attachment is useful when locating the exact center of round stock.
The protractor head, commonly called R bevel protractor, can be attached to the scale, adjusted to any position on it, and turned and locked at any desired angle. Angular graduations usually read from 0 to degrees both ways, permitting the supplement of the angle to be read.
A spirit level may be included on some models, forming, in effect. The appearance of iight betwem the blade and the surface of the stock indicates where the angle is not correct Figure 48 indicates the checking of a bevel.
Core of Squares Make certain that the blades, heads, dials, and all accessories are clean. Apply a light coat of oil on all metal surfaces to prevent rusting when not in use. Do noi xse sqwires for pcrposes other than those intended. When storing squares or bevels for long periods of time, apply a liberal amount of oil or rustpreventive compound to all surfaces, wrap in oiled paper or cloth, and place in containers or on racks away from other tools.
Testing tmerress of a bevel, Combination Square. These combine the functions of several tools, and serve a wide variety of purposes. See Figs. Normally only one head is used at a time. The square lxxx1 may be adjusted to any position along the scale and clamped securely in place. The combination square can thus serve as a depth gage, height gage, or scribing gage. Combination square Set. These gages have R range from 0 to 9 inches, depending on the length of extension rod used.
Some are provided with a ratchet stop. Tbc flat base ranges in size from 2 to fi inches. Several extension rods are normally supplied with this typr of gage.
To measure the depth of a hole or slot with rensonnble accurac , use a depth gage as shown in A, Fig. Using depth gages. Tighten the setscxv to maintain the setting. Safe that the clamping screws ;w ;tt S and Y; and the horizontal adjusting screw lllit is at Z.
Kit11 X and Y loose, slide the scale down htu the slot being measured until it is almost in contact. With Z, adjust the scale to the proper feel and secure the setting with Y.
By proper feel is meant the adjEstnm:t at which you first notice contact between the end of the scale and the bottom of the slot. Then read the setting as previously described under Reading a Vernier Scale. To set the vernier depth gage to n particnIar setting, loosen both setscrews at S and at Y and slide the scale through the gqe to tbr approximate setting. Tighten the setscrew nt S, turn the knurled nut at Z until the desired setting is made; and tighten the setscrew at Y to hold the setting.
To measure the depth of a hole or slot, as shown in C, Fig. Remove the micrometer from the work and read the micrometer. Remember, if extension rods are used, the total depth reading will he the sum of the length of the rods plus the rending on the micrometer. Surface gage. The surface gage Fig. Surface gages ax made in seve:al sizes and are classified by the length of the spindle, the smallest spindle being 4 inches long, the average 9 to 12 inches long and the largest 18 inches.
The bottom and the front end of the base of the surface gage have deep V-grooves cut in them, which allow the gage to be seated on n cylindrical surface. The spindle of a surface gage may be adjusted to any position with respect to the base and tightened in place with the spindle nut.
The rocket adjusting screw provides for the finer adjustment of the spindle by pivoting the spindle rocket bracket. The scriber can be positioned at any height and in any desired direction on the spindle by tightening the scriber nut.
The scriber may also be mounted directly in the spindle nut mounting, in place of the spindle, and used where the working space is limited and the height of the work is within range of the scriber. Use either a combination square or it rule with rule holder to get the measurement.
A rule aiorre cannot be held securely without wobbling and consequentl! Because a combination square is generally available, its use for setting a surface gage is expEained in this section. Piace the squaring head of a combination square on a flat surface, as shown in Fig. Surface plate, Figure Setting a surface gage tc height. Surface For very fine work, lightly coat the surface plate with prussian blue bearing blue and move the piece being tested across the blue surface Fig.
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