[metalworking]weldingandmachining(1-1000).pdf

1、MachiningTable of Contents.htmWeldingTable of Contents.htm MACHININGFundamentals and ApplicationBack to CD-ROM Contents Table of ContentsCHAPTER 1.Introduction to the Machine ShopCHAPTER 2.Properties,Identification,and Heat Treatment of MetalsCHAPTER 3.Portable Machine ToolsCHAPTER 4.Drilling Machin

2、esCHAPTER 5.Grinding MachinesCHAPTER 6.Sawing MachinesCHAPTER 7.LathesCHAPTER 8.Milling OperationsCHAPTER 9.Milling-Grinding-Drilling and Slotting Attachment(Versa-Mil)APPENDIX A.TablesAPPENDIX B.Weights and MeasuresAPPENDIX C.FormulasGLOSSARYMACHINE SHOP WORK SCOPE Machine shop work is generally un

3、derstood to include all cold-metal work by which an operator,using either power driven equipment or hand tools,removes a portion of the metal and shapes it to some specified form or size.It does not include sheet metal work and coppersmithing.LAYING OUT WORK Laying out is a shop term which means to

4、scribe lines,circles,centers,and so forth,upon the surface of any material to serve as a guide in shaping the finished workpiece.This laying out procedure is similar to shop drawing but differs from it in one important respect.The lines on a shop drawing are used for reference purposes only and are

5、not measured or transferred.In layout work,even a slight error in scribing a line or center may result in a corresponding or greater error in the finished workpiece,For that reason,all scribed lines should be exactly located and all scriber,divider,and center points should be exact and sharp.SCRIBIN

6、G LINES ON METAL The shiny surface,found on most metals,makes it difficult to see the layout lines.Layout dye(Figure 1-2),when applied to the metal surface,makes it easier for the layout lines to be seen.Layout dye is usually blue and offers an excellent contrast between the metal and the layout lin

7、es.Before applying layout dye,ensure that all grease and oil has been cleaned from the work surface.Otherwise the dye will not adhere properly.COMMON LAYOUT TOOLS ScriberTo obtain an accurate layout,fine lines must be scribed in the metal.A scriber(Figure 1-3)is the layout tool that is used to produ

8、ce these lines.The point is made of hardened steel and is kept sharp by honing on an oilstone.DividerWhen laying out circles,arcs,and radii,it is best to use the divider(Figure 1-4).The legs of the divider must be of the same length and be kept sharp.The divider can be used to lay out and measure di

9、stances(Figure 1-5).To set the divider to the correct length,place one point on an inch mark of a steel rule and open the divider until the other leg matches the correct measurement required(Figure 1-6).TrammelWhen scribing circles,arcs,and radii that are too large to be produced with the divider,a

10、trammel should be used(Figure 1-7).The trammel is made of three main parts:the beam,two sliding heads with scriber points,and an adjusting screw that is attached to one of the heads.The trammel can be made to scribe larger distances with the use of extension rods.This layout tool is set in the same

11、manner as the divider.Hermaphrodite CaliperThe hermaphrodite caliper(Figure 1-8)is a tool used to lay out lines that are parallel with the edges of the workpiece(Figure 1-9).It can also be used to locate the center of cylindrical shaped workplaces(Figure 1-10).Surface Gage A surface gage(Figure 1-11

12、)is used for many purposes,but is most often used for layout work.The gage can be used to scribe layout lines at any given distance parallel to the work surface(Figure 1-12).The spindle may be adjusted to any position with respect to the base and tightened in place with the spindle nut(Figure 1-11).

13、The rocker adjusting screw provides for finer adjustment of the spindle by pivoting the spindle rocker bracket.The scriber can be positioned at any height and in any desired direction on the spindle by adjusting the scriber.A surface plate and combination square(Figure 1-13)are needed to set the sur

14、face gage to the correct dimension.Surface Plate A surface plate(Figure 1-14)provides a true,smooth,plane surface.It is used in conjunction with surface and height gages as a level base on which the gages and the workpiece are placed to obtain accurate measurements.These plates are made of semi-stee

15、l or granite and should never be used for any job that would scratch or nick the surface.Vernier Height Gage The vernier height gage(Figure 1-15)is a caliper with a special foot block to adapt it for use on a surface plate.Height gages are available in several sizes:the most common are the 10,18,and

16、 24 inch gages in English measure and the 25 and 46 cm gages in metric measure.Like the vernier caliper,these height gages are graduated in divisions of 0.025 inch and a vernier scale of 25 units for reading measurements to thousandths of an inch.Always be sure the bottom of the foot block(Figure 1-

17、15)is clean and free from burrs.Figure 1-16 shows the height gage with a tungsten carbide marker.This marker is used to lay out lines on glass,hardened steel,or other hard materials.Figure 1-17 illustrates the use of an offset scriber with the height gage.This scriber reaches below the gage base.Do

18、not attempt to adjust the sliding jaw while it is clamped to the upright beam.Combination Square Set The combination square set(Figure 1-18)is used for a number of layout operations.The set consists of a blade(graduated rule),square head,protractor,and center head.Blade The blade is designed to allo

19、w the different heads to slide along the blade and be clamped at any desired location.The groove in the blade is concave to eliminate dirt buildup and permit a free and easy slide for the heads.By removing all the heads,the blade may be used alone as a rule.Square Head The square head is designed wi

20、th a 45 and 90 edge,which makes it possible to be used as a try square and miter square.By extending the blade below the square,it can be used as a depth rule.The square head can also be used as a level.Protractor Head The protractor head is equipped with a revolving turret graduated in degrees from

21、 0 to 180 or to 90 in either direction.It is used to measure or lay out angles to an accuracy of 1.Center Head The center head,when inserted on the blade,is used to locate and lay out the center of cylindrical workpieces.Bevel Protractor The bevel protractor(Figure 1-19)consists of an adjustable bla

22、de with a graduated dial.The blade is usually 12 inches long and 1/16 inch thick.The dial is graduated in degrees through a complete circle of 360.The most common use for this tool is laying out precision angles.The vernier scale is used for accurate angle adjustments and is accurate to 5 minutes or

23、 1/12.STEPS IN MAKING A LAYOUT Planning before beginning any layout is one of the most important steps.Each job may require different layout tools depending on the accuracy needed;however,there are certain procedures which should be followed in any layout.Figure 1-20 shows a typical layout.G G Study

24、 the shop drawing or blueprint carefully before you cut off the stock.Allow enough material to square the ends if required.G G Remove all oil and grease from the work surface and apply layout dye.G G Locate and scribe a reference or base line.All the other measurements should be made from this.If th

25、e workpiece already has one true edge,it can be used in place of the reference line.G G Using the base line as a reference line,locate and scribe all center lines for each circle,radius,or arc.G G Mark the points where the center lines intersect using a sharp prick punch.G G Scribe all circles,radii

26、,and arcs using the divider or trammel.G G Using the correct type protractor,locate and scribe all straight and angular lines.G G Scribe all lines for internal openings.G G All layout lines should be clean,sharp,and fine.Reapply layout dye to all messy,wide,or incorrect lines and rescribe.The layout

27、 tools mentioned in this section are only the most commonly used.JIGS AND FIXTURES The primary purpose of jigs and fixtures is to align the tool and hold the workpiece properly during machining.A fixture is a device which holds the work while cutting tools are in operation.It differs from a jig in t

28、hat it has no guides or special arrangements for guiding tools.A jig is also a fixture for locating or holding the work and guiding the cutting tool in operations such as drilling,reaming,counterboring,and countersinking.Jigs and fixtures can greatly reduce the cost of manufacturing large quantities

29、 of parts.Their use is also an advantage when the interchangeability and accuracy of the finished products are important.They also can be used in low or limited production jobs if extreme accuracy must be maintained.One of their greatest advantages is that relatively unskilled labor can accomplish t

30、he job using these special tools.MECHANICAL DRAWINGS AND BLUEPRINTS Mechanical Drawings A mechanical drawing,made with special instruments and tools,gives a true representation of an object to be made,including its shape,size,description,material to be used,and method of manufacture.Blueprints A blu

31、eprint is an exact duplicate of a mechanical drawing.These are the most economical and satisfactory working drawings in use.They do not soil easily and are comparatively easy to read.Blueprint paper is a good grade of white paper coated with a chemical solution,making it greenish yellow.A blueprint

32、is made by placing a tracing of a mechanical drawing on a sheet of blueprint paper and exposing it to light.During exposure,the light penetrates where there are no lines or printing on the tracing but does not penetrate where there are lines or printing.The print is then washed in water,which change

33、s the exposed chemical to a dark blue and washes the chemical off where lines and printing prevented exposure.In other words,the process leaves white lines on dark blue background.Working From Drawings Detail prints usually show only the individual part or piece that must be produced.They show two o

34、r more orthographic(straight-on)views of the object,and in special cases,they may show an isometric projection,without dimension lines,near the upper right corner.An isometric projection shows how the part will look when made.Each drawing or blueprint carries a number,located in the upper left-hand

35、corner and in the title box in the lower right-hand corner of the print.The title box also shows the part name,the scale used,the pattern number,the material required,the assembly or subassembly print number to which the part belongs,the job order number,the quantity and date of the order,and the na

36、mes or initials of the persons who drew,checked,and approved the drawings(Figure 1-20).Accurate and satisfactory fabrication of a part described on a drawing depends upon the following:G G Correctly reading the drawing and closely observing all data on the drawing.G G Selecting the correct tools and

37、 instruments for laying out the job.G G Use the baseline or reference line method of locating the dimensional points during layout,thereby avoiding cumulative errors.G G Strictly observing tolerances and allowances.G G Accurate gaging and measuring of work throughout the fabricating process.G G Givi

38、ng due consideration when measuring for expansion of the workpiece by heat generated by the cutting operations.This is especially important when checking dimensions during operations,if work is being machined to close tolerances.Limits of Accuracy Work must be performed within the limits of accuracy

39、 specified on the drawing.A clear understanding of tolerance and allowance will help you avoid making small,but potentially large errors.These terms may seem closely related but each has a very precise meaning and application.The paragraphs below point out the meanings of these terms and the importa

40、nce of observing the distinctions between them.Tolerance Working to the absolute or exact basic dimension is impractical and unnecessary in most instances;therefore,the designer calculates,in addition to the basic dimensions,an allowable variation.The amount of variation,or limit of error permissibl

41、e is indicated on the drawing as plus or minus(+)a given amount,such as+0.005 or+1/64.The difference between the allowable minimum and the allowable maximum dimension is tolerance.When tolerances are not actually specified on a drawing,fairly concrete assumptions can be made concerning the accuracy

42、expected,by using the following principles.For dimensions which end in a fraction of an inch,such as 1/8,1/16,1/32,1/64,consider the expected accuracy to be to the nearest 1/64 inch.When the dimension is given in decimal form the following applies:If a dimension is given as 2.000 inches,the accuracy

43、 expected is+0.005 inch;or if the dimension is given as 2.00 inches,the accuracy expected is+0.010 inch.The+0.005 is called in shop terms,plus or minus five thousandths of an inch.The+0.010 is called plus or minus ten thousandths of an inch.AllowanceAllowance is an intentional difference in dimensio

44、ns of mating parts to provide the desired fit.A clearance allowance permits movement between mating parts when assembled.For example,when a hole with a 0.250-inch diameter is fitted with a shaft that has a 0.245-inch diameter,the clearance allowance is 0.005 inch.An interference allowance is the opp

45、osite of a clearance allowance.The difference in dimensions in this case provides a tight fit.Force is required when assembling parts which have an interference allowance.If a shaft with a 0.251-inch diameter is fitted in the hole identified in the preceding example,the difference between the dimens

46、ions will give an interference allowance of 0.001 inch.As the shaft is larger than the hole,force is necessary to assemble the parts.Precautions Be sure you have the correct print for the part to be made or repaired.You want the print which has not only the correct title,but also the correct assembl

47、y number.Never take a measurement with a rule directly from the print because the tracing from which the print was made may not have been copied from the original drawing perfectly and may contain scaling errors.Also,paper stretches and shrinks with changes in atmospheric conditions.Dimensions must

48、be taken only from the figures shown on the dimension lines.Be very careful in handling all blueprints and working drawings.When they are not in use,place them on a shelf,in a cabinet,or in a drawer.Return them to the blueprint file as soon as the job is done.Blueprints and working drawings are alwa

49、ys valuable and often irreplaceable.Make it a point never to mutilate,destroy,or lose a blueprint.GENERAL SHOP SAFETY All tools are dangerous if used improperly or carelessly.Working safely is the first thing the user or operator should learn because the safe way is the correct way.A person learning

50、 to operate machine tools must first learn the safety regulations and precautions for each tool or machine.Most accidents are caused by not following prescribed procedures.Develop safe work habits rather than suffer the consequences of an accident.Most of the safety practices mentioned in this secti