1、10FTM09AGMA Technical PaperReverse EngineeringBy Charles D. Schultz, BeytaGear ServiceReverse EngineeringCharles D. Schultz, Beyta Gear ServiceThe statements and opinions contained herein are those of the author and should not be construed as anofficial action or opinion of the American Gear Manufac
2、turers Association.AbstractAs Americas manufacturing base has contracted the need for reverse engineering has grown. Wellestablished suppliers have disappeared, often leaving customers with no source of spare parts or technicalsupport. Over time certain pieces of equipment require changes to output
3、speeds or power levels and newparts have to be designed, built, and installed. And unfortunately, some pieces of equipment dont measure upto the demands they are subjected to and need redesign or improvement. In many ways, reverse engineeringis just as demanding a discipline as original product deve
4、lopment with many of the same challenges but plusthe additional restrictions of fitting inside of an existing envelope.The typical reverse engineering project begins with very limited information on the existing piece ofequipment. This paper will describe a methodology for the reliable measurement,
5、evaluation, re-design, andmanufacture of replacement parts for gearboxes and industrial machinery. A step-by-step example will beprovided.Copyright 2010American Gear Manufacturers Association500 Montgomery Street, Suite 350Alexandria, Virginia, 22314October 2010ISBN: 978-1-55589-984-43Reverse Engine
6、eringCharles D. Schultz, Beyta Gear ServiceReverse engineering is a necessary activity in themodern industrial world. Rather than mount adefense against those who label it “copying”, theauthor would prefer to point out the long andhonored history of the practice of studying a com-petitors product an
7、d using the knowledge gained toimprove your own products. The largest, most wellfunded industrial organizations in the world spendmillions of dollars each year on “competitiveanalysis”, despite what their intellectual property at-torneys might want you to think. The entireautomotive aftermarket sect
8、or exists because ofreverse engineering. Where would car restorers bewithout reverse engineering?As Americas manufacturing base has contracted,the need for reverse engineering has grown. Wellestablished suppliers have disappeared, oftenleaving customers with no source of spare parts ortechnical supp
9、ort. Over time, certain pieces ofequipment require changes to output speeds orpower levels and new parts have to be designed,built, and installed. Unfortunately, some pieces ofequipment dont measure up to the demands theyare subjected to and need redesign or improve-ment. In many ways, reverse engin
10、eering is just asdemanding a discipline as original product develop-ment with many of the same challenges, plus theadditional restrictions of fitting inside of an existingenvelope.As engineers, we have an obligation to behave in anethical manner and to respect the intellectualproperty rights of othe
11、rs. It is recommended thatany questions on possible infringement or conflictbe discussed with your legal advisors before pro-ceeding.Reverse engineering processThe typical reverse engineering project begins withvery limited information on the existing piece ofequipment. Whether the need is a critica
12、l compon-ent for your own “down machine”, or a customerwith a broken gizmo in the back of his truck, peopleexpect an engineer to develop a solution in a veryshort time. See Figure 1.What is the part from?If you know what the part is from, you can simplifyyour decision making later. Knowing what it i
13、s fromhelps you determine if replacement parts might beavailable from someone, somewhere. If parts areavailable you can often scrub the entire reverse en-gineering activity or get by with a temporary sparewhile the “good parts” are in transit. If parts arentavailable you can concentrate your efforts
14、 onmaking the best parts possible with a clearconscience.Another benefit of knowing where the parts arefrom, is the insight it provides on the machine de-signers original intent and limitations. For example,a European or Asian machine will most certainly be“metric.” An older American machine will al
15、mostcertainly be “customary units”. As youll see fromour example, machines from the United Kingdommay be either system. The vintage of the machinewill also tell you much about the materials andtechnology involved in its design; this is a big help indeciding the level of reverse engineering needed.Wh
16、y did it break?There is little sense in making spare parts in a hurryif you are just going to break something else in themachine as soon as it starts up. Think “shear pins” -one can easily make stronger shear pins for an out-board motor propeller. The problem is you get stuckfar from shore with an i
17、mpossible to repair lower unitfailure.If the part “just wore out” you may want to ask whybefore making spares. Was preventive mainten-ance or lubrication lacking? Are related parts also inneed of adjustment or replacement? Once amachine is down you might as well fix it right; thenext failure might n
18、ot be so easy to access.4Figure 1. Reverse engineering flow chart5What does it do?The function of a part may affect how you make thereplacement or if you even want to try. Useextreme caution in reverse engineering parts thatcould injure people if they break or malfunction.Unless you know the functio
19、n of a part, you cantproperly understand the loads imposed on it. If youdont know the loads you cant intelligently selectmaterials, processes, or tolerances for thereplacement part.How was it made?Complex castings are not easy to replace or repair.There is a temptation to ignore this step of thereve
20、rse engineering process and simply make fab-ricated or billet replacements. Careful examinationof the “how” of the old part can provide valuableinformation. More than one “casting” has turned outto be an assembly upon close examination.Complex timing relationships between part featurescan also be mi
21、ssed if the original manufacturingmethod is not determined.What is it made of?“Cast iron”, “aluminum”, “bronze”, and “steel” arenot sufficient descriptions from which to makereplacement parts. Informed decisions requiremore than these generic material classifications. Itis particularly important to
22、understand the originaldesigners reasoning in selecting the material if achange in material type is planned. Was aluminumused because it was inexpensive at the time, or be-cause the rotating inertia had to be minimized? Wascast iron specified for cost savings, or to achieve abeneficial difference in
23、 material in a rotary joint?Was the part surface hardened, through hardened,or not hardened at all? (If you do not have access tohardness testing equipment, check an edge of thepart with a file. Soft materials will file easily, throughhardened less easily, and surface hardened oneswith great difficu
24、lty or not at all. In a pinchsandpaper will substitute for a file.) Was a sacrificialcoating applied, and if so, for what reason? Failureto investigate the material selection may result in avery expensive problem in the future.Do we have a part drawing or a sketch in theservice manual?The more broke
25、n the part, the more difficult it is toreverse engineer from the artifact. A machinebuilder may be willing to share a drawing if they areunable to furnish a part. It seldom hurts to ask. Inthe absence of a detailed part drawing, it is veryhelpful to have an exploded parts drawing orassembly cross se
26、ction view. If you know whatbearings, seals, snap rings, fasteners, or matingparts interface with the failed item it is much easierto make a new drawing. Each interface you “know”provides a wealth of information about the sizes,tolerances, fit, and finish needed.Make the drawingCleanliness is critic
27、alIf you have to make a new detail drawing, start bygetting the part as clean as you can. Dirty partsmake for grimy sketches, inaccuratemeasurements, missed features, and undiscovereddefects.Safety firstDont rush yourself into a first aid situation. Takeextra precautions if the part has sharp edges,
28、weighs more than a few pounds, or cannot be setinto a secure, stable position. Make certain thework area is well lit, free of slip or trip hazards, andaway from lift truck traffic before attempting tomeasure it.Photograph everythingThere is no substitute for clear digital photos of thepart from ever
29、y angle. What you think you saw maynot be so a few days later when everyone has had agood nights sleep and the part is no longer in thesame condition. Photos make an excellent substi-tute for hand drawn sketches if you neatly mark themeasurements directly on the printouts.Measure everything several
30、times and write itdownPoor penmanship, typographical errors, andtransportation have derailed many rush repair pro-jects. The best defense is writing things downpromptly and having several people make their ownmeasurements. Thoroughly cleaning the part (asadvocated earlier) really helps here.For part
31、s with gears or splines, count the teethcarefully (several times), and write the results on thepart with a marker or paint stick. Measure theoutside diameter carefully; if the number of teeth isodd or the part is missing some teeth, even a partial6measurement is better than none. Wheneverpossible tr
32、y to measure the center distance and geta count of the mating teeth. Take a span measure-ment over different numbers of teeth or measure thesize over pins or wires. It is great if you have the“right” measuring pins or the “correct” number ofteeth to span but any data is better than none.Measurements
33、 over different size wires or pins canhelp determine the pressure angle needed. Toothgages are handy tools to have if you anticipatedoing a lot of reverse engineering.Bevel and worm gears should be replaced as sets.If you replace just one member dont expect a longservice life.Most gears and splines
34、are made with standardtools to standard or slightly modified dimensions. Ifyour measurements say otherwise, you would bewell served to have someone else confirm thedimensions. Even “custom” gear sets can bereplaced with more standard geometry if you care-fully think things through.Always remember th
35、at you are measuring a worn orfailed part. Particularly when standard componentslike bearings, seals, snap rings, keys, and locknutsare used, it is more likely that “standard” dimensionswill apply.Make a proper drawing or sketch; then checkthe artifact to itIf there is one crucial step most commonly
36、 skipped,it is this one. Here is one final chance to catch that0.025” error in reading a micrometer or that 1” erroron the overall length. If at all possible havesomeone not involved in the original measuring andsketching check the parts. If discrepancies are dis-covered at this stage, cheerfully re
37、peat the stepsabove and be thankful you didnt waste time andmaterial making a piece of scrap.Carefully consider “upgrades”Just because you can “upgrade” the replacementpart doesnt mean you should. Keep that shear pinanalogy in mind. If it lasted 50 years without heattreatment it probably will again.
38、 If, however, it failedbecause of lack of strength or surface hardness goahead and make it “better”,Making the spare partStay involved with the project while the spare part isbeing made. Double check any purchasedcomponents. Be available to answer questions or tosupervise assembly and installation.D
39、ocument the “as built” condition beforeclosing the book on the projectDouble check the finished part against your finaldrawing to make sure the drawing reflects what wasactually made. When spares are made in a hurryother people may have decided to skip steps, altersizes, or modify features without i
40、nforming you.Your drawing may have been wrong or a tolerancemay have been too tight to hold. If you dont checkthe part you wont know what caused the second“failure” or you may make another set of spares at alater date that wont fit or work as well.Example problemVintage motor racing has become very
41、populararound the world. An unfortunate consequence ofactually operating the cars is the failure of compon-ents for which spares are not available. Inability torace the vehicle greatly affects the market value. Inthe case of our example car, a 1991 BennettonFormula 1 car, a static display car, see F
42、igure 2, isworth $250,000 while a running car could bring over$1,000,000, see Figure 3. High level race cars arevery expensive to operate and are very mainten-ance intensive. In actual competition, over 100 manhours are spent in the shop for every hour on thetrack. Top level F1 teams spend $100,000,
43、000 percar per season and have hundreds of highly skilledemployees.Figure 2. Static display Bennetton Formula 1car7Figure 3. Vintage racing Bennetton Formula 1carRapidly changing technology, operational secrecy,and highly stressed parts makes it very difficult toobtain spares once the race cars are
44、retired fromcompetition. This is particularly true in Formula 1where even the very top teams may only have ahandful of cars. Contrast this to NASCAR where atypical team has several dozen cars at the shop foreach one brought to the track. Until recently For-mula 1 rules discouraged sharing components
45、between teams so many unique parts are involved.Drawings are very difficult to obtain.The owner of our example car was fortunate toobtain many spare parts but was down to his last setof trans axle oil pump gears, see Figure 4. Thetrans axle case is cast magnesium and anyassembly or disassembly requi
46、res heating the en-tire case to 300 F degrees in an oven. While itwould be possible to retrofit the car with a separateelectric oil pump, such a change would detract fromthe authenticity and resale value, see Figure 5. Theleast damaged set of gears was provided for meas-urement along with the parts
47、upon which theymounted. Following the procedure outlined above,preliminary part drawings were made by the author.Figure 4. Oil pump drive componentsFigure 5. Assembled trans axleThe parts and the drawings were then delivered tothe gear supplier for further review. The shopchosen for this project has
48、 been reverse engineer-ing rare parts for many years, including a completetransmission set for a Duesenberg and a spiralbevel set for a 1980 Ferrari Formula 1 car. The shopchecked the parts against the reverse engineereddrawing and found several errors. After revision, anorder was placed for (5) set
49、s of oil pump gears. Theparts are small and making a larger quantity spreadthe set-up costs while allowing the car owner torecoup some of his expenses by selling two sets toanother Bennetton enthusiast. See Figure 6 andFigure 7.Fortunately, these parts used standard inch serieshobs and splines. This saved the time and expenseof obtaining custom gear cutting tools. Had specialtools been required, the owner would have faced apainful decision on just how authentic he couldafford to be. These parts are very deep in the transaxle and would never be seen by anyone othe
