How to reduce costly errors when reverse engineering mechanical parts

1. How to Minimize Error When Reverse Engineering Precision Parts
Reverse engineeringprecisionmechanical partsisnota perfectscience andischock-full of opportunities
for errorboth large and small.Toeveryone responsiblethe errorsequate to$ sometimessmalland
sometimesvery $$$large.Likewise,the actual errorscanbe slightdimensional differences, ormajor
featuresmissingorfeatures inthe wrongposition entirely.Like all goodprocesses,ithelpstohave a
documentedprocedure tofollowalongwithachecklistthatis savedforeach part.Even if youare a
seasonedproat this,itiseasyto get distractedandforgetsomething whichgetshardertocorrectthe
furtheryouget downthe line,especiallyif the parthasalreadybeenmachined! Ilike tohave areminder
that I didn’tskipanyessential processstepthatcouldcause issueslater.
internal process checklist
Reverse Engineering Process Checklist

2. Clean, degrease, remove metal fragment and other foreign substances.
From myperspective we are alwaysthinkingthatwe are goingto be scanningthe parts so a perfectly
cleanpart isessential, butwhenusinganytype of “hardmeasurement”tools youare goingto
compromise accuracyby measuringdirtysurfacesoftenmeasuringthe dirtandnotthe surface,notto
mentiongettingthe grease andgunkonyourmeasuringtools,whichwill cause youproblemsinfuture
project,unlesscleanedupafter.

4. Pictures
I like totake picturesof the part from everyangle andcapture everysurface asthe sayinggoes“a
picture iswortha thousandwords.”Thisprovidesarecordof the original partwhichcan be valuable
duringmodelingandequallyvaluable if anyquestionsarise downthe line afteryouare complete.

5. Checking overall part length via height
Hard Measurements
Although3D scanningwithqualityequipmentandexperiencedandknowledgeable personnel canbe
bothaccurate and precise itisalwaysa goodpractice to capture any harddata that is easilyavailable.I
especiallytrytocapture overall dimensionsincase stockhastobe orderedforthe replacementpartsas
well ashole diameters. Thisisespeciallyimportantforsmall holes.Iusuallyuse aplugandpingages and
evenleave theminduringscanning,sinceitiseasiertopickout a cylinderratherthana hole while you
are modelingthe part. Youalsoneedtocapture featuressuchasthreadedholessize andpitchaswell as
depthsandcounterbore/countersinksdimension. Again,thisprovidesagoodreference whileyouare
modelingthe partas well as,aquickconfirmationthatsome sortof inadvertentscalinghappened
betweenconversionsaswell as,aquickcheck if issues regardingaccuracycome up afteryouare done.

6. Laser scanned mesh model of part
Scan data
Of course, nothingcanbeataccurate scan data. Whenyoubringthisintoyour reverse engineering
applicationyouhave atremendousamountof 3D data inyour workspace todevelopacomplete CAD
model of yourpart.

7. CAD model of part created from scan

8. Checking surface curvature continuity
Modeling
While modeling,reference hardreference dataespeciallywithfeaturesthatare hard to resolve from
the scan data. Checksurface curvature continuity. Alsokeepinmindthe designintent.Isthe partto be
simplyareproductionof whatisavailable orare there improvementsandorchangesto be made.
Sometimesthe partmayhave a set of surfacesmissingthatwere damagedinmanufacturing.These
oftenhave tobe carefullyreproducedbasedonthe “bestavailable”information.Finally,make Ilike to
make sure that the part is alignedinthe X,Y,Z coordinate systeminaway thatmakessense forthe
customerand the application.

9. Scan to CAD comparison
Compare CAD to original scan
As a final check,we runa CADto part analysistosee if anythingismissingora surface isout of the
anticipatedtolerance zone.
William DPlutnick
WilliamD.Plutnick
President/CEO | Swiss Metrology

10. 16 South Queen St. Mt. Sterling, KY 40353
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