Presentation on theme: "Finishing Processes - Reaming, Broaching, and Lapping"— Presentation transcript:
1Finishing Processes - Reaming, Broaching, and Lapping Unit 25
2ObjectivesIdentify and explain the purpose of several types of hand reamersReam a hole accurately with a hand reamerCut a keyway in a workpiece using a broach and arbor pressLap a hole or an external diameter of a workpiece to size and finish
3Hand Cutting Tools Reamers Broaches Lapping Used to bring hole to size and produce good finishBroachesUsed with arbor press to produce special shapes in workpieceMulti-tooth tool forced through holeLappingWhere very fine abrasive powder, embedded in tool is used to remove minute amounts of material from surface
9Reaming PrecautionsNever turn reamer backward (counterclockwise), it will dull teethUse cutting lubricant where requiredAlways use helical-fluted reamer in hole that has keyway or oil groove cut in itNever attempt to remove too much material (maximum = .010 in.)Frequently clear taper reamer and hole of chips
10To Ream Hole With a Straight Hand Reamer Check size of drilled hole ( in. smaller than finished hole size)Place end of reamer in hole and place tap wrench on square end of reamerRotate reamer clockwise to align with holeCheck reamer for squareness with workBrush cutting fluid over end of reamerRotate reamer slowly clockwise and apply downward pressure
12Advantages of Broaching Machining almost any irregular shape is possible (providing it is parallel to axis)Rapid: entire process usually in one passRoughing and finishing cuts combinedVariety of forms, internal or external, may be cut simultaneously and entire width of surface may be machined in one pass
13Cutting a Keyway With a Broach Keyways may be cut by hand quickly and accurately by means of broach set and arbor pressBroach set covers wide range of keywaysEquipment necessary to cut keywayBushing to suit hole sizeBroach size of keyway to be cutShims to increase depth of cut of broach
14Procedure for Cutting a Keyway With a Broach Determine keyway size requiredSelect proper broach, bushing and shimsPlace workpiece on arbor pressUse an opening on base smaller than opening in work so bushing properly supportedInsert bushing and broach into openingApply cutting fluid if workpiece is steel
15Check broach to be sure that it has started squarely in hole Press broach through workpieceMaintain constant pressure on arbor-press handleRemove broach, insert one shim and press broach through holeInsert second shim, if required, and press broach through againThis cuts keyway to proper depthRemove bushing, broach, and shims5. Check the broach to be sure that it has started squarely in the hole.
16LappingAbrading process used to remove minute amounts of metal from surfaceReasons for lappingIncrease wear life of partImprove accuracy and surface finishImprove surface flatnessProvide better seals and eliminate need for gasketsIntended to remove only about in.
17Lapping Abrasives Both natural and artificial abrasives used Flour of emery and fine powders made of silicon carbide or aluminum oxide used extensivelyUsed for rough lapping should be no coarser than 150 gritFine powders run up to 600 gritFine work uses diamond dust in paste form
18Flat Laps Close-grained cast iron laps used for flat surfaces Roughing operation (blocking down)Lapping plate scored with narrow grooves .500 in. apart both lengthwise and crosswise to form square or diamond patternFinish lapping done on smooth cast-iron plate
19Charging the Flat Lapping Plate Spread thin coating of abrasive powder over surface of platePress particles into surface of lap with hardened steel block or rollWhen surface charged, clean surface with varsol and examine for bright spotsUntil entire surface assumes gray appearance after it has been cleanedCharging the Flat Lapping Plate
20Lapping a Flat SurfacePlace a little varsol on finish-lapping plate that has been chargedPlace work on top of plate and gently push it back and forth over full surface of lap using irregular movementDo not stay in one spot!Continue this movement with light pressure until desired surface finish obtained
21Lapping: Precautions to Be Observed Do not stay in one area; cover full surface of the lapNever add fresh supply of loose abrasiveNever press too hard on work because lap will become stripped in placesAlways keep lap moist
22Internal LapsHoles accurately finished to size and smoothness by lappingMade of brass, copper, or leadThree typesLeadInternalAdjustable
26Charging and Using an Internal Lap Note: Before charging, lap should be running fit in hole.Sprinkle some lapping powder evenly on flat plateRoll lap over powder, to embed abrasive into surface of lapRemove excess powderMount lathe dog on end of lap
27Fit workpiece over end of lap Lab should not be wringing fit in hole of work and about 2.5 times length of workPlace some oil or varsol on lapMount lap and work between lathe centersSet machine to run at slow speed, 150 to 200 r/min for 1 in. diameterHold work securely and start machineRun work back and forth entire length11. Remove the work and rinse it in varsol to remove the abrasive and to bring it to room temperature.12. Gage the hole for size.Note: Always keep the lap moist and never add loose abrasive to the lap. Loose abrasive will cause the work to become bell-mouthed at the ends. If more abrasive is necessary, recharge the lap and adjust as required.
28Remove work and rinse it in varsol to remove abrasive and to bring to room temperature Gage hole for sizeNote: Keep lap moist and never add loose abrasive to lap. Loose abrasive will cause work to become bell-mouthed at ends. If more abrasive necessary, recharge lap and adjust as required.
29External Laps Used to finish outside of cylindrical workpieces May be several forms, however, basic design sameMade of cast iron or may have split brass bushing mounted inside by setscrewMust be some provision for adjusting lap
30Charging and Using an External Lap Mount workpiece in three-jaw chuck on lathe or drill pressAdjust lap until it is running fit on workGrip end of lap in viseSprinkle abrasive powder in holeWith hardened steel pin, roll abrasive evenly around inside surface of lapRemove excess lapping powder
31Place lap on workpiece. It should now be wringing fit. Set machine to run at slow speed (150 to 200 r/min for 1 in. diameter)Add some varsol to workpiece and lapHold lap securely and start machineMove lap back and forth along workAlways keep lap moistTo gage work, remove lap and clean workpiece with varsol