25-2 Objectives Identify and explain the purpose of several types of hand reamers Ream a hole accurately with a hand reamer Cut a keyway in a workpiece using a broach and arbor press Lap a hole or an external diameter of a workpiece to size and finish
25-3 Hand Cutting Tools Reamers –Used to bring hole to size and produce good finish Broaches –Used with arbor press to produce special shapes in workpiece –Multi-tooth tool forced through hole Lapping –Where very fine abrasive powder, embedded in tool is used to remove minute amounts of material from surface
25-9 Reaming Precautions 1.Never turn reamer backward (counterclockwise), it will dull teeth 2.Use cutting lubricant where required 3.Always use helical-fluted reamer in hole that has keyway or oil groove cut in it 4.Never attempt to remove too much material (maximum =.010 in.) 5.Frequently clear taper reamer and hole of chips
25-10 To Ream Hole With a Straight Hand Reamer 1.Check size of drilled hole ( in. smaller than finished hole size) 2.Place end of reamer in hole and place tap wrench on square end of reamer 3.Rotate reamer clockwise to align with hole 4.Check reamer for squareness with work 5.Brush cutting fluid over end of reamer 6.Rotate reamer slowly clockwise and apply downward pressure
25-12 Advantages of Broaching 1.Machining almost any irregular shape is possible (providing it is parallel to axis) 2.Rapid: entire process usually in one pass 3.Roughing and finishing cuts combined 4.Variety of forms, internal or external, may be cut simultaneously and entire width of surface may be machined in one pass
25-13 Cutting a Keyway With a Broach Keyways may be cut by hand quickly and accurately by means of broach set and arbor press Broach set covers wide range of keyways Equipment necessary to cut keyway –Bushing to suit hole size –Broach size of keyway to be cut –Shims to increase depth of cut of broach
25-14 Procedure for Cutting a Keyway With a Broach 1.Determine keyway size required 2.Select proper broach, bushing and shims 3.Place workpiece on arbor press Use an opening on base smaller than opening in work so bushing properly supported 4.Insert bushing and broach into opening Apply cutting fluid if workpiece is steel
Check broach to be sure that it has started squarely in hole 6.Press broach through workpiece Maintain constant pressure on arbor-press handle 7.Remove broach, insert one shim and press broach through hole 8.Insert second shim, if required, and press broach through again This cuts keyway to proper depth 9.Remove bushing, broach, and shims
25-16 Lapping Abrading process used to remove minute amounts of metal from surface Reasons for lapping 1.Increase wear life of part 2.Improve accuracy and surface finish 3.Improve surface flatness 4.Provide better seals and eliminate need for gaskets Intended to remove only about.0005 in.
25-17 Lapping Abrasives Both natural and artificial abrasives used Flour of emery and fine powders made of silicon carbide or aluminum oxide used extensively Used for rough lapping should be no coarser than 150 grit Fine powders run up to 600 grit Fine work uses diamond dust in paste form
25-18 Flat 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 pattern Finish lapping done on smooth cast-iron plate
25-19 Charging the Flat Lapping Plate Spread thin coating of abrasive powder over surface of plate Press particles into surface of lap with hardened steel block or roll When surface charged, clean surface with varsol and examine for bright spots –Until entire surface assumes gray appearance after it has been cleaned
25-20 Lapping a Flat Surface 1.Place a little varsol on finish-lapping plate that has been charged 2.Place work on top of plate and gently push it back and forth over full surface of lap using irregular movement –Do not stay in one spot! 3.Continue this movement with light pressure until desired surface finish obtained
25-21 Lapping: Precautions to Be Observed 1.Do not stay in one area; cover full surface of the lap 2.Never add fresh supply of loose abrasive 3.Never press too hard on work because lap will become stripped in places 4.Always keep lap moist
25-22 Internal Laps Holes accurately finished to size and smoothness by lapping Made of brass, copper, or lead Three types –Lead –Internal –Adjustable
25-26 Charging and Using an Internal Lap 1.Sprinkle some lapping powder evenly on flat plate 2.Roll lap over powder, to embed abrasive into surface of lap 3.Remove excess powder 4.Mount lathe dog on end of lap Note: Before charging, lap should be running fit in hole.
Fit workpiece over end of lap Lab should not be wringing fit in hole of work and about 2.5 times length of work 6.Place some oil or varsol on lap 7.Mount lap and work between lathe centers 8.Set machine to run at slow speed, 150 to 200 r/min for 1 in. diameter 9.Hold work securely and start machine 10.Run work back and forth entire length
Remove work and rinse it in varsol to remove abrasive and to bring to room temperature 12.Gage hole for size Note: 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.
25-29 External Laps Used to finish outside of cylindrical workpieces May be several forms, however, basic design same Made of cast iron or may have split brass bushing mounted inside by setscrew Must be some provision for adjusting lap
25-30 Charging and Using an External Lap 1.Mount workpiece in three-jaw chuck on lathe or drill press 2.Adjust lap until it is running fit on work 3.Grip end of lap in vise 4.Sprinkle abrasive powder in hole 5.With hardened steel pin, roll abrasive evenly around inside surface of lap 6.Remove excess lapping powder
Place lap on workpiece. It should now be wringing fit. 8.Set machine to run at slow speed (150 to 200 r/min for 1 in. diameter) 9.Add some varsol to workpiece and lap 10.Hold lap securely and start machine 11.Move lap back and forth along work Always keep lap moist 12.To gage work, remove lap and clean workpiece with varsol