1. Finishing Processes - Reaming, Broaching, and Lapping
Unit 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

3. Hand Cutting Tools Reamers Broaches Lapping
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

4. Solid Hand Reamer Made of carbon steel or high-speed steel
Available in inch sizes from in.
Metric from 1 – 26 mm in diameter
Not adjustable and may have straight or helical flutes
Should not be used on work with keyway or any other interruption (chatter and poor finish)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

5. Expansion Hand Reamer
Designed to permit adjustment of approximately .006 in. above nominal diameter
Hollow and has slots along length of cutting section
Tapered threaded plug fitted into end of reamer provides for limited expansion
Cutting end of reamer ground to slight taper
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

6. Adjustable Hand Reamer
Has tapered slots along entire length of body
Inner edges of cutting blades have corresponding taper so blades remain parallel for any settings
Adjusted to size by upper and lower adjusting nuts
Blades have adjustment range of 132 in. on smaller reamers to almost 516 in. on larger ones
Manufactured in sizes ¼ to 3 in. in diameter
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7. Taper Reamer Used to finish tapered holes accurately and smoothly
Made with either spiral or straight teeth
Spiral-flute superior to straight due to shearing action and reduced chatter
Roughing reamer
Nicks ground at intervals along teeth
Used for more rapid removal of surplus metal
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8. Finishing Taper Reamer
Used after roughing reamer to finish hole smoothly and to size
Either straight or left-hand spiral flutes
Designed to remove only small amount of metal (about .010 in from hole)
Do not clear themselves readily
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

9. Reaming Precautions
Never turn reamer backward (counterclockwise), it will dull teeth
Use cutting lubricant where required
Always use helical-fluted reamer in hole that has keyway or oil groove cut in it
Never attempt to remove too much material (maximum = .010 in.)
Frequently clear taper reamer and hole of chips

10. To 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 reamer
Rotate reamer clockwise to align with hole
Check reamer for squareness with work
Brush cutting fluid over end of reamer
Rotate reamer slowly clockwise and apply downward pressure

11. Broaching
Process in which special tapered multitoothed cutter forced through an opening or along outside piece of work to enlarge or change shape of hole
First used for internal shapes (keyways, splines)
Cutting action performed by series of successive teeth
Each protrude .003 in. farther than preceding tooth
Last three teeth same depth and provide finish cut
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12. Advantages of Broaching
Machining almost any irregular shape is possible (providing it is parallel to axis)
Rapid: entire process usually in one pass
Roughing and finishing cuts combined
Variety of forms, internal or external, may be cut simultaneously and entire width of surface may be machined in one pass

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

14. Procedure for Cutting a Keyway With a Broach
Determine keyway size required
Select proper broach, bushing and shims
Place workpiece on arbor press
Use an opening on base smaller than opening in work so bushing properly supported
Insert bushing and broach into opening
Apply cutting fluid if workpiece is steel

15. Check broach to be sure that it has started squarely in hole
Press broach through workpiece
Maintain constant pressure on arbor-press handle
Remove broach, insert one shim and press broach through hole
Insert second shim, if required, and press broach through again
This cuts keyway to proper depth
Remove bushing, broach, and shims
5. Check the broach to be sure that it has started squarely in the hole.

16. Lapping
Abrading process used to remove minute amounts of metal from surface
Reasons for lapping
Increase wear life of part
Improve accuracy and surface finish
Improve surface flatness
Provide better seals and eliminate need for gaskets
Intended to remove only about in.

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

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

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
Charging the Flat Lapping Plate

20. Lapping a Flat Surface
Place a little varsol on finish-lapping plate that has been charged
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!
Continue this movement with light pressure until desired surface finish obtained

21. Lapping: Precautions to Be Observed
Do not stay in one area; cover full surface of the lap
Never add fresh supply of loose abrasive
Never press too hard on work because lap will become stripped in places
Always keep lap moist

22. Internal Laps
Holes accurately finished to size and smoothness by lapping
Made of brass, copper, or lead
Three types
Lead
Internal
Adjustable

23. Lead Lap
Made by pouring lead around tapered mandrel that has groove along length
Turned to running fit into hole
Sometimes slit on outside to trap loose abrasive
Adjust by lightly tapping large end of mandrel with soft block
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

24. Internal Lap May be made of copper, brass or cast iron
Threaded-taper plug fits into end of lap
Slit for almost its entire length
Lap diameter may be adjusted by threaded-taper plug
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25. Adjustable Lap May be made from copper or brass
Split for almost full length, but both ends remain solid
Slight adjustment provided by means of two setscrew in center section
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

26. Charging and Using an Internal Lap
Note: Before charging, lap should be running fit in hole.
Sprinkle some lapping powder evenly on flat plate
Roll lap over powder, to embed abrasive into surface of lap
Remove excess powder
Mount lathe dog on end of lap

27. Fit workpiece over end of lap
Lab should not be wringing fit in hole of work and about 2.5 times length of work
Place some oil or varsol on lap
Mount lap and work between lathe centers
Set machine to run at slow speed, 150 to 200 r/min for 1 in. diameter
Hold work securely and start machine
Run work back and forth entire length
11. 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.

28. Remove work and rinse it in varsol to remove abrasive and to bring to room temperature
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.

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

30. Charging and Using an External Lap
Mount workpiece in three-jaw chuck on lathe or drill press
Adjust lap until it is running fit on work
Grip end of lap in vise
Sprinkle abrasive powder in hole
With hardened steel pin, roll abrasive evenly around inside surface of lap
Remove excess lapping powder

31. Place 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 lap
Hold lap securely and start machine
Move lap back and forth along work
Always keep lap moist
To gage work, remove lap and clean workpiece with varsol