Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

PowerPoint to accompany

Krar • Gill • Smid

Technology of Machine Tools6th Edition

Special Milling Operations Unit 63

63-2

Objectives • Set up and use the rotary table to

mill a circular slot• Set up and mill internal and

external dovetails• Jig bore holes on a vertical mill

63-3

Vertical Milling Machine

• Versatility increased using specially shaped cutters and accessories

• Rotary table accessory permits milling of radii and circular slots

• Boring head in spindle and measuring rods on tale allow accurate jig boring of holes

63-4

The Rotary Table• Circular milling attachment• Used on plain universal vertical milling

machines and slotters• Provide rotary motion to workpiece• Cut radii, circular grooves and circular

sections• Two types

– hand feed and power feed

63-5

Rotary Table Construction• Base bolted to milling machine table• Rotary table fits into base• Worm gear on bottom of rotary table• Worm shaft mounted in base and meshes with

and drives worm gear• Handwheel mounted on outer end of worm

shaft– Vernier scale on collar permits setting to

within 2 minutes of a degree

63-6

Rotary Table Construction

• T-slots cut into top surface to permit clamping of work

• Hole in center of table accommodates test plugs for easy centering of table with machine spindle

• Some have indexing attachment instead of handwheel

63-7

Indexing Attachment• Serves same purpose as handwheel• Permits indexing of work with dividing head

accuracy– Worm and wormwheel ratio not necessarily 40:1

• Other common ratios: 72:1, 80:1, 90:1, 120:1

required divisions ofnumber elin wormwhe teeth ofnumber

Indexing

Example: Calculate indexing for 5 equally spaced holes on a circular plate using a rotary table with an 80:1 ration

turns165

80

63-8

Rotary Table with Powerfeed

• Worm shaft connected to milling machine lead screw drive gear by special shaft and end gear train

• Rate of rotation controlled by feed mechanism of milling machine– Operator control by automatic feed lever or

handwheel• Suited for production work and continuous

milling of numerous small, identical parts

63-9

To Center Rotary Table with Vertical Mill Spindle

1. Square vertical head with machine table2. Mount rotary table on milling machine3. Place test plug in center hole4. Mount indicator with grasshopper leg in

machine spindle5. With indicator just clearing top of test

plug, rotate machine spindle by handalign plug with spindle

63-10

To Center Rotary Table with Vertical Mill Spindle

6. Bring indicator into contact with diameter of plug and rotate spindle by hand

7. Adjust machine table by longitudinal and crossfeed handles until dial indicator registers no movement

8. Lock machine table and saddle, recheck alignment

9. Readjust if necessary

63-11

Using Special Plugs to Center

• Problem: work on several identical workpieces that have machined hole in center - need to align– Special plug made to fit center hold of

workpiece and hole in rotary table– Once machine spindle aligned with table, each

succeeding piece can be aligned quickly and accurately by placing over plug

63-12

Method to Center Workpiece on Rotary Table (no plug)

1. Align rotary table with vertical head spindle

2. Lightly clamp workpiece to rotary table in approximate center

• Do not move crossfeed or longitudinal feed3. Disengage rotary table worm mechanism4. Mount indicator in machine spindle or on

milling machine table

63-13

5. Bring indicator into contact with surface to be indicated and revolve rotary table by hand

6. With soft metal bar, tap work until no movement registered on indicator in complete revolution of table

• Tap away from indicator movement

7. Clamp workpiece tightly and recheck accuracy of setup

Note: If center-punch mark must be aligned, wiggler mounted in milling machine spindle instead of indicator.

63-14

Radius Milling Procedure

1. Align vertical milling machine spindle at 90º to table

2. Mount circular milling attachment3. Center rotary table with machine spindle

• Use test plug in table and dial indicator in spindle

4. Set longitudinal feed dials and crossfeed dial to zero

63-15

5. Mount work on rotary table• Align center of radial cuts with table center

• Can use special arbor or wiggler

6. Move either crossfeed or longitudinal feed an amount equal to radius required

7. Lock both table and saddle8. Mount proper end mill9. Rotate work (using handwheel) to starting

point of cut10. Set depth of cut and machine slot to size

63-16

Milling a T-Slot Procedure

1. Consult handbook for T-slot dimensions2. Lay out position of T-slot3. Square vertical milling machine spindle

with machine table4. Mount work on milling machine

• Align vise or slot if clamped with table

63-17

5. Mount an end mill having diameter slightly larger than diameter of bolt body

6. Machine center slot to proper depth of T-slot, using end mill

7. Remove end mill, mount proper T-slot cutter

8. Set T-slot cutter depth to bottom of slot9. Machine lower part of slot

63-18

Milling Dovetails

• Used to permit reciprocating motion between two elements of a machine

• Composed of external or internal part• Adjusted by means of a gib• Machines on vertical milling machine or

horizontal mill with vertical mill attachment• Dovetail cutter

– Special single-angle end mill type of cutter ground to angle of dovetail required

63-19

Procedure for Milling anInternal Dovetail

1. Refer to handbook for method2. Check measurements of workpiece in

which dovetail is to be cut• Remove all burrs

3. Lay out position of dovetail4. Mount workpiece in vise and clamp on

rotary table (long work – bolt to table)

63-20

5. Indicate side of workpiece or slot layout to see that it is parallel to line of table travel

6. Mount end mill of a diameter narrower than center section of dovetail

7. Start end mill and touch up to side of work, after checking cutter rotation

8. Set crossfeed dial to zero9. Move work over until end mill in center of

dovetail• Distance from side of workpiece to center of

dovetail plus half diameter of cutter

63-21

10. Lock saddle in position and set crossfeed dial to zero

11. Touch edge of cutter to top of work12. Move work clear of cutter and set depth

of cut1. Lock knee in position2. Depth of slot should be .030 to 0.50 in.

deeper than bottom of dovetail

13. Mill channel to width of cutter

63-22

14. Move work over amount equal to half difference between machined slot size and size of dovetail at top

15. Take finish cut along one side of work16. Check width of slot17. Move work over to finished width of top

of dovetail (Check for backlash)18. Cut second side and check width of slot19. Return saddle to zero

63-23

20. Mount dovetail cutter21. Set depth for roughing cut

1. Should be about .005 to .010 in. less than finish depth

22. Calculate width of dovetail at bottom23. Move work over .010 in. less than

finished size of this side1. Note readings on crossfeed dial

24. Rough out angle on first side

63-24

25. Move work over to other side the same amount from centerline and rough-cut other side

26. Set cutter to proper depth

27. Machine bottom surface (both sides) of dovetail to finished depth

28. Using two rods, measure dovetail for size

63-25

29. Move table over half the difference between rough dovetail and finished size

• Check for backlash

30. Take finish cut on one side31. Move table over required amount, and

finish other side32. Check finish size of dovetailNote: If work mounted centrally on rotary table, possible torotate work a half-turn (180º) after 18 and take same cuts oneach side of block for each successive step.

63-26

Procedure to Mill an External Dovetail

1. Center cutter over dovetail position2. Remove as much material as possible

from each side of external dovetail• Cut to largest size of dovetail

3. Mount dovetail cutter, and center it with workpiece

4. Move work over ½ width of dovetail plus half diameter of cutter

• Allow 0.010 in. for finish cut

63-27

5. Take roughing cut6. Move work over equal amount to other

side of centerline, taking up backlash7. Rough-cut second side8. Adjust work over, and take finish cut on

one side9. Measure dovetail using two rods10. Adjust for finish cut on second side and

take this cut11. Measure width of finished dovetail

63-28

Jig Boring on a Vertical Milling Machine

• Vertical milling machine does not have same lead screw accuracy as jig borer– Must have some external measuring system– Measuring rods and dial indicators, vernier

scale, optical measure devices• Measuring rods come in sets

– Both inch precision and metric precision

63-29

Measuring Rod Sets• Inch precision end-measuring rods

– Supplied in sets of 11 rods hardened– Two micrometer heads capable of measuring 4-5

in to accuracy of .0001 in.• One for longitudinal settings and other for transverse

– Lengths of rods: 1, 2, 6 and 12 in rods• Metric precision end-measuring rods

– Same set up as inch rods only in mm– Accuracy of 0.002 mm

63-30

To Position Milling Machine Table Using Measuring Rods

1. Set spindle to edge of work2. Clean trough and ends of stop rods and

indicator rods3. Check indicator for free operation4. Place required number of rods in trough to

take up space between stop rod and indicator rod

63-31

5. Adjust micrometer until extended enough to cause indicator needle to move half-turn

6. Lock table7. Set indicator bezel to zero8. Increase rod and micrometer buildup by

length of measurement between side of workpiece and hole location

9. Move table along more than this required distance

63-32

10. Insert rods and micrometer head

11. Move table back until needle moves half-turn and registers zero

12. Lock table

13. Recheck setting and adjust if necessary

63-33

Digital Readout Boxes• Electronically controlled measuring devices

– Mounted on table and saddle– Indicate table travel to accuracy of .005

or .0001 in.• Digital readout display

– Indicates distance traveled through series of numbers visible

• Permits quick and accurate setting of machine table in both X and Y axes

63-34

Vernier Scale

• May be used with milling machine• Mounted adjacent to feed screw collars• Permits reading in .0001 in or 0.002 mm.• Setting must be made in one direction only

in order to remove backlash

Note: Can position holes without scales by using thegraduated feed collars. This method not as accurate.

63-35

Vertical Milling Machine Attachments

• Rack milling attachment– Permits machining of racks and broaches on

vertical mill• Slotting attachment

– Fitted to back end of overarm (180º rotation)– Operates independently of machine drive– Transmits reciprocating motion to single-

pointed tool by means of motor-driven eccentric– Used for cutting keyways and slotting out small

blanking dies

63-36

Die Sinking• One important application of vertical milling

machine• Dies used in drop forging and die casting have

impressions or cavities cut into them by die sinking

• Generally done by hand control of machine• Followed by considerable filing and polishing• Machine equipped with tracer head

63-37

Tracer-Controlled Machine

• Form of master transferred to workpiece by hydraulic tracer unit actuated by stylus – Contacts master and moves cutter up or down

with vertical or side travel of stylus• Work and master fastened to table and

travel at same rate• Some machines equipped with ratio devices