1. Special Milling Operations
Unit 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

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

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

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

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

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

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

9. To Center Rotary Table with Vertical Mill Spindle
Square vertical head with machine table
Mount rotary table on milling machine
Place test plug in center hole
Mount indicator with grasshopper leg in machine spindle
With indicator just clearing top of test plug, rotate machine spindle by hand align plug with spindle

10. To Center Rotary Table with Vertical Mill Spindle
Bring indicator into contact with diameter of plug and rotate spindle by hand
Adjust machine table by longitudinal and crossfeed handles until dial indicator registers no movement
Lock machine table and saddle, recheck alignment
Readjust if necessary

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

12. Method to Center Workpiece on Rotary Table (no plug)
Align rotary table with vertical head spindle
Lightly clamp workpiece to rotary table in approximate center
Do not move crossfeed or longitudinal feed
Disengage rotary table worm mechanism
Mount indicator in machine spindle or on milling machine table

13. Clamp workpiece tightly and recheck accuracy of setup
Bring indicator into contact with surface to be indicated and revolve rotary table by hand
With soft metal bar, tap work until no movement registered on indicator in complete revolution of table
Tap away from indicator movement
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.

14. Radius Milling Procedure
Align vertical milling machine spindle at 90º to table
Mount circular milling attachment
Center rotary table with machine spindle
Use test plug in table and dial indicator in spindle
Set longitudinal feed dials and crossfeed dial to zero

15. Mount work on rotary table
Align center of radial cuts with table center
Can use special arbor or wiggler
Move either crossfeed or longitudinal feed an amount equal to radius required
Lock both table and saddle
Mount proper end mill
Rotate work (using handwheel) to starting point of cut
Set depth of cut and machine slot to size

16. Milling a T-Slot Procedure
Consult handbook for T-slot dimensions
Lay out position of T-slot
Square vertical milling machine spindle with machine table
Mount work on milling machine
Align vise or slot if clamped with table

17. Machine center slot to proper depth of T-slot, using end mill
Mount an end mill having diameter slightly larger than diameter of bolt body
Machine center slot to proper depth of T-slot, using end mill
Remove end mill, mount proper T-slot cutter
Set T-slot cutter depth to bottom of slot
Machine lower part of slot

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

19. Procedure for Milling an Internal Dovetail
Refer to handbook for method
Check measurements of workpiece in which dovetail is to be cut
Remove all burrs
Lay out position of dovetail
Mount workpiece in vise and clamp on rotary table (long work – bolt to table)

20. Mount end mill of a diameter narrower than center section of dovetail
Indicate side of workpiece or slot layout to see that it is parallel to line of table travel
Mount end mill of a diameter narrower than center section of dovetail
Start end mill and touch up to side of work, after checking cutter rotation
Set crossfeed dial to zero
Move work over until end mill in center of dovetail
Distance from side of workpiece to center of dovetail plus half diameter of cutter

21. Lock saddle in position and set crossfeed dial to zero
Touch edge of cutter to top of work
Move work clear of cutter and set depth of cut
Lock knee in position
Depth of slot should be .030 to 0.50 in. deeper than bottom of dovetail
Mill channel to width of cutter

22. Move work over amount equal to half difference between machined slot size and size of dovetail at top
Take finish cut along one side of work
Check width of slot
Move work over to finished width of top of dovetail (Check for backlash)
Cut second side and check width of slot
Return saddle to zero

23. Set depth for roughing cut
Mount dovetail cutter
Set depth for roughing cut
Should be about .005 to .010 in. less than finish depth
Calculate width of dovetail at bottom
Move work over .010 in. less than finished size of this side
Note readings on crossfeed dial
Rough out angle on first side

24. Move work over to other side the same amount from centerline and rough-cut other side
Set cutter to proper depth
Machine bottom surface (both sides) of dovetail to finished depth
Using two rods, measure dovetail for size

25. Take finish cut on one side
Move table over half the difference between rough dovetail and finished size
Check for backlash
Take finish cut on one side
Move table over required amount, and finish other side
Check finish size of dovetail
Note: If work mounted centrally on rotary table, possible to rotate work a half-turn (180º) after 18 and take same cuts on each side of block for each successive step.

26. Procedure to Mill an External Dovetail
Center cutter over dovetail position
Remove as much material as possible from each side of external dovetail
Cut to largest size of dovetail
Mount dovetail cutter, and center it with workpiece
Move work over ½ width of dovetail plus half diameter of cutter
Allow in. for finish cut

27. Take roughing cut
Move work over equal amount to other side of centerline, taking up backlash
Rough-cut second side
Adjust work over, and take finish cut on one side
Measure dovetail using two rods
Adjust for finish cut on second side and take this cut
Measure width of finished dovetail

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

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 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 mm

30. To Position Milling Machine Table Using Measuring Rods
Set spindle to edge of work
Clean trough and ends of stop rods and indicator rods
Check indicator for free operation
Place required number of rods in trough to take up space between stop rod and indicator rod

31. Adjust micrometer until extended enough to cause indicator needle to move half-turn
Lock table
Set indicator bezel to zero
Increase rod and micrometer buildup by length of measurement between side of workpiece and hole location
Move table along more than this required distance

32. Insert rods and micrometer head
Move table back until needle moves half-turn and registers zero
Lock table
Recheck setting and adjust if necessary

33. Digital Readout Boxes Electronically controlled measuring devices
Mounted on table and saddle
Indicate table travel to accuracy of .005 or 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

34. Vernier Scale May be used with milling machine
Mounted adjacent to feed screw collars
Permits reading in in or mm.
Setting must be made in one direction only in order to remove backlash
Note: Can position holes without scales by using the graduated feed collars. This method not as accurate.

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

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

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