1. Drill Press Operations
Unit 44

2. Objectives Counterbore and countersink holes
Select and use the proper tap to thread a hole in a drill press
Use three methods to transfer hole locations

3. Counterboring
Operation of enlarging end of hole that has been drilled previously
Depth slightly greater than head of bolt, cap screw or pin it is to accommodate
Supplied in variety of styles
Each have pilot in end to keep tool in line with hole
Some interchangeable pilots to suit variety of holes

4. Procedure to Counterbore a Hole
Set up and fasten work securely
Drill proper size of hole in workpiece to suit body of pin or screw
Mount correct size of counterbore in drill press
Set drill press speed to approximately one-quarter that used for drilling
Bring counterbore close to work to see that the pilot turns freely in drilled hole
Start machine, apply cutting fluid and counterbore

5. Countersinking
Process of enlarging top end of hole to shape of cone to accommodate conical-shaped heads of fasteners
Head will be flush with or below surface
Countersinks available with various included angles
60º, 82º, 90º, 100º, 110º, and 120º

6. Countersinking
82º countersink used to enlarge top of hole so it will accommodate a flat-head machine screw
Holes to be threaded countersunk slightly larger than tap diameter
Speed is approximately 1/4th of drilling speed
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

7. Procedure to Countersink a Hole for a Machine Screw
Mount an 82º countersink in drill chuck
Adjust spindle speed to about ½ that used for drilling
Place workpiece on drill table
With spindle stopped, lower countersink into hole
Clamp work if necessary

8. If several holes to do, set depth stop
Raise countersink slightly, start machine, and feed countersink by hand until proper depth is reached.
Diameter checked by placing inverted screw in countersunk hole
If several holes to do, set depth stop
Countersink all holes to depth set on gage

9. Tapping Performed by hand or under power with tapping attachment
Done immediately after drilling operation
Hand taps
In sets containing taper, plug, bottoming tap
Machine taps
Designed to withstand torque required to thread hole and clear chips

10. Set of Hand Taps Taper Plug Bottoming
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

11. Types of Machine Taps Gun Stub-flute Spiral-flute
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

12. Fluteless Tap
Actually a forming tool used to produce internal threads in ductile material
Copper, brass, aluminum, and leaded steels
Fluteless tap
Lobes of the tap
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

13. Procedure to Tap a Hole by Hand in a Drill Press
Mount work on parallels with center-punch mark on work in line with spindle and clamp work securely to drill press table
Adjust drill press table height so drill may be removed after hole has been drilled without moving table or work
Center drill hole location

14. Drill hole to correct tap drill size for tap to be used
Mount stub center in drill chuck
Or remove drill chuck and mount special center in drill press spindle
Fasten suitable tap wrench on end of tap
Place tap in drilled hole, lower drill press spindle until center fits into center hole in tap shank
Turn tap wrench clockwise to start tap
Continue to tap hole, applying light pressure

15. Tapping Attachment
Mounted in a drill press spindle to rotate tap by power
Built-in friction clutch that drives tap clockwise when drill press spindle fed downward
Reversing mechanism to back tap out of hole
Two- , three-fluted machine or gun taps used for power
Ability to clear chips
Tapping speed ranges from 60 – 100 r/min

16. Three Common Methods of Transferring Hole Locations
Spotting with a twist drill
Using transfer punches
Using transfer screws
Regardless of which method, holes in existing part used as master, or guide, to transfer hole locations to another part.

17. Procedure to Spot with a Twist Drill
Remove burrs from mating surfaces on both parts
Align both parts accurately and clamp them together
Mount drill, same diameter as hole to be transferred, in drill press spindle

18. Start drill into hole of guide part and spot-drill second part
Never spot-drill deeper than diameter of drill
Spot-drill all holes to be transferred
Remove original part
Drill spotted holes to required diameter

19. Procedure to Use Transfer Punches
Remove burrs from mating surfaces on both parts
Align both parts accurately and clamp them together
Secure transfer punch of same diameter as hole to be transferred

20. Place punch in hole and lightly strike it with hammer to mark hole location
Use correct size of transfer punch on all holes to be transferred
Remove original part
Use divider to lay out proof circles for holes to be drilled
With center punch, deepen existing transfer-punch marks
Use proper method to drill holes accurately

21. Transfer Screws Used to transfer location of threaded holes
Hardened and sharpened to a point
Two flats ground on point to allow screws to be threaded into hole with small wrench
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

22. Procedure to Use Transfer Screws
Remove all burrs from mating surfaces
Thread transfer screws into holes to be transferred (points extend .030 in.)
Align both parts accurately and sharply strike one part with hammer
Remove original part, deepen marks left by transfer screws with center punch
Drill all holes to required size

23. Drill Jigs
Used to drill holes to an exact location in many identical parts
Used to save layout time
Produces holes accurately and economically
Hardened drill jig bushings guide drill
Multispindle drill (or gang) press
Two or more different sizes of holes in same part (drill jig passes from one spindle to next)

24. Advantages of Using a Drill Jig
Layout time is eliminated
Each part quickly and accurately aligned
Part held in position by clamping mechanism
Drill jig bushings provide guide for drill
Hole locations in each part will be exactly the same
Unskilled labor can be used