This document discusses various drilling and tapping operations that can be performed on a drill press, including: - Counterboring and countersinking holes to specific shapes and depths. - Proper tapping techniques using hand taps or a tapping attachment, including selecting the correct tap and drilling the correctly sized pilot hole. - Three methods for transferring hole locations between parts: spot drilling with a twist drill, using transfer punches, or using transfer screws. - The use of drill jigs to quickly and accurately drill multiple identical parts by guiding the drill and eliminating layout time.

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Permission required for reproduction or display.
PowerPoint to accompany
Krar • Gill • Smid
Technology of Machine Tools
6th Edition
Drill Press
Operations
Unit 44

2. 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. 44-3
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. 44-4
Procedure to
Counterbore a Hole
1. Set up and fasten work securely
2. Drill proper size of hole in workpiece to suit body
of pin or screw
3. Mount correct size of counterbore in drill press
4. Set drill press speed to approximately one-quarter
that used for drilling
5. Bring counterbore close to work to see that the
pilot turns freely in drilled hole
6. Start machine, apply cutting fluid and counterbore

5. 44-5
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. 44-6
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
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7. 44-7
Procedure to Countersink a Hole
for a Machine Screw
1. Mount an 82º countersink in drill chuck
2. Adjust spindle speed to about ½ that used
for drilling
3. Place workpiece on drill table
4. With spindle stopped, lower countersink
into hole
• Clamp work if necessary

8. 44-8
5. Raise countersink slightly, start machine,
and feed countersink by hand until proper
depth is reached.
• Diameter checked by placing inverted screw
in countersunk hole
6. If several holes to
do, set depth stop
7. Countersink all
holes to depth
set on gage

9. 44-9
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. 44-10
Set of Hand Taps
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Taper
Plug
Bottoming

11. 44-11
Types of Machine Taps
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Gun
Stub-flute
Spiral-flute

12. 44-12
Fluteless Tap
• Actually a forming tool used to produce
internal threads in ductile material
– Copper, brass, aluminum, and leaded steels
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Fluteless tap
Lobes of the tap

13. 44-13
Procedure to Tap a Hole by
Hand in a Drill Press
1. Mount work on parallels with center-
punch mark on work in line with spindle
and clamp work securely to drill press
table
2. Adjust drill press table height so drill may
be removed after hole has been drilled
without moving table or work
3. Center drill hole location

14. 44-14
4. Drill hole to correct tap drill size for
tap to be used
5. Mount stub center in drill chuck
• Or remove drill chuck and mount special
center in drill press spindle
6. Fasten suitable tap wrench on end of tap
7. Place tap in drilled hole, lower drill press
spindle until center fits into center hole
in tap shank
8. Turn tap wrench clockwise to start tap
9. Continue to tap hole, applying light pressure

15. 44-15
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. 44-16
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. 44-17
Procedure to Spot
with a Twist Drill
1. Remove burrs from mating surfaces on
both parts
2. Align both parts accurately and clamp
them together
3. Mount drill, same diameter as hole to be
transferred, in drill press spindle

18. 44-18
4. Start drill into hole of guide part and spot-
drill second part
• Never spot-drill deeper than diameter of drill
5. Spot-drill all holes to be transferred
6. Remove original part
7. Drill spotted holes to required diameter

19. 44-19
Procedure to Use
Transfer Punches
1. Remove burrs from mating surfaces on
both parts
2. Align both parts accurately and clamp
them together
3. Secure transfer punch of same diameter as
hole to be transferred

20. 44-20
4. Place punch in hole and lightly strike it
with hammer to mark hole location
5. Use correct size of transfer punch on all
holes to be transferred
6. Remove original part
7. Use divider to lay out proof circles for
holes to be drilled
8. With center punch, deepen existing
transfer-punch marks
9. Use proper method to drill holes accurately

21. 44-21
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
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22. 44-22
Procedure to
Use Transfer Screws
1. Remove all burrs from mating surfaces
2. Thread transfer screws into holes to be
transferred (points extend .030 in.)
3. Align both parts accurately and sharply
strike one part with hammer
4. Remove original part, deepen marks left
by transfer screws with center punch
5. Drill all holes to required size

23. 44-23
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. 44-24
Advantages of Using a Drill Jig
1. Layout time is eliminated
2. Each part quickly and accurately aligned
3. Part held in position by clamping
mechanism
4. Drill jig bushings provide guide for drill
5. Hole locations in each part will be exactly
the same
6. Unskilled labor can be used