How
to Drill a Hole Where You Want It
Last updated on
Tuesday, September 19, 2023 08:43:36 PM
Mountain US Time Zone
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Scribing,
Center Punching,
Drilling,
Countersinks,
How to
Drill the Center of
a Rod,
Edge Finder,
Drilling a Rod,
General Deburring Tools,
Edge Deburring,
Corner
Deburring
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Cutting Speeds & Feeds for Drills
Some years
ago, I was
making two simple
T-brackets for my Taig lathe's lead screw subassembly.
The mating clearance & tapped holes were not quite aligned &
it was
frustrating. I recounted my difficulties to a tool &
die maker friend. He gave me the
following tips on how
to drill a hole
so it ends up where you want it to be
located,
instead of thousandths of an inch off.
The example shown
below is part of a
bracket used to mount the
Taig
Mill DRO.
Drilled holes are for clearance or
tapping.
The resulting hole size
can be larger than the labeled
drill bit
size & may not be perfectly round. Precision holes
are either
reamed,
bored, or
precision ground.
Scribing
A
granite surface plate
&
height gauge with a carbide
scribe
are essential. This surface plate is
+/-0.0001".
The larger the plate, the easier it is to use.
A good
height gauge will easily layout scribed lines to 0.0005".
If needed, higher accuracy can be achieved using
gauge blocks to set the
height.
Coat the
part's surface with
red or blue
layout fluid to make the scribe marks easier
to see. Place a precision block behind the smaller
parts.
Take care to not hit the scribe against the hardened
steel block as it might
chip the brittle, expensive carbide tip.
Grade A accuracy is +/- 0.000075"
Grade B accuracy is +/- 0.000150"
Granite Surface Plates checked using an
autocollimator for
accuracy
assurance to meet or exceed
Federal Specification GGG-P-463c.
Includes a Certificate of Inspection.
Center Punching
An
automatic center punch is helpful because
it allows you to
concentrate on locating the tip.
A
sharp center punch tip is very important. Feel
the intersecting scribe
marks with the tip & punch it.
One way is to hold the tip at an angle, draw it along
the scribed line until you
feel the intersecting marks,
pivot to vertical & punch.
If a punch mark is off,
it can be moved by angling & re-punching, as needed.
The depth of the punch mark can be varied
as detailed in the
center-punch section.
Starrett 18AA Center Punch
Drilling
Next, use a sharp, #2
center drill bit because it has a small
point plus it is
short & is much stiffer than a jobber drill
bit.
A drop of cutting fluid is helpful. Let the work piece float & the
turning center drill
bit tip will locate (grab) the punch mark.
Make an
adjustable brass or
aluminium stop
that fits into the table slot to keep
parts from turning.
Be sure to lock the drill press column & table.
Use sharp
drill bits with cutting fluid & clear the chips
out
of the hole,
often.
Clamp the piece after starting the hole.
If a large hole is being drilled, consider drilling a
smaller one first, as a
drill bit will tend to follow a hole.
Using a mill setup with its
fine down feed is the best
way to drill brass or almost anything else for that matter.
Beware of drilling in brass; it is soft & a standard
118 deg
drill bit will grab the piece spinning it plus a small vise.
Lock the drill press table & clamp the work piece.
Feed the drill in slowly
& clear the chips often.
One can also use a bit with a larger drill point angle (e.g.,
135 degrees) for
softer materials.
See
drill bit geometries.
Countersinks
Chamfer -
a cut that is made in material, usually at a 45 deg angle to
the adjacent principal faces.
Bevel -
usually larger, slanted surface but sometimes used interchangably
with chamfer.
Countersink
- a conical hole cut into a manufactured object, or the cutter
used to cut such a hole.
A common use is to allow the head of a
countersunk bolt, screw or rivet, when
placed in the hole, to
sit flush with or below the surface of the surrounding material.
Counterbore
- a cylindrical, flat-bottomed hole that enlarges another
coaxial hole, or the cutter
used to create such a hole. A counterbore hole
is typically used when a
fastener, such as a socket head cap
screw, is required to sit flush with
or below the level of a
workpiece's surface.
Zero-flute countersinks.
They can be sharpened
from inside the hole with a
fine round stone.
Different
countersink angles to match bolt head.
100 degs & above
are good for thin sheet metal.
Examples of counterbored, chamfered,
countersunk & reamed holes
plus milled beveled edges.
Bevel types, depicted.
Chamfer,
countersink,
counterbore as needed;
don't leave
sharp edges or corners
anywhere on the
part including holes.
Weldon, no chatter zero-flute bits
work very well for both chamfering & countersinking.
India (red) or Arkansas (white) stones are good for
removing burrs & are superior to a file.
The stones clog
with metal but they can be cleaned with solvent.
The layout die is removed with 0000 steel wool or solvent.
A
CNC or DRO-equipped mill can perform precision
layout & drilling but
often I do not
want to
setup
the mill for a few holes.
These methods work well
on a drill press & can be adapted for use on a mill.
The USA manufactured
countersinks are
superior to most import counterparts.
KEO,
Weldon,
M.A. Ford, &
Irwin are all excellent countersinks.
60 deg, 82 deg, & 90 deg
zero-flute countersink sets.
How to
Drill the Center of
a Rod
These techniques also apply to end mills and/or any
other type of parts.
First, indicate the part with any
edge finder, zero the
DRO, lift the finder,
compensate
for the indicator radius (0.100" shown) & then
zero
the DRO, again.
Indicate the other part edges/axes,
as needed. The spindle is turning at ~1000
RPM.
Edge Finder
Drilling a Rod
Measure the part with a
micrometer or caliper.
The
example rod is 0.500" diameter so the center drill bit is moved
0.250"
on the Y-axis.
Center drill bits are stiff (low flex) &
have a small tip allowing a good start
on a curved surface.
A long jobber drill bit can deflect off center. In this example,
a small starter hole is
made using a #2
center drill bit.
The center drill bit is followed by the desired
drill bit size.
Shown is an 1/8"
stub drill bit which
has lower flex than the standard length.
The
result is a perfectly centered hole on a round part.
Note, the
DRO has a centerline finder
FUNCTION 1,
built-in.
Edge detect one side, zero the
corresponding DRO axis,
edge detect the other
side, then press FUNC 1 followed by the same
DRO axis.
When the displayed value is
set to
zero,
the cutter is centered on the part for that
axis.
Dowel-centering tool. Gauges &
DROs are
far more accurate.
Be sure to use a
center drill, first.
General Deburring Tools
Deburring tools (Israel).
The left tool has an
excellent, comfortable, durable
aluminum handle. The red-handled tool reaches
into holes to deburr
hard-to-reach (inside) holes.
Its handle has storage for extra cutters.
Deburring a
hard to access,
inside hole.
Triangular-edged, hardened
Scrape-Burr tools (Israel).
Deburring whilst the lathe turns the part.
Machinists' scrapers top to bottom: half-round,
triangular, & square-tipped
shapes (India).
A pin vise (USA), that stores needle files in the
handle, for general deburring
of machined parts.
Various types (aluminum oxide, silicon carbide,
India, Arkansas),
grits (coarse, medium, fine), &
shapes (square, round,
triangular) of stones used
for deburring, polishing, lapping, honing, etc.
Fine files (regular & diamond) of
various shapes & grits for deburring.
It is important to have good handles on
files especially when they are being used
on a part turning in a lathe as it could catch &
push it through one's hand or
worse.
A steel file card used to remove stuck
metal chips from the cutting edges.
(1) Point, (2) Cutting Edges, (3) Heel, (4) Tang, (5) File Length.
CAUTION:
Always use a handle when filing a part turning on a lathe.
If it catches, it can jam the tang into or through
your hand/eye. Wear
eye protection.
Also see the
Hand Tools Section.
Edge Deburring
Milling operations often leave very
sharp, burred edges & corners.
These edges & corners are quite sharp.
Corner Deburring
The edges have been deburred using a
fine file
at a 45
deg angle
with respect to the two
sides but the
corners are still sharp. Use a
stone if finely finished
edges are so desired.
The corners have now been lightly filed at a 45
deg angle with respect to all three sides. A part
is not completed until all sharp edges, including
holes
& corners, have been properly deburred.
Scribing,
Center Punching,
Drilling,
Countersinks,
How to
Drill the Center of
a Rod,
Edge Finder,
Drilling a Rod,
General Deburring Tools,
Edge Deburring,
Corner
Deburring
HOME