How to Drill a Hole Where You Want It
Last updated on Monday, October 14, 2019 03:11:33 PM Mountain US Time Zone


Scribing, Center Punching, Drilling, Deburring a Hole, How to Drill the Center of a Rod,
 Edge Finder, Drilling a Rod, General Deburring Tools, Edge Deburring,
Corner Deburring

Metric & Inch Equivalents
Inch to Millimeter Conversion Table
Millimeter to Inch Conversion Table
Decimal Equivalents of 8ths, 16ths, 32nds, 64ths
Decimal Equivalents of Letter Size Drills
Decimal Equivalents of Number Size Drills
American Standard Pipe Thread & Tap Drill Sizes
Tap Drill Sizes For Fractional Size Threads
Millimeter Tap Drill Sizes
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. 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.


A granite surface plate & height gauge with a carbide scribe are essential. This surface plate is
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.






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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.

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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.
Made an adjustable (brass) stop that fits into the table slot to keep parts from turning. Be sure to lock the drill press 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 & spin it & 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.

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Deburring a Hole

Chamfer, countersink, counter-bore as needed; don't leave sharp edges or corners anywhere on the
part. 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 accumulate
 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.

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KEO 53519 Cobalt Steel Single-End Countersink Set, Uncoated (Bright) Finish, 82 Degree Point Angle, 5/16" - 1" Head Diameter

Drill America DEWCHAT Series High-Speed Steel Chatterless Countersink, 6 Flute, 3/16" Shank Diameter, 3/16" Size, 100 Degrees Angle (Pack of 1)

KEO 53512 Cobalt Steel Single-End Countersink, Uncoated (Bright) Finish, 82 Degree Point Angle, Round Shank, 5/16" Shank Diameter, 1/2" Body Diameter  





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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

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 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 red-handled tool reaches into holes to deburr hard-to-reach (inside) holes.

Deburring a hard to access, inside hole.

Triangular-edged Scrape-Burr tools (Israel).

Machinists' scrapers top to bottom: half-round, triangular, & square-tipped shapes (India).

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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 on a turning lathe part.
If it catches, it can jam the tang into or through your hand. Wear eye protection.
Also see the Hand Tools Section.

Edge Deburring

Milling operations can  leave very sharp, burred edges & corners.

These edges are quite sharp as are the corners.

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, Deburring a Hole, How to Drill the Center of a Rod,
 Edge Finder, Drilling a Rod, General Deburring Tools, Edge Deburring, Corner Deburring