How to Drill a Hole

How to Drill a Hole Where You Want It
Last updated on Tuesday, April 16, 2013 06:27:42 AM Eastern US Time Zone

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

Some years ago, I was making some simple, right-angle 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 to mount the Taig Mill DRO.
Wear Eye Protection Drill bits, Reamers & Counter Bores Guide for Cutting Speeds & Feeds for Drills

Scribing

A granite surface plate & height gage with a carbide scribe are essential. Surface plates are usually ą0.0001".
The larger the plate, the easier it is to use. A good height gage will easily layout scribed lines to 0.0005".
Higher accuracy can be achieved using gage blocks to set the height, if needed. Coat the part's surface with
red or blue layout dye 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.

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 punch 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.

Drilling

Next, use a sharp, #2 center drill bit because it has a small point plus it is short & therefore, stiff (having virtually no flex).
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, 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° 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.

Deburring

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 great 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.

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.

Of course, a CNC or DRO-equipped mill makes precision layout & drilling easier, but sometimes, I do not want
setup the mill for just for a few holes. These methods work well on a drill press & can be adapted for use on a mill.
Transfer punches & transfer screws are also excellent aids for aligning parts.
Also see drill bits, how to drill the center of a rod & mensuration & layout sections.
Guide for Cutting Speeds & Feeds for Drills Machinist Calculator

General Deburring Tools

Deburring tools (Israel).

Triangular-edged Scrape-Burr tools (Israel).

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.

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 ⅛" 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
appropriate DRO axis, edge detect the other side, then press FUNC 1 followed by the same DRO axis.
When the displayed value is zero, the cutter is centered on the part for that axis

Of course these techniques extend to other part shapes. See drill bits & mensuration. Chart bolt clearance sizes.

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

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