How to Drill a Hole Where You Want It
Also see, How to Drill a Hole in the Center of 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.
A granite surface plate & height gage with a
carbide scribe are
essential.
Surface plates are usually
±0.0001". The larger the plate, the easier it is to use.
A good height gage will easily layout scribed lines to 0.0005".
High accuracy can be achieved using
gage blocks to set the
height.
Coat the
part's surface with layout dye to make the scribe marks easier to see.
I sometimes use a precision block behind the smaller pieces.
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.
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.
I made an adjustable brass stop
that fits into the table slot to keep the piece 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.
Beware of drilling in brass; it is soft & a standard-twist
drill bit will grab the piece & spin it (and a small vise).
Lock the drill press table & clamp the work piece.
Using a mill setup with its fine
down feed is the best way to drill brass or almost anything else for that matter.
Chamfer,
countersink,
counter-bore as needed; don't leave sharp edges or corners
anywhere on the piece.
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 layout die is easily removed with 0000 steel wool and/or solvent.
Drilled holes are for clearance. The resulting hole size
is often larger than the drill bit size &
may not be perfectly round.
Precision holes are either
reamed or
bored.
Of course, a 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 & measurement/layout sections.
How to Drill the Center of a Rod
Centering a drill
hole on a rod is straightforward.
These techniques also apply to end mills and/or any other type of parts.
First, indicate the part with any
edge detector, zero the
DRO, lift the detector,
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.
Measure the part with a
micrometer or caliper.
The example rod is 0.500" diameter so the center drill 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.
Of course, these techniques extend to other part shapes.
See drill bits, how to drill a hole &
measurement sections.
See chart for bolt clearance sizes.
Also, the DRO has centerline FUNC 1.