AW Extra 5/24/12 – Super-Tune Your Tools with a Dial Indicator

What is a dial indicator?

A dial indicator is nothing more than a spring-loaded rod, a needle and a dial. Move the rod up or down and the needle rotates around the dial's face. The dial tells you how many thousandths of an inch the rod has traveled. The one at right is measuring the thickness of a dollar bill at .003 in.

A complete dial indicator kit also contains a magnetic base, a long articulating arm and a set of contact points.

The heavy magnetic base holds the instrument absolutely rigid on any metal surface. It's not electronic (there's no cord to plug in); you flick a switch to raise or lower the magnet inside the base.

The articulating arm is used for holding the dial at a distance from the base. It's tricky to adjust, so we won't use it for these two jobs.

Contact points screw onto the bottom of the measuring rod. Each one has a special shape for measuring different kinds of objects. We'll be using three contact points: a ball, a disc and a bent arm.

Zero the dial

The first step in using a dial indicator is to turn the dial so the zero mark lines up with the needle. This way, you don't have to add or subtract any numbers to calculate how far the needle moves when measuring a distance.

Let's practice on the top of the tablesaw. Install a disc contact point on the end of the rod and place the base on the saw. Turn on the magnet. Clamp the dial and rod so the contact point touches the table and slightly compresses the spring-loaded rod. Turn the dial to zero and you're ready to go.

Click any image to view a larger version.

1. Turn off the magnet. Clamp the base to the miter gauge so the rod is slightly compressed when it touches the saw blade just below a tooth. Mark where the contact point touches the blade. Zero the dial. Caution: Unplug your saw for these procedures.

2. Measure the back. Rotate the blade by hand and realign the marked spot with the contact point. If the needle has moved less than .003 in. either way, you're OK. If it has moved more than .003 in., the saw's trunnions or table should be adjusted. Consult your owner's manual for step-by-step help on aligning the blade.

3. Measure the front of the fence. Reposition and clamp the dial indicator on the right side of the miter gauge. Slide the fence so it slightly compresses the rod. Lock down the fence. Zero the dial.

4. Measure the back. Slide the dial indicator to the back of the fence and check the reading. If the needle is off the zero mark, adjust the angle of the fence until you get the same reading front and back. Consult your owner's manual about how to make this adjustment.

1. Zero the dial. Install the bent-arm contact point on the dial indicator. Place the dial indicator on the infeed table and turn on the magnet. Clamp the dial on the base's post so the spring-loaded rod is slightly compressed. Turn the dial to zero.

3. Level the outfeed table. Reposition the dial indicator so the bent arm touches the outfeed table. (On some jointers, you may need to use the articulating arm to reach across the tables.) Raise or lower the outfeed table until the needle reads zero. Lock the table.

5. Change contact points. Remove the bent-arm point and install the disc. The wide, flat bottom of the disc makes it the best choice for knife-setting. The disc gives you more latitude in positioning the dial indicator on the table when the knives are at top dead center. Zero the dial again.

7. Zero the right side. Rock the knife by hand back
and forth through top dead center. If the needle
never reaches zero, the knife is too low. If the
needle goes above zero, the knife is too high. If you
used a knife-setting gauge, readjust the height of the
outfeed table until the needle reads zero, and leave the
table there for all three knives. Otherwise, adjust the
height of the knife until the needle reads zero.

2. Zero the infeed table. Raise or lower the infeed table until the depth-of-cut scale reads zero. If you haven't reset this scale in the past, this step ensures that your knives will project the correct distance from the cutterhead. If you have reset this scale, consult your owner's manual about how far the knives should project above the cutterhead.

4. Mark the top dead center. This is the position of the cutterhead where the knives reach their highest point. Apply a piece of masking tape to the fence and place a ruler across the tables. Turn the cutterhead by hand. Mark the spot where the knives touch the ruler.

6. Position the dial indicator. Slide the fence out of the
way. Remove all the dull knives from the cutterhead
and install sharp ones. Use the knife-setting gauge
if you have one. Snug the knives and slide the fence over
the end of the cutterhead. Place the dial indicator’s rod in
line with the top-dead-center mark and directly over the
jack screw under the knife.

8. Level the knife. Move the dial indicator to the
left side of the knife, directly over the jack screw.
Sight down the rod so it’s still in line with the topdead-
center mark. Rotate the knife again and watch the
needle. The reading on this side of the blade should
be within .002" of the reading on the other side of
the blade. Raise or lower the left side of the knife as
needed. Recheck the right side and tighten the knife.
Repeat Steps 6 through 8 for each knife, zeroing each
to the outfeed table.

If the edge is concave, use your dial indicator to
lower the outfeed table in .001" increments, as
shown in Step 3. Keep adjusting until you can
joint a straight edge.

Two other problems also indicate an outfeed
table that’s too high. 1. The board bumps into the
leading edge of the table. 2. The cut always trails
off to nothing as you joint an edge.

Snipe at the trailing end of the board tells you to raise the outfeed table. The snipe shown above is quite large, but sometimes it's so small you can only feel it. Raise the table in .001-in. increments until you can't see, feel or hear any snipe.

Source

(Note: Product availability and costs are subject to change since original publication date.)

Little Machine Shop, littlemachineshop.com, 800-981-9663, Dial Indicator, Magnetic Base and Point Set, #1782.

This story originally appeared in American Woodworker January 2005, issue #112.

January 2005, issue #112

Purchase this back issue.