August 2019 37
Chuck Arbor
Getting it together
Assembly is simple but requires care. Once
the two parts are scrupulously cleaned
the arbour is “wrung” into preliminary
position by hand. This consists of simply
putting the tapered arbour in the tapered
hole and pushing them together with
a twisting motion. This seats the taper
in its hole and helps the arbour go in
straight in the final step.
Now we are ready for the application
of controlled brute force to join the two
pieces together permanently. Avoid using
excess force such as a hydraulic press,
large vice or four-pound sledgehammer.
These can drive the tapered arbour in
too far and warp the chuck body, even
jamming it. All that is needed is one or
two good blows from a medium-weight
copper-faced hammer to the end of
the arbour. Before striking such a blow,
retract the chuck jaws out of harm’s way
and set the end of the chuck on a solid flat
surface. I used a one-foot square of 5/8”
steel plate set on the end of my bench
that is reinforced around the vice. A piece
of paper was laid on it to help prevent the
chuck from skidding if my hammer blows
were not perfectly vertical, photo 5.
One firm blow from the hammer should
be enough to seat the taper. Being a belt-
and-braces kind of fellow, I gave mine
a second blow just to make sure. When
striking, avoid a pecking motion and
follow through firmly so the taper does
not try to bounce back out of its hole.
A gripping test
The first test after assembly was for
accuracy. Mounting the arbour and
chuck in the headstock spindle of The
Flagellator, a piece of round silver steel
bar was gripped in the jaws. A dial
indicator measured a runout of just one
thousandth of an inch, photo 6, a good
result indeed for a drill chuck, especially a
low-cost unit like this one.
Next came the acid test: grip under
load. A piece of scrap bar was drilled with
a 1/2” drill bit with the shank turned down
to fit the 3/8” chuck. There was no sign of
movement of the chuck or arbour, proving
there is nothing wrong with our assembly.
A final test, done mostly for amusement,
was to enlarge the hole with a 1” drill bit
fed in under heavy load, photo 7. There
was still no sign of slipping either of
the chuck on the arbour or the arbour
in the tailstock. A year of use has seen
no change in this grip under more usual
workshop conditions.Conclusion
Careful deburring and cleaning of tapers
followed by careful assembly with fi rm, but
not excessive, force creates a surprisingly
strong grip, more than suffi cient for the
home workshop. ■
A round fi le works best to deburr the end of
the chuck taper.Arbour and chuck are wrung together and placed on solid surface before the arbour is driven home.Test piece runout is measured at .001”, a
good result. Taper does not budge under load when drilling a one-inch hole with heavy feed.
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