Model Engineers’ Workshop – August 2019

36 http://www.model-engineer.co.uk Model Engineers’ Workshop

Mounting a drill chuck

on a tapered arbour

A

new drill chuck and Morse taper
arbour purchased recently arrived on
my doorstep in two pieces, photo 1,
But not to worry. Assembly is a simple matter
using the most basic of tools, photo 2, and
the job has since proved both accurate and
surprisingly sturdy.
Two diff erent tapers make up the typical
drill chuck arbour. The longer end is a Morse
taper that must fi t into your lathe tailstock
or drill press spindle. In the case of The
Flagellator, my 1937 Drummond M-type
lathe, this is a smallish No. 1 Morse taper.
Later Myfords and Far Eastern mini-lathes
will take the larger No.2 Morse taper here.
The arbour’s other, shorter, taper is usually
a Jacobs taper, designated in this case a JT2.
Or it might be a more modern DIN standard
taper designated as a B12 or such. In any case,
it must be the same taper as the hole in the
chuck body. Oft en this is marked on the body,
and usually on the packaging it comes in.

Initial clean up
As both chuck and arbour were low-cost
hobby market items, careful inspection
revealed some burrs left at the ends of
both male (arbour), and female (chuck),
tapers. These burrs need to be removed
before assembly or they will stop the tapers
from gripping each other. The arbour was
supplied hardened so small diamond fi les
were used, a fl at one for the arbour, photo
3 , and round for the chuck, photo 4.
Cleanliness is next to godliness if you

want a heavenly bond between tapers.

They depend on the wedging action of

the tapered surfaces to stick together

and transfer the rotational load when

drilling. Any trapped particles will keep

the surfaces separate and deter gripping,

so acetone was used to wash away any

fi lings and grease or dirt on the male and

female tapers. It is best not to use alcohol

or degreaser as these can leave salts or oils

on the tapers which impede grip. Harley-

Davidson race team engineers for many

years washed their tapered crank pins

with distilled water before assembly for

this reason. With 80 to 100 horsepower

going through a single crank pin, grip was

critical. Whichever fl uid you use, fi nal clean

is a wipe down with a lint-free kitchen

wipe or cloth. Once cleaned, do not leave

fi ngerprints on the mating surfaces.

Pete Barker strikingly demonstrates the power of tapers carefully

assembled with basic tools

1

Chuck and arbour arrive in two pieces, ready to be assembled. Assembly tools are a copper faced hammer and diamond fi le.

Great care must be taken to remove burrs from the taper ends.

2

3