Classic_Boat_2016-05

COMBINATION SET

STORY AND PHOTOGRAPHS
ROBIN GATES

The combination set of square head,
centre head, protractor and rule is an
essential of the engineer’s tool chest,
adaptable to a great many uses. With
its accurately ground reference faces
it is also a favourite of the yacht joiner
and is unusual in crossing the
metalwork-woodwork divide.
This example from the 1930s was
made by Brown & Sharpe in America,
a company that made clocks before
turning to small machinists’ tools and
workshop machinery such as lathes
and milling machines. Its first
machine, made around 1850, was a
dividing engine for setting out the
graduations on a steel rule such as
the one shown here.
The rule or blade is the backbone
of the set and was available in metric
and ‘English’ (as Brown & Sharpe
termed Imperial) sizes from 6-24
inches (15-60cm). The key feature is
its clamping groove. When the rule is
inserted into the head a spring-
mounted bolt engages with the
groove and is locked in position
by a knurled nut.

The square head is the most often

used, for marking a perpendicular (for

which a scratch awl is stowed beneath

the spirit level) or acting as an accurate

depth or height gauge. Its 45^ deg

angle is excellent for marking out

mitre joints. The centre head is used

to find the centre line of round work

or, where two lines intersect, its

centre point. Using dividers, a circle

can then be scribed as a guide for

planing round timber to final diameter

• when shaping a spar, for example.
  For measuring angles, the protractor
  head is in a class of its own. The turret,
  graduated to 90^ deg either side of

zero and clamped at any angle by a

pair of thumb nuts, turns with the

precision of a Swiss watch. A built-in

spirit level is handy for establishing a

horizontal. The combination set has

been much imitated and the cheapest

die-cast alloy versions are best avoided.

Even those bearing famous names

can be suspect if manufacturing has

been farmed out.

Since machinists typically take

good care of their measuring tools,

a well-preserved vintage combination

set is usually a safe buy.

NEXT MONTH: The side axe

Clockwise from

above: Brown &

Sharpe protractor

head measuring

an angle; the

square head

used as a depth

gauge; the centre

head finds the

centre line

Traditional Tool