Marking gauges are small
tools of the craft used for running outlines, and other lines on
stock, to which cutting tools are to work.
In order to produce such
lines, whether straight or curved, the edge of the stock from which
they are guided must be of the same contour, and should be perfectly
square with the surface scored. In an emergency a gauge can be made
at home by driving a brad through a stick.
Attention is directed to
Fig. 57, which gives the names of the various parts of a common
marking gauge. As will be seen, such a gauge consists of four
The bar, the head, the thumbscrew and the point.
The latter is made of steel, the other parts, of both metal and
wood, according to the maker’s idea.
The bar is usually scaled along one
side. But inasmuch as the points often get bent inward or outward,
it is best for the workman to avoid the habit of taking his sets
from this scale, and, in preference, always use his rule for them.
The head slips along the bar, and by means of the thumbscrew can be
set immovably at any point between the ends of the bar.
On the best gauges the head is faced
with inset metal to prevent wear. Where a metal thumbscrew is used
with a wooden bar, a metal shoe, to protect the bar against
dents,-should be fixed in the head at the end of the screw.
And where a metal thumbscrew is used
with a wooden head, the latter should have inset a threaded metal
bushing, to keep the threads in the head from stripping.
The point is usually a steel wire,
sharpened with a chisel-like edge, but beveled from both sides.
Ordinarily it should project about 1/4 inch at its sharp end. In cheap gauges the point is merely
held in the bar by friction of the wood; in the better gauges some
form of setscrew retains it.
Marking gauges are made for both
straight and curved work, but it is not often that they are required
for the latter purpose. It is possible to get a combination
instrument, however, wherewith, by using either side of the head,
both straight and curved lines may be made.
The ordinary curved gauge has the face
of the head concaved, and this may be used on both concave and
convex surfaces. Gauges may be purchased, too, specially constructed
for marking mortises. These tools are supplied with two points, so
that two lines may be run at one time.
As a rule, a marking gauge should not
be used on rough unplaned stock; and, in finishing work the head
must never be placed against a surface that has not been trued up.
Rough surfaced stock should be lined
with a pencil, preferably a carpenter’s pencil, with some form of
straightedge or ruler, and this also will hold good with planed
coarse, open grained woods, such as red oak and chestnut as the thin
cut of the gauge point will not show clearly on such stock.
But on smoothed close grained woods of
all kinds the marking gauge is the proper tool for lining widths and
thicknesses within its limit of reach. For bounding the other
dimension – length - the try square is used.
To set a gauge by rule, the workman
will do well to proceed as follows: Grasp the lower end of the bar
in the left hand, and the thumbscrew between the thumb and index
finger of the right hand. Hold the gauge upright, with the sharp end
of the point toward the left.
Loosen the thumbscrew, and draw the
head downward, at the same time lifting the thumb of the left hand
up along the bar until it stops the head a trifle below the
dimension desired, as shown by the scale on the bar.
Release the thumbscrew, and while the
head is supported by the thumb named, set a rule end containing the
first unit on the upper side or face of the head, so that the rule’s
dimensions will run upward past the point, touching it.
Now advance or retreat the thumb
supporting the head as required by straightening or bending it but
without moving the hand, until the desired dimension on the rule
exactly coincides with the point (Fig. 58).
the rule, and with that hand tighten the thumb screw of the head.
Test for correctness by replacing the
rule against the face of the head, holding the gauge horizontal, and
noting the dimension that comes opposite the point. The method is
shown in the accompanying illustration.
With practice, this entire operation
can be done in less than six seconds.