AN IMPROVED MORTISING CHISEL
Year: 1879

page_text: LETTERS PATENT to Henry Stent, of Stratford, in the County of Essex, for the
Invention of "AN IMPROVED MORTISING CHISEL."
the Commissioners of Patents on the 23rd May 1879.
HENRY STENT, of Stratford, in the County of Essex. "AN IMPROVED MORTISING
CHISEL."
My Invention relates to an improved mortising chisel for carpenters', joiners',
cabinet-makers', and similar work, and which may be constructed to be placed in a
mortising machine, or to be used by hand. The said Invention is designed to
furnish a tool which while working will clear itself of the chips or debris formed in
the mortises or slots, and which will thereby obviate the inconvenience and loss of
time incurred in cleaning out the mortises when the ordinary mortising implements
are used.
My improved chisel is constructed as follows, that is to say :-Its front surface
down to its cutting edge is plain or straight across the entire width of the chisel,
but the bevelled portion immediately at the back of the cutting edge has not a
straight or continuous plane surface, but is formed with two projecting sides or
flanges which extend from the cutting edge upward to a point where they merge
into the central or channelled portion of the back of the chisel. The cutting edge
therefore consists of two narrow projecting portions on these flanges, and a central
wide portion between them. These flanges are made taper from the point upward
in such a manner that the central space or channel between them is narrower at
the cutting edge or at a point slightly above the same than at any other portion of
the chisel.
The result of this improved formation of the said chisel is that each chip or

page_text: shaving cut thereby in making a mortise or slot in a joist or other piece of wood,
instead of being left in the mortise as the chisel rises, will be cut clear of the sides
of the mortise at the bottom of the same by the cutting edges of the said projec-
tions, and will be caught and held between the said projections, and in the next
descent of the chisel will be pushed upward out of the same, and left outside of the
mortise.
Consequently there will be no accumulation of chips or shavings in the mortise
as the work proceeds, and no delay incurred by stopping to clear out the mortise or
hole, and I entirely obviate the danger of splitting off the sides of the mortises,
which frequently happens with light work in the use of implements for cleaning
out the debris from the same.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Henry Stent in the Great Seal Patent Office on the 22nd November
1879.
HENRY STENT, of Stratford, in the County of Essex. "AN IMPROVED MORTISING
CHISEL."
My Invention relates to an improved mortising chisel for carpenters', joiners',
cabinet makers', and similar work, which chisel may be constructed to be placed in
a mortising machine, or to be used by hand. The said Invention. is designed to
furnish a tool which while working will clear itself and the mortise or slot of the
chips or debris formed in the same, and which will thereby obviate the inconvenience
and loss of time incurred in clearing out the mortise when the ordinary mortising
implements are used.
The said Invention is illustrated in the accompanying Drawing, in which,―
Figure 1 is a front view of my improved mortising chisel.
Figure 2 is a longitudinal section on the line x, x, Figure 1.
Figure 3 is a back view of the same, shewing the said chisel formed with a shank
to fit the socket of a mortising machine.
Figure 4 is a transverse section on the line y, y, Figure 3.
Figure 5 is a longitudinal section of my improved chisel, shewing the same adapted
for hand work.
Figure 6 is a back view of a large chisel.
Figures 7 and 8 are back and side views of a small chisel.
Like letters indicate the same parts throughout the Drawing.
My improved chisel is constructed as follows, that is to say:-Its front surface
down to its cutting edge a is plain or straight across the entire width of the chisel,
while the bevelled portion immediately at the back of the cutting edge is formed
with two projecting sides or flanges b, which extend from the cutting edge a upward
till they merge, as shewn at c, into the main portion of the back of the chisel. The
cutting edge therefore consists of two narrow projecting portions b', and a central
wide portion between them, as clearly shewn in Figure 1. The flanges b should be
made parallel from the cutting edge a upward to about the line e, and taper from
this line e upward in such a manner that the central space or channel & between the
said flanges is narrower in the part from the cutting edge as far as the part e than
at any other portion of the chisel.
This formation of the central groove or space, so that the sides of the same are
parallel for a short distance from the cutting edge, and taper above this parallel
portion, is a very important feature in the construction of my improved chisel. The
parallel portion holds the chips with sufficient tightness to ensure their coming with
it from the mortise or slot as the chisel rises therefrom, while the divergence or
tapering of the sides above this parallel portion permits the release and discharge
of the chips as the chisel descends into the mortise after rising from the same.
It will be obvious that I use the term parallel in the ordinary sense in which it
is used in mechanics, and that I do not intend to restrict myself to a mathematical
or exact parallelism of the parts of the chisel above described as the purpose of this
construction, that is to say, the holding of the chip to bring the same out of the
mortise, may be effected with more or less certainty when the said parts of the
chisel are approximately parallel, or so nearly parallel that their divergence is not
perceptible without very exact measurement. This peculiarity exists in chisels of
all sizes, from the smallest to the largest constructed according to my Invention, but
is more perceptible in large chisels, as will be seen by reference to Figure 6.
It will be seen by reference to Figures 2 and 4 that the greatest depth of the
flanges b is at the angle e¹, formed by the convergence of the back and under surfaces
of the flanges b. By giving this great depth to the flanges just above the cutting
edge, and at the narrow part of the channel d, I further provide for ensuring the

page_text: holding and bringing out of the chips or shavings from the mortise by the chisel,
and their release from the same, as above described.
In machine-mortising chisels the part at fis usually left very thick to afford the
required strength, but it will be seen by reference to Figure 2 that while giving to
the chisel the required thickness I make this part of the said chisel nearly flat, that
is to say, the surface of the channel or central space d from the edge a to the part c
is nearly straight; and in hand chisels, in which less strength is required, it is
preferably quite straight, as shewn in Figure 5. This flatness of the back of the
chisel at the part prevents the pushing out or disengagement of the chip
or shaving from the flanges b by this part before the chisel rises out of the
mortise.
The proportion of the width and thickness of my improved chisels varies according
to the sizes of the same; for instance, in small chisels, such as are shewn in Figures 7
and 8, the thickness of the chisel is greater than the width to give the required
strength and stiffness to the chisel, but in the larger sizes of chisels this proportion
of the thickness to the width is considerably diminished, as shewn in Figures 1,
2, and 3.
'
The result of my improved formation or construction of mortising chisels is, that
each chip or shaving cut thereby in making a mortise or slot in a joist or other
piece of wood, instead of being left in the mortise as the chisel rises, will be cut clear
of the sides of the mortise at the bottom of the same by the cutting edges of the
said projections b, and will be caught and held between the said flanges or projec-
tions at and below the part e, and at the commencement of the next descent of the
chiscl will be pushed upward out of the same, and left outside of the mortise ;
therefore there will be no accumulation of chips or shavings in the mortise as the
work proceeds, and no delay incurred by stopping to clear out the mortise or hole,
and I entirely obviate the danger of splitting off the sides of the mortises, which
frequently happens with light work in the use of implements for clearing out the
debris from the same, and these chisels can be adapted to any existing mortising
machine.
Having thus fully described my said Invention, and the manner of performing
the same, I wish it understood that I am aware of other chisels having been made
with flanges or projections at the sides; I therefore do not claim broadly or other-
wise than in connection with the peculiar features above described a chisel with
such flanges or projections, but I claim,―
A mortising chisel with flanges or sides whose extremities project and form the
exterior portions of its cutting edge, which flanges are so formed that the channel
or space between them has its greatest depth and parallel sides from the cutting
edge for a short distance above the same, and from this parallel portion upward
the said sides are tapered, all as shewn and described, and for the purposes
specified.
In witness whereof, I, the said Henry Stent, have hereunto set my hand
and seal, this Twenty second day of November, in the year of our Lord One
thousand eight hundred and seventy nine