IMPROVEMENTS IN MACHINERY FOR CUTTING DOVE- TAIL JOINTS
Year: 1866

page_text: LETTERS PATENT to Samuel Thompson Armstrong, of the City, County,
and State of New York, United States of America, now of No. 8,
Southampton Buildings, Chancery Lane, in the County of Middlesex,
for the Invention of "IMPROVEMENTS IN MACHINERY FOR CUTTING DOVE-
TAIL JOINTS." A communication from abroad by Frederick Woolcot
Armstrong, of Plainfield, New Jersey, United States of America.
-
PROVISIONAL SPECIFICATION left by the said Samuel Thompson
Armstrong at the Office of the Commissioners of Patents, with his
Petition, on the 2nd August 1866.
I, SAMUEL THOMPSON ARMSTRONG, of the City, County, and State of New
York, United States of America, now of No. 8, Southampton Buildings,
Chancery Lane, in the County of Middlesex, do hereby declare the nature
of the said Invention for "IMPROVEMENTS IN MACHINERY, FOR CUTTING DOVETAIL
JOINTS," a communication, to be as follows:-
The said Invention consists chiefly in the employment of spiral saw blades
or cutters attached to rotating cutter heads, and caused by suitable gearing
to work together in the required direction and at the required angle -to

page_text: produce the dovetail mortises and tenons in wood, metal, or other material,
which is supported upon an adjustable platform or table, and brought into
contact with the said cutters by an adjustable sliding gauge.
The blades for cutting the sides of the dovetail tenons for angle joints are
by preference attached to the cutter heads in such a manner as to project at
right angles from the peripheries thereof, while the blades for cutting the
corresponding mortises or recesses project obliquely from the cutter heads.
The amount of projection of the blade on one of the said cutter heads is
gradually increased towards its exterior or largest diameter, while the pro-
jection of the blade on the other cutter head increases gradually towards
its centre.
Although the dovetail mortises and tenons may be perfectly formed by the
use of the saws above described the operation will be greatly facilitated by the
employment of other saws secured upon the same cutter heads in such a
When these
position as to cut the bottoms of the said mortises and tenons.
additional saws are employed the substance of the wood or other material is
cut out in solid pieces instead of in the form of sawdust. The cutter heads
are firmly secured upon beveled toothed wheels geared together at such an
angle as to ensure the saw blades working properly in relation to each other.
The said toothed wheels are fitted to turn upon studs or pins, or upon short
spindles which are supported upon upright brackets firmly bolted to a strong
foundation plate, one of these brackets being, by preference, made adjustable
on the said plate to allow the proper relative position of the saw blades to be
conveniently obtained. The correct adjustment of the said blades may be
further facilitated by forming radial slots in one of the cutter heads, through
which slots the bolts for securing the said cutter head upon its wheel are
passed. The boss of one of the toothed wheels is grooved spirally, and forms
a screw whose pitch corresponds with the pitch of the spiral saws. The plat-
form or table upon which the wood or other material is placed while the
dovetails are being cut is supported by a fulcrum or centre pin passing through
a vertical slot in an upright standard or bracket. This method of supporting
the table allows the height thereof to be varied as required, and also
permits the necessary adjustment of the said table when the dovetails
are to be formed obliquely in the wood or other material, while the angle or
incline of the platform, to give the desired shape to the mortises and tenons,
is obtained by set screws or other convenient means of regulation. The
sliding gauge is guided by straight bars fitted to slide freely in corresponding
One, of these bars is pro-
grooves on the surface of the table or platform.
vided with an adjustable rod attached by a pivot or hinge to one end of the

page_text: said bar, and fitting between two lugs or projections on the other bar, beyond
which it extends to the spiral groove in the boss of the toothed wheel. This
moves the gauge a short distance along the table when the cut is being com-
menced, the motion of the said gauge being afterwards continued in the same
direction by the action of the spiral saws. When the gauge is to be moved
back upon the said platform to recommence its operation the rod is raised 'out
of the spiral groove by an elastic bar or spring, and is thereby returned to its
proper position at the end of the platform. The mortises and tenons may be
cut of any desired form and size, and may be cut for either butt joints or
angle joints of any degree, not only for ordinary cabinet and joiners' work,
but for portions of ships' planking and other work upon which dovetail joints
could not be advantageously employed if cut by hand in the usual manner.
Dovetails for mill hoppers, coffins, and other articles having similar oblique
joints can also be cut with great accuracy and economy.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Samuel Thompson, Armstrong in the Great Seal Patent
Office on the 2nd February 1867.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, SAMUEL
THOMPSON ARMSTRONG, of, the City, County, and State of New York, United
States of America, now of No. 8, Southampton Buildings, Chancery Lane, in
the County of Middlesex, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Second day of August, in the year of our Lord
One thousand eight hundred and sixty-six, in the thirtieth year of Her reign,
did, for Herself, Her heirs and successors, give and grant unto me, the said
Samuel Thompson Armstrong, Her special licence that I, the said Samuel
Thompson Armstrong, my executors, administrators, and assigns,. or such
others as I, the said Samuel Thompson Armstrong, my executors, administrators,
and assigns, should at any time agree with, and no others, from time to time
and at all times thereafter during the term therein expressed, should and
lawfully might make, use, exercise, and vend, within the United Kingdom of
Great Britain and Ireland, the Channel Islands, and Isle of Man, an Invention
for "IMPROVEMENTS IN MACHINERY FOR CUTTING DOVETAIL JOINTS," upon the
condition (amongst others) that I, the said Samuel Thompson Armstrong,
my executors or administrators, by an instrument in writing under my,
or their, or one of their hands and seals, should particularly describe

page_text: and ascertain the nature of the said Invention, and in what manner the
same was to be performed, and cause the same to be filed in the Great
Seal Patent Office within six calendar months next and immediately after
the date of the said Letters Patent.
NOW KNOW YE, that I, the said Samuel Thompson Armstrong, do hereby
declare the nature of my said Invention, and in what manner the same is to
be performed, to be particularly described and ascertained in and by the
following statement, reference being had to the accompanying Sheets of
Drawings forming a part of this Specification:-
The said Invention consists chiefly in the employment of spiral saw blades
or cutters attached to rotating cutter heads, and caused by suitable gearing
to work together in the required direction and at the required angle to pro-
duce the dovetail mortises and tenons in wood, metal, or other material,
which is supported upon an adjustable platform or table, and brought into the
required contact with the said cutters by an adjustable sliding guage.
The said Invention further consists in the employment in combination with
the said cutter heads and spiral saws of other saws which are arranged in
relation to the first named saws at the proper angle to cut the bottoms of the
dovetails. The blades for cutting the sides of the dovetail tenons for angle
joints are by preference attached to the cutter heads in such a manner as to
project at right angles from the peripheries thereof, while the blades for
cutting the corresponding mortises or recesses project obliquely from the said
cutter heads. The amount of projection of the spiral blades on the said
cutter heads is gradually increased from the point on each blade which com-
mences the cut, the greatest depth of the said blades being made to
correspond with the required depth of the dovetails. The cutter heads have
conical peripheries, and the blade on one cutter head increases in depth
to wards its largest diameter, while the depth of the blade on the other cutter
head increases gradually towards the smallest portion of the periphery of the
said head.
Although the dovetail mortises and tenons may be perfectly formed by the
two spiral saws above described the operation will be greatly facilitated by
the employment of the other saws for cutting the bottoms of the said
mortises. When these additional saws are employed the substance of the
wood or other material is cut out in solid pieces instead of in the form of
sawdust.
DESCRIPTION OF THE DRAWINGS.
Figure 1 is a plan of the top of my improved dovetailing machine fur-
nished with saws for cutting the dovetail tenons for angle joints; Figure 2 is

page_text: an end view of the same; Figure 3 is a section upon the line a, a, Figure 2;
Figure 4 shews detached portions of the said machine; Figure 5 illustrates
the arrangement of the saws for cutting the mortises; Figure 6 shews the
machine provided with the additional saw blades for cutting the bottoms of
the dovetail mortises; Figures 7, 8, 9, and 10 shew dovetails cut for various.
purposes, and illustrate the mode of forming the same. Like letters refer to
the same parts in each of the Figures.
The cutter heads A, A', are firmly secured upon beveled toothed wheels
B, B', which are geared together at such an angle as to ensure the saw
blades C, C', working properly in relation to each other. The said toothed
wheels are fitted to turn upon studs or pins D, D¹, or upon short spindles
which are supported upon upright brackets E, E', the said brackets being
firmly bolted to a strong foundation plate E³. One of these brackets is by
preference made adjustable on the said plate to allow the proper relative
position of the blades C, C', to be conveniently obtained. The correct adjust-
ment of the said blades may be further facilitated by forming radial slots a
in one of the cutter heads, through which slots the bolts 6 for securing the
said cutter head upon its wheel are passed. The boss c of one of the toothed
wheels B is grooved spirally at e, and forms a screw whose pitch corresponds
with the pitch of the spiral saws, which must be equal to the pitch or distance
between the centres of the dovetails. The projection of the saw C¹ from the
periphery of its cutter head A¹ is gradually increased towards the largest
portion of the head A', while the projection of the other saw C is greatest
at the smallest portion of the cutter head A. The platform or table F upon
which the wood or other material is placed while the dovetails are being cut
therein is supported by a fulcrum or centre pin G, which passes through a
slide G¹. This slide is secured to an upright standard or bracket H by a set
screw H', which passes through a vertical slot H formed in the said,
standard. The set screw H¹ allows the height of the table F to be varied as
required, and also permits the said table to be inclined longitudinally when
the dovetails are to be formed obliquely. The desired lateral incline of the
table F is obtained by the set screws d, or other convenient means of
regulation. The sliding gauge I is guided by straight bars J and J¹ which
are fitted to slide freely in corresponding grooves in the surface of the table
or platform F. One of these bars is provided with an adjustable rod e¹
attached by a pivot or hingef to one end of the bar J', and fitting between
two lugs or projection g on the other bar J. The rod e extends beyond the
latter to the spiral groove, e in the boss c of the toothed wheel B; this rod
when in the said groove moves the gauge I a short distance along the table

page_text: when the cut is being commenced, the motion of the said gauge and the
material being afterwards continued in the same direction by the action of
the spiral saws C, C: When the gauge I is moved back upon the said
platform to recommence its operation the rod e is guided into the spiral
groove e in the boss c by a curved elastic bar or spring K, and is thereby
returned to its proper position at the end of the platform F. The mortises
and tenons may be cut of any desired form and size, and may be cut for either
butt joints or angle joints of any degree, not only for ordinary cabinet and
joiners' work, but for portions of ships' planking and other work upon which
dovetail joints could not be advantageously employed if cut by hand in the
usual manner. Dovetails for mill hoppers, coffins, and other articles having
similar oblique joints can also be cut with great accuracy and economy.
When the machine is provided with the additional saw blades, illustrated in
Figure 6, the portions removed from the wood or other material in which
the dovetails are formed are cut out in solid pieces instead of in the condition
of sawdust. The saw blades L, L', project laterally from the blades C, C¹,
the angle at which they stand being adapted to the required form of the dove-
tails to be cut. The portion between the points a, b, on the blade C cuts one
side of the dovetails or that portion which lies between the points 1 and 2,
Figure 8, on the wood while the corresponding portion of the blade C cuts
the distance between the points 3 and 4 on the other side of the said dovetail.
When the points 6 of the blade C, C', reach the points 2 and 3 on the wood
the blades L, L', come into operation and cut out the bottoms, or that portion
which lies between the points 2 and 3. These blades L, L', should be of
such a width that the former will cut from the point 2 rather more than half
way to the point 3, and the latter the same distance from point 3 in the
opposite direction; that is, each blade should cut a little past the centre of
the mortise to ensure the removal of the portion of wood inclosed by the line
1, 2, 3, 4. If desired, only one of the cutter heads need be provided with a
saw for cutting the bottoms of the dovetails, in which case. the said saw must
be of the proper width to cut the entire distance from 2 to 3. The saw
blades are made in sections, and as each section becomes worn or filed away
it is slipped further round upon its cutter head, and a new section is inserted
behind it. The said blades are by preference filed as "rip" saws between
the points a and b, the remaining portion being filed "cross cut." This
manner of filing the saws ensures the corners of the dovetails being cut
sharply and clearly through.
The saws for cutting the dovetail mortises or recesses are shewn in
Figure 5; these saws are attached to the cutter heads in the same manner

page_text: as the saws for cutting the mortises shewn in Figures 1 and 2, but stand
obliquely instead of at right angles to the periphery of the said cutter heads.
The saw blades are all attached to the cutter heads in such a manner as to
be easily removed therefrom, and replaced when desired..
,
The required motion may be imparted to the cutter heads by means of
an intermediate shaft or pinion M, as shewn in Figures 1 and 2, or by means
of a driving belt passing over the pulleys N which are carried on the end of
the shaft of one of the said cutter heads, as in Figure 6.
The portion of
wood or other material in which the dovetail tenons are to be formed is placed
upon the platform F with one edge against the gauge I; the latter is properly
adjusted to ensure the "cut" being commenced by the saw C at the desired
point on the said piece of wood or other material; the end of the rod e¹ is
then placed in the spiral groove e, and the cutter heads are set in motion.
The saw blades C, C', in their rotation will cut obliquely through the
wood or other material in opposite directions, as more clearly illustrated in
Figure 9.
the
When the machine is first started, and the saws are just commencing to cut,
gauge I is caused to move endwise upon the platform F by the action of
the spiral groove e upon the rod e¹, which is attached to the said gauge.
This longitudinal movement of the material and the gauge I is continued by
the action of the saws C, C', which are arranged at the proper pitch and
in the proper spiral direction upon their respective cutter heads for this
purpose.
When the saws C, C', are employed without the additional saws L, L',
they must be thick enough to ensure the removal of the substance required
to be cut away, but when the latter saws are employed the saws C and C¹
may be made much thinner, as shewn in Figure 6.
Having thus fully described the said Invention as communicated to me by
my foreign correspondent, and shewn how the same may be conveniently and
advantageously carried into practice, I claim,-
First, the spiral saw blades or cutters C, C¹, constructed, arranged, and
operating substantially as and for the purpose described.
Second, the combination with the said spiral saw blades of the additional
saw blades L, L', for cutting the bottoms of the dovetails substantially in the
manner set forth.
Third, the cutter heads A, A¹, for carrying the said saw blades constructed
and arranged to operate together substantially in the manner set forth.
Fourth, the cutter heads A, A', and saw blades C, C¹, either with or with-

page_text: out the saws L, L', arranged in combination with the adjustable platform F,
substantially as and for the purpose described.
Fifth, the sliding gauge I arranged to operate in combination with the said
cutter heads, saws, and platform, by means of the rod e¹ and spiral groove e
for the purpose and substantially in the manner set forth.
In witness whereof, I, the said Samuel Thompson Armstrong, have
hereunto set my hand and seal, this First day of February, in the year
of our Lord One thousand eight hundred and sixty-seven.
Witness,
GEORGE HASELTINE,
"International Patent Office,"
8, Southampton Buildings,
London, W.C.
S. T. ARMSTRONG. (L.S.)