January 1942 ET-189
United States Department of Agriculture
Bureau of Entomology and Plant Quarantine
A LEAF PUNCH FOR USE IN INSECTICIDAL RESIDUE STUDIES
By Robert A. Fulton, Division of Insecticide Investigations
There is often need for a sampling device to remove portions
of a leaf of kno-,n area for the determination of dust or spray
residues. The leaf cutter herein described vwas constructed to
provide a unit to remove 2 square centimeters of leaf material
from a citrus leaf.
The essential principle involved is similar to that commonly
used in leather punches, i. e., the cutting unit is forced through
the material against a soft surface, such as lead or tin. This
principle is n:ore satisfactory than the shearing action used in
cardboard and paper punches.
The unit was designed to be operated by one hand and with
an action and a grip similar to those used in small firearms. By
increasing the length of the trigger all the fingers are used
in applying the pressure to the cutting head. The upper end of
the trigger is designed to produce a maximum travel of the thrust
arm while the cutter is being closed. The curvature of the trigger
arm is such that a compound lever effect is obtained near the end
of the stroke. The leaf is then forced against the cutter by
the lead disc on the end of the thrust arm. The leaf disc remains
in the cutter and is gradually forced into a test tube, which
holds the sample. When all the discs have been cut from the
respective plot, the remaining discs are forced into the test tube.
A small counter is mounted on' the side of the sampler with a
connection to the thrust arm.
Two views of the apparatus are shown in figures 1 and 2
and a sectional drawing in figure 3.
Tn the construction of the punch, the frame, trigger and
thrust arm (A, B, C, fig. 3) were cut from quarter-inch sheet
aluminum. Ti)e trigger was maeie in three pieces and riveted together
to provide a bearing on both sides of the frame. The compression
unit (D) was made of brass. A slot was cut to allow the unit to
straddle the frame and form a double bearing at K. The top of the
compression unit was threaded for a flanged cap to hold a lead
disc. The cutter holder (L) was made of brass and grooved to fit
over the frame. This unit was then held rigid by rivets. The
test tube holder (G) was made to fit over the end of the frame.
A small steel wire loop covered with rubber tubing was used to
support the glass tube. Holes were drilled in the removable unit,
and the wire support was attached with solder. The support was
then drilled and threaded for a screw (H) to hold the test tube
holder in place. A sponge rubber gasket (F) was inserted between
the end of the test tube and the cutter holder to prevent breakage
of the glass when the punch was being used. The cutting unit (E)
was machined from five-eighths-inch steel tubing. The cutting tool
was tempered in powdered sodium cyanide. This process will produce
an exceptionally hard cutting edge. A small spring (J) was used
to release the punch.
The device has been used for 1 year in determining the
sulfur deposits on orange and lemon foliage. The unit has operated
with entire satisfaction. It has been found necessary to replace
the lead plate after cutting approximately one thousand discs.
Figure l.--General view of leaf punch.
Figure 2.--Photograph of dismantled leaf punch, showing
construction of test tube holder and lead disc cap.
Figure 3.-A drawing of the leaf punch, showing arrangement of integral
parts. A, Aluminum frame; B, trigger arm; C, thrust arm; D, compres-
sion unit; E, cutting tool; F, sponge rubber; G, test tube support;
H, screw to fasten support to the punch; I, test tube; J, spring to
release punch; K, bearing for compression unit; L, cutting tool
holder. This drawing is approximately one-half natural size.
UNIVERSITY OF FLORIDA
II3 1262 09240 962111
31262 09240 9621