a-Knot Trick [167]

Tie a double knot in a silk handkerchief, as shown in the
accompanying sketch and tighten the last tie a little by slightly
drawing the two upper ends; then continue to tighten much more,
pulling vigorously at the first corner of the handkerchief, and as
this end belongs to the same corner it cannot be pulled much
without loosening the twisted line of the knot to become a
straight line. The other corner forms a slip knot on the end,
which can be drawn out without disturbing the form, or apparent
security of the knot, at the moment when you cover the knot with
the unused part of the handkerchief. When the trick is to be
performed, tie two or three very hard knots that are tightly drawn
and show your audience that they are not easy to untie. The slip
knot as described then must be made in apparently the same way

[Illustration: Knot Trick]

and untied with the thumb while the knot is in the folds of the
handkerchief.

** Gear-Cutting Attachment for Small Lathes [167]

When in need of small gears for experimental or model machines the
amateur usually purchases them, never thinking that he could make
them on his own lathe. A small attachment can be made to fasten in
the tool post of a lathe and the attachment made to take a mandrel
on which to place the blank for cutting a gear. The frame is made
from a 1/2 in. square iron bent as shown in the sketch with the

[Illustration: Gear-Cutting Attachment for Lathes]

projecting end filed to fit the tool post of the lathe. A pair of
centers are fitted, one of which should have a screw thread and
lock nut for adjustment in putting in and removing the mandrel.

All the old clock wheels that can be found should be saved and
used for index wheels. All of these wheels should be fitted to one
end of the mandrel. The blank wheel is put on the outer end of the
mandrel and a clock wheel having the number of teeth desired
placed on the other end. When the mandrel is put in between the
centers a small pawl is fastened with a screw to the frame with
its upper end engaging in a tooth of the clock wheel. One clock
wheel will index more than one number of teeth on a blank wheel.
For instance: if the clock wheel has 18 teeth it can be made to
index 6, 9 or 18 teeth to the blank by moving the number of teeth
each time 3, 2 and 1 respectively. In the sketch, A shows the end
of the cutter and B the side and the shape of the cutting tool.
When the cutter A, which is