I will attempt to explain how I go about designing a sliplock folder. I
decided to use a three-blade as example, that way the you can see the basics
used to design a trapper, single blade and up to a five blade.
The tools you will need: Some design references, tracing
paper or architect's film, clutch pencils, compasses
If you struggle with curves and drawing clean lines, a set
of "French curves" might come in handy.
Decide on the size of your knife's handle. Use your palm or
fingers to measure from, a large folder might be five finger widths long, a
medium folder as long as a hand width, and a small folder about three finger
widths.
Draw two vertical lines show the length of your folder when closed.
Draw two horizontal lines to give an indication of the width.
Draw the shape of your handle within this box.
Place a sheet of tracing paper over your handle design and
trace the outlines of the handle.
Draw the spring and draw light lines at each end, slightly above halfway
between the spring and the bottom of the handle.
Adjust your compass to draw a circle as shown. Note that the
circle extends over the bottom of the spring. This is how much the tang of the
blade will push up the spring when the blade is being opened or closed. The
bottom and side of the circle must be within the outlines of the handle.
The centre of these circles will be the centre of your knife's pivot pins.
Use your compass and draw three arcs:
One for the main blade, and two for the smaller blades.
Draw the three blades, the tips on the arcs.
Trace the main blade and its companion on a piece of tracing
paper. Using the tip of your compass, swing the tracing over the main drawing.
You must now check that the tips of the blades are inside the handle without
the edge touching the spring.
If the edge touches the spring and the tip is outside, redraw the blade.
Trace the bottom of the spring onto the top sheet
Swing the top sheet into the open position and draw the
front and back kicks (where the blade will rest on the spring when the knife
is closed) using the tracing of the spring bottom as guide.
Repeat these steps for the blade on the other end
Make sure there will be enough room for a nail nick!
Check and re-check that the blades will fit as they are supposed when the
knife is opened and when it is closed. Correct your drawings as necessary. On
the picture above you can see where I have made some corrections. (I sometimes
have to do a design three times before everything works as it should.)
The last step is to place the loose blade tracings underneath the sheet with
the full knife, draw the detail of the blades. and add the spring for the main
blade.
The completed design, ready for photocopying. Five copies
for sticking onto sheet metal to make the templates, and one for filing.
