The trip wire is the trickiest assembly to make, but it isnt that difficult once you understand how it works. The trip wire is usually held in a tube that protects it from freezing - which would prevent it from working. The important thing is that the trip wire is stiff enough to perform its duties and can rotate freely in the tube. You dont want the fit in the tube too tight, a bit oversize is best because you will fill the tube with grease to prevent freeze-up. Figure 3
is a photo of trip wire and tube assembly:
I used .070 music wire that is commonly available at hobby shops. It comes in 3 lengths. You can also use 1/8 (0.125) steel rod, brazing or welding rod. You could even use a wire coat hanger by carefully straightening it.
For the tube, a common soda straw works fine, although it is a bit big and not very stiff. Hobby shops carry plastic, aluminum and brass tubing in 12 or 15 lengths. FInd a diameter that lets your trip wire freely rotate. I used plastic (styrene) tube with an inside dimension (ID) of 1/8. It came in a pack of 8 and is 15 long. Feel free to make substitutions for the tube.
The trip wire is bent at both ends as shown in Figure 4
and Figure 6
. It is important to bend the top (trip wire hook end) angled bends first since they are more complex. Once these are complete, the tube is slid in to place and the lower bends (simply two 90° bends) are made. This locks the tube in to place. The following instructions will walk you through the process.
Start with a piece of wire at least 20 long (for a 24 upright as shown here). Follow along with the steps shown in Figure 4
.Trip Wire Hook EndStep 1:
Make a 90° bend 2 from one end of the wire. Use a pair of needle nose pliers and grip the wire below the bend. Push the 2 piece that protrudes above the pliers with your thumb until you get a nice bend.Step 2
: The bend shown in Step 2
is made in order for the flag holder to clear the wooden upright when the tip-up is tripped. The short straight section before the bend must be long enough for the 45° bent section to rotate without hitting the upright. In general, the length of this straight section should be 1/2 the thickness of your upright plus a little extra (~ 1/8 is fine). (You can always cut a notch in the corner of the upright later if you make a mistake.)Step 3:
Still looking down from the top, you make a sharp bend about 1/2 from the 45° bend you made in Step 2
. This creates the straight section that the hook on the end of the flag wand catches. Grasp the wire with the tips of your needle nose pliers and bend the protruding end around them - this creates a nice little curved section that provides a little extra clearance for the flag wand.Step 4:
Finally, trim the hook end so it is about 1/2 long. You can use a fine tooth file or fine emery cloth to de-bur and polish the end of the cut wire. Figure 5
shows the completed hook end.
Figure 5Trip Wire Trip End
With the hook end of the trip wire bent to shape, you can slip the trip tube on to the wire shaft. If your tube is plastic, you might want to put a small metal washer on first, then the tube, and finally, another washer. A small washer cut from a plastic milk bottle can reduce friction on brass, copper, steel or aluminum tubes.
Follow along with the steps in Figure 6 to bend the trip end.Step 1: Figure 6, Step 1
simply shows what the trip wire will look like as you sight down from the top. It should help you understand the relationship of the trip end to the hook end - they are at 90° to each other. Once you understand this, proceed to Step 2
Grasp the trip wire right where it exits the trip tube. Make sure to leave a little clearance (1/8 or so). Make a 90° bend - making sure to align it as shown in Step 1
Make the final 90° bend 5/8 from the previous bend.Step 4:
Finally, trim the trip end so that it is 1 1/4 long. Polish and de-bur the end with a fine file or emery cloth.