Introduction: Knife Switch
Sometimes the project is destroyed by the choice of switch.
A simple slide switch has none of the ominous effect of a Knife Switch. An evil switch for an evil project...
The switch needs to be labeled with laser etchings for maximum effect. I could not bring myself to deface it with a simple pen
Step 1: Materials Required
I chose to use copper from old plumbing pipes and made a base from pine slats.
The screws used are brass 10-24 3/4 inch in length
Step 2: Make a Base.
I chose to make a small box from pine slats.
These are 1/4 inch in thickness and about 1.5 inches wide. They come in 48 inch lengths from HD. The length is chosen by the desired characteristics of the switch and the width is 2 pine slats wide plus to pine slat edges.
Finish the inside of all pieces before joining. This is not required but the underside will look once. Assemble and glue the pieces together and sand the outside to remove any imperfections.
The resulting box should be square and sit flat on a surface.
Step 3: Prepare the Contacts
The contact are made from Copper tubing that is standard on most home and id available from most hardware stores. A section of tube is cut to a length of about 1.5 inches than this section is cut into 4 equal strips.
For this switch I used 3/4 inch copper tubing.
The contacts were folded about a 388 inch thick piece of aluminum bar stock. The holes drilled are 3/16. The foldt are shown in the pictures.
You will need 4 contacts and 2 hinge pieces.
The 4 strips are flattened on a scrap piece of wood before the bending is accomplished.
The bent contacts have all of the burrs removed using a file and are cleaned with a green Scotchbrite pad.
The contact knives are made from a piece of 3/4 inch copper tube that is 2.5 inches long and is cut into 4 equal strips. These are flattened and cleaned as the contacts were. The ends are rounded with a file then drilled with a 3/16 inch bit at the desired pivot points.
All of these pieces are left open until later.
Step 4: Make Rivots and Backing Flanges
The rivets needed are made from 3/16 inch copper tubing. This is cut into 3/4 inch lengths than one end is flared with a tubing flare tool.
The flare tool is reversed and the flare in hammered flat on the backside of the tool creating a flat rivet face.
The backing flanges are scrap pieces of copper that are drilled with a 3/16 hole to allow for the rivet to secure to and provide a solder point to the internal switch contacts. You may want to drill som extra holes for ease of soldering later.
Step 5: Prepare the Base
Mark the base for contact points.
In this case the ends were marked and drilled with 4 contact points ( pictures show 3 but I added a forth which will be explained later.each and the face was marked with 6 points.
The points on teh face were 2 inches wide and 1.5 inches spaced apart.
The holes drilled were 3/16, the same diameter as the rivets.
Step 6: Fasten the Contacts.
Using the rivets you will need to fasten the 6 contacts to the face of the switch.
This is done bu extending a rivet through the contact, the base material, then the backing plate.
The rivets are aligned to the contacts with a scrap piece of 3/8 inch thick material clamped into a vise which acts as an anvil to the rivets. Use a piece that is wide enough to allow for 2 consecutive rivet points to be done, this will align the contact as needed.
The rivet is the staked down by flaring the tube with a punch. Hammer the punch all the way to the base and you will find that the contact is firm and secure.
Step 7: Attach the Knife
The knives are attached to the center contacts by means of a 10-24 brass bolt. This should be no more than 1/2 inch long and will be tightened enough
The handle is made from a 2 inch section of nylon rod that is drilled to accept 10/24 inch bolt. The center of the rod is cross drilled to accept a small piece of 1 inch long nylon rod as a handle.
The 1 inch rod is screwed to the the 2 inch piece and the 2 inch piece is screwed to the 2 blades of the switch.
The knife contacts are bent inward using a needle nose pliers. The contact ends should be as close together as possible. to contact the knife.
Step 8: Make Connection Points
The connection points go on the ends of the box. I made 4 input points and 4 output points.
The center 2 contacts are ground and the outer 2 connection points are power.
The power connection points are 10-24 brass screws with a nut fastened to the outside of the box. The internal wiring is soldered directly to the contact backing plates and connected to the screws. The ends of the contact wiring was looped and tinned with solder.
Brass nuts are used to connect external power.
This switch was set up with 2 independent switches.
The center or hinge point was connected to source power and the lower contact points were connected to ground.
The upper contacts were left floating and are used as a knife holder in this situation.
Remember to play safe as the contacts on the surface are live.