Scavenging one from an old radio was not an option. Since most of new radios uses analog tuning. And the ones with air variable capacitors are very rare, and are collectors item.
I have read an article once about building an air variable capacitor. So i decided to build my own from scraps of aluminum sheets and from things that are easily found around the house.
If you have a drill, a scissors, a file and some sandpaper. You can easily build this one. It doesn't require much skills.:-)
I made mine from aluminum sheets 1.5 and 2mm thick. The housing is from an aluminum heatsink, i also manage to get 3 pieces of bolts with a few nuts from my junk box. The plastic bushing which also acts as an insulator is from a plastic pen and some plastic jar caps.
I also made my own washers/spacers from the 2mm thick aluminum sheet.
The contacts of the rotor which also acts as a tensioner. Were from a broken washingmachine timer.
You can experiment with the number of plates and with the size op gaps by adding more plates and washer, in the rotor and stator.
Step 1: Marking the Center for Pilot Holes
Lay the aluminum sheet flat on your work bench. From on end draw a square measuring 5cm x 5cm. Using a sharp object like a nail or file.
Get the center and punch a hole in it using a small nail. Punch a hole for every 5 centimeters along the straight line as shown on the photo.
Step 2: Draw Some Circles
If you dont have a compass.You can improvise, by driving two small nails on a small piece of wood.
Insert one nail on the hole that you made on the sheet and turn it. It is important that the circles doesn't overlap. So that we will have enough space when we cut them out later.
You can make as many circles as you like, if you have enough aluminum sheet. It is better to have a spare you if you made a wrong cut. Than to repeat the same process if we you ran out of pieces at the middle of your project.
Step 3: Marking Lines for the Stator Plates
It is important to do this, because we need each part to be uniform in size. And this also serves as a guide when we cut them out.
Step 4: Cutting
You can also use a hammer. But be very gentle.
Step 5: Marking the Holes for the Stator
Get the centerline (from corner to arc) and punch a hole in it.
Mark this piece as pattern.
Put it on top of another piece. And puch a hole on the second piece under it. Using the hole on the first piece as a template. Flip the pattern and punch the second hole.
We do this because we will drill all the rotor and stator plates one at a time. I dont recommend stacking all the pieces and drill them all at one time. The drill bit always tend to bend. Or you may if you have a drill press
Step 6: Marking the Inner Circle
Using a scissors cut it from both end, up to the arc of the inner circle. Be very carefull not to cut it all the way to the center. :-)
when all of the pieces are cut. Flatten them again with a rubber mallet.
Step 7: Cutting the Arc
But it's easier and faster if you use a curved chisel. (the one's that wood carvers use)
I have one but i don't want to ruin it.:-)
So i made one from a small pipe. Sharpen it at one end with a file. And removed half of it. So that it will be just like a curved chisel.
Dont get confused when cutting. The rotor must have the part with a hole in it. (This is where the spare pieces come in handy:-)
Step 8: Drilling
Step 9: Turning With a Drill
Stack all of the rotor plates facing each other forming a circle. (we do this to avoid vibrations when we turn them with a drill) Insert the bolt and tighten the nut.
Insert the end of the bolt on the chuck of the drill. Just like a normal drill bit. Turn on the drill and use the file to smoothen the sides of the rotor plates. Be very carefull set the drill at low speed. Do not press the drill swith for a long time. (the nut may loosen) if this happens reverse the direction of the drill.
Finish with a fine sand paper
Step 10: Shaping the Stator Plates
Like what we did with our rotor plates. We will also stack all of the stator plates. Insert the bolts on each hole, and tighten the nuts. If you have a bench vise so much the better.
If you can see the photo clearly. I colored the parts to be remove with a black pen. Or just simply follow the arc and avoid the head of the bolt and the nut. Be patient you can do this with a coarse file. Remember aluminum is not that hard to work with. :-)
Step 11: From This to That
At this point you can also remove the paint. If they have paint on. And check again for curves or if ever they are crooked.
Step 12: Making Your Own Washers
Cut a strip of aluminum about 1cm. wide. Drill holes in it using the same drill bit you used for the stator and rotor plates. Cut the strip into squares. Making sure that the hole you drilled is on the center. Insert the bolt with its head on top. Then cut the corners using the head of the bolt as a guide, as seen on the photo.
Step 13: Finishing Your Washers
Step 14: Rotor and Stator Assembly
Step 15: The Housing
I placed the rotor and stator on top of it. leaving a distance of 1mm. Between the rotor and stator. Marked the 3 holes to be drilled using the rotor and stator holes as template. Then drilled all the holes using the same drill bit used for the rotor and stator plate. Then i just cut it in a triangular shape and rounded all of the corners.
Step 16: The Insulator
Step 17: Plastic Jar Caps
Now you just put the two triangular plastic on both sides. Followed by the two triangular shaped aluminum and you are done.
Remember if you have two stator plates, you must have three rotor plates. 4/5, 5/6 and so on.
I hope that this instructable will be of much help. Thanks :-)