How can I make my own potentiometer?
MAKING YOUR OWN VARIABLE RESISTORS

Anything conductive, accessible, doesn't oxidise, able to be "wiped" with a wiper (resistor pickup) with adequate dying "too quickly".

As this is as much for fun as anything else "too quickly" may be able to be of lower duration in time or cycles than usually.

Resistance values that you generate may be lower than not, depending on material used.

Properly "potentiometer"  mans a 3 terminal device with voltage across it and a sliding voltage tap but I'll take it to also just mean 'variable resistor.

Connection to start may be with "crocodile clips or pushed in "drawing pins" / "thumbtacks/other.


Pencil lead.   

Select an old (or new) pencil.
Sharpen both ends.
Measure resistance to see what sort of pot resistance you are going to get.
CAREFULLY break open and remove the lead intact.
May need a few pencils to get it right.
Connect clips at either end.
Connect ohmmeter to one end.
Run other ohm-meter along length and note variation in resistance.  

If you connect a voltage across length then you can use a slider to puck off variable voltage with position.
Resistance wire

In place of the pencil lead above you can us a length of new or used resistance wire.
Wire can be strethed tight between eg thumbtacks or nail in a piece of wood.
Note that wood becones part of the resistor.
New Nichome or Chomel wire canbe bought for modest cost.
Ohms per metre varies with thickness - thinnest possible is liable to be best.
Around 10 ohms/meter is common but higher R is possible.

Nichrome from old heater or toaster element works.
This may be somewhat oxidised with age and may be brittle.
You can sand surface carefully once stretched in place.
Butyl Rubber and friends

Black rubber used for roofing has carbon black in it.
Take meter and wander round sticking probes in rubber on sale and other material.
When you find a sheet of substance that has some resistance acquire a small sample by best permissible means and cut strips to make a pot.
Paper and salt water.

Lay out a strip of newspaper
Wet well but not until soggy with salt in water solution.
Test pot.
Note how result varies with salt concentration, degree of saturation of paper, passage of time, ...

Try copper-sulphate in place of salt.
Try "Epsom Salts"
Try ... ?
Copper wire

!!!
(1) Get thinnest possible bare copper wire.
Measure resistance.
Low but usable.

(2) Now for a very good trick.      

Get thinnest (within reason) enamel or varnish or polyurethane insulated copper wire. Sortthat insulation can be "sanded" off with care.
Find a "former" that is an insulator and that you can wind your copper wire on.
Round or oval cross section is good.
Once you have built one you will get a better feel for shape that is needed. 
Wind copper carefully and neatly in a long ish coil along formr. Many turns.
Not too too many the first time.   

Wind neatly so turns stack against each other neatly.
Fasten carefully at both ends.
Now CAREFULLY use fine sand paper to sand along top surcae of coil so you expose copper on each turn BUT DO NOT TAKE OFF SO MUCH THAT COIL TURNS ALL GET SHORTED TOGETHER.   

Run a wiper along the bared copper.
You have a wire-wound variable resistor.
"Plastic"

Use epoxy resin and silicone rubber.
Fill with various amounts of carbon black, or pencil graphite or powdered metal etc.
Make a track.
Let set.
Test.

Also silver filled compound used for PCB track repair.

Also ??? - look around you ... . 


By now you should have a few other ideas.

Report back :-) !!!!