1. The cylinder diameter must not be more than 1/2 ", if its more then its becomes almost impossible to create the required pressure using hand strength.The ideal diameter is from 3/8" to 1/2".Remember more the diameter means more pressure is required.
2.Even though O rings produce good seal,to get O ring of correct size is tricky. Thats why I prefer thread gaskets.
3.Use of good char cloth is essential. It must be made up of cotton fabric and must be dry.
Step 1: You Will Need
1. Copper tube of 1/2"diameter with one end sealed by brazin 6" g to make cylinder.
2. A wooden piston to fit in the cylinder.
3. Cotton thread for making gasket.
4. Petroleum jelly as lubricant.
Step 2: Making the Cylinder
One end of the copper tube is to be sealed. I brazed a small piece of copper plate of size of penny on the end of tube tube to form the cylinder.
Step 3: Making the Piston
I used the piston that I turned using lathe machine from a wooden block. But any stick with suitable diameter may be used. It should slide in the cylinder but at the same time it must not be too loose.You can check this,while inserting it must pass through out the length of cylinder smoothly without wobbling.
The front face that goes in cylinder is drilled to hold the charcloth. And other end is turned to form grip.
Step 4: Winding the Gasket
The gasket is wound on front end of pistonby using good quality cotton thread.While winding thread must be kept very tight and adjacent turns should be pressed together using thumbnail to prevent gap.
Apply Petroleum jelly on winding to lubricate it. You need to repeat this till winding gets soaked by llubricant. This helps in providing good seal.
Now you can insert piston in cylinder. While inserting keep it turning in direction of winding. This helps in moulding of winding and provides good seal. If needed keep applying more lubricant.
Step 5: The Ember
Put some char cloth in hole drilled at front end of piston.
Place cylinder vertically on hard surface and insert piston with sharp and quick thrust. And withdraw it immediately.
If the thrust is sharp enough and if it withdrawn immediately, you will have ember.
And if you don't.....still its alright because it needs lot of practice.
I needed about fifty thrusts to get ember when I tried this for first time and now I get it in each thrust.
Please refer the following link for demonstration
This is my first instructable. Hope you find it informative and useful. Thanks
Please refer my another fire-piston, it is even easier to operate