Step 6: The main piston
When the glue is hardened, press it out from the cylinder (use the wooden staff). Use a hammer and hit the wood carefully. It's not so easy, but it works.
Now cut the uneven Part of the piston with a saw. Smooth down the piston and the cylinder very well. Smooth down the piston so long, until it moves very easy in the cylinder.
It is very important that the piston easily moves in the cylinder and seals this, nevertheless, very well.
Drill a 1 mm hole across the bottom side of the piston. Attach a 0.8 mm wire with two isolation parts (for centering). Don't forget the piston rod. This is made of 0.8 mm wire. At the ends make a very small loop with the round nose pliers. The length over all is 60mm.