I take the Stackpole CB5JB20R0 which is a 5W 20 ohm resistor. I put it diagonally in my vise long ways and slightly tighten. The outer square ceramic shell cracks away and I end up with a perfectly formed smoke resistor. Much faster than cleaning the ceramic powder off the other offerings.
After a few bench tests and measuring the temperature rise in the smoke triac, I've determined that 20 ohms is the lowest you can go and still be relatively safe with the power dissipation of the smoke triac at 18 volts on the track. I've talked to people that have used one of the 16 ohm MTH resistors, but when I tested with that value at 18 volts, the smoke triac got close to 100C, too hot for me to be comfortable with it. With the 20 ohm, the triac never gets past the mid 60's in my testing. I can live with that.
