couple quick questions about tesla coil primary

im heading out of state tomorrow to a family member to get some help making my primary for tesla coil. hopefully i can get my Q's answered by morning.

question 1: i have 50 feet of .25 inch copper tubing for my primary. what is the absolute minimum spacing between windings to prevent arcing across turns? what is average or optimum? what is maximum?

question 2: my secondary is 3.5 inches outside diameter. i read that the inside of the primary should be 2 inches bigger than the secondary. does that mean the inside of the primary should be 5.5 inches diameter or does that mean 2 inches additional on each side for a total inside diameter of 7.5 inches?

hopefully i can get an answer tonite yet! thank you in advance!

Hey lokey.

The spacing between turns really isn't too critical in the sense of arcing. Since it's all one piece of wire, there really isn't much potential difference between turns, so it's not likely it will arc between them at all. .25 inches to 3/8 inches should be about right. Like I said, though, it's not too critical.

That sounds about right. 5.5" should be good for the total "diameter" of the inside of the primary. Generally you should allow 3/4 to 1 inch between the side of the secondary and the first turn of the primary. This depends on the voltage at the primary, though. You don't want it to arc between the primary and secondary. 1 inch sounds good, though.

Good luck tomorrow!
Regards,
Der Strom

thank you!!