Can anyone post some links about how to make graffiti caps for spraycans?

I've been doing graffiti for a while now, but I have always had to struggle with a very tight budget. i usually use the stock tips that come with spray cans, but i have recently branched out and bought a bunch of different types of graffiti tips to try them out. i like the effects, but the caps are all really weak and are expensive. is there any way to modify stock tips into specialty ones? Please post links to sites or supply any  ideas. thanks.

Aerospaced5 years ago
http://www.bombingscience.com/shop-tips.htm
There used to be a magazine called "Can Control"