Stock up on dried peppers at a Mexican grocery. Go for freshest looking dried peppers. High turnover= fresh peppers. I choose a little of every variety, remember smaller peppers tend to be hotter.
Dry roast the peppers in a cast iron pan low heat rotating for 5 minutes . Cool peppers on a cookie sheet.
Use scissors to cut peppers down into 1 inch segments. Save the seeds for another operation and toss the stems.
Pulse peppers in batches. Do not overload the grinder and let the motor cool off after several rounds. Don't worry it cleans pretty easy.
CAUTION Watch your eyes! don't rub them with chili hands. Run exhaust fan while dry roasting peppers and grinding them. Once grinded to a fine consistency bag the chili powder up its ready to use.