Can i make my own power tool charger for a obsolete cordless drill?

If the charger is not readily available, the option is only to make one. Most old drills had 12V NiCd type batteries. One easy solution is to take a Mains - 14 or 15 V transformer of 1A, a bridge rectifier and a 1000uF capacitor to generate a basic 12V DC supply. This may be regulated using a 7812 regulator to get good 12V. There are numerous circuits of this type, which you can search for, but this is the basic scheme. Ideally you should have a constant current charger charging at 1/10 the AH rating of the battery, but then the circuit would be complex.For more info on cordless drills http://www.cordlessdrillsinfo.net/