This company makes dime and nickel sandpaper shapers...
(It would be nice if they made a quarter shaped shaper as well...)
http://www.excel.net/~mniver/products.html
Some cheap tip repair kits sold at Kmart, Walmart, etc. come with quarter shaped sandpaper shapers.
Do-it-yourself tip shapers...
(Electrical PVC pipe sold at home improvement stores)
Use 100 grit sandpaper (held to the inside curve of shaper with your thumb) for initially shaping your tip, then 220 grit sandpaper to re-shape tip or re-surface tip from time to time.
Cut sheets of sandpaper with scissors to size. To re-surface, hold cue vertical with butt resting on floor and lightly sand back and forth while slowly rotating cue. Once or twice around will give a nice fresh surface.
Hold shaper over tip in front of light to see if your tip needs shaping or not.
Cut electrical PVC in half and about 8 inches long - Be safe, use a vise to hold the pipe when sawing and both hands on saw.
PVC SIZES...
Dime (1/2" PVC Pipe) [15.00 mm]
Nickel / Penny (3/4" PVC Pipe) [19.75 mm]
Quarter (1" PVC Pipe) [25mm]
Half dollar (1 1/4" PVC Pipe)
Billiard ball (2" PVC Pipe)
U.S. COIN SIZES...
Dime ......................... 18.00mm
Penny ..................... 19.10mm
Nickel ....................... 21.10mm
Quarter ...................... 24.10mm
Half Dollar .................. 30.50mm