Jeff et al: You raise an interesting question. Years ago, the impact of several drill sizes weighed heavier than it does today. This is because in the past, most drill machines had 8 to 10 "pods" for each spindle into which the drills were placed. When that number was exceeded, the drill operator had to manually remove and replace drills to the larger sizes, and then remember to replace the smaller drills before pressing that start button again (or face making scrap). Newer drill machines have rows of pods in which to place these drills. Operators are encouraged to touch the drill as little as possible. There are still issues with multiple drill usage: setup time is increased drills that still have good life to them are repointed or trashed prematurely if there are only a few hits used per cycle on a particular size that could have been combined with another run time can increase, with more individual drill paths to complete, and drill changes for the machine to go through The number of drill sizes is still a question asked on RFQ's (requests for quotations), so this somehow still works its way into the price you are charged for a circuit board. It is quite common for board houses to use a drill bit that is .005" over the nominal finished hole size for plated holes. It is good practice to ascertain a list of available drill sizes from your board supplier(s). Just about any size is available, but special sizes usually carry a premium from the drill supplier. As Columbo would say, "Just one more thing....": Drilling is the second-highest expense when it comes to fabbing a board (usually about 10% of the board cost). Regards, Tom Coyle Field Services Engineer HADCO Corporation *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************