11-27-2015, 10:03 AM
I believe there is an underlying issue as many machinists expect a vertical mill with a DRO to be as accurate as a jig borer. Let's face it that's just not going to happen. Center drilling, drilling & reaming a hole on a mill will fairly accurately locate a hole, but it's not going to be within .0002" or so like with a jig borer. Larger holes can be bored which will improve the accuracy of the location, but will still not be of jig borer accuracy, unless one spends an insane amount of time and utilizes indicators with .0001" or tighter accuracy for the adjustments.
If you have parts that absolutely have to have very accurate hole locations one of the best ways to insure the accuracy is to drill & ream the holes with the parts assembled.
I've never expected a drill chuck to have an accuracy of .002" or less, in reality they typically have .005" or more run out like a 3 jaw chuck. Common wear & tear, spinning a drill bit, dropping it, and other issues reduce the accuracy of a drill chuck. Even more so when the chuck is used in a shop with multiple personnel.
If you have parts that absolutely have to have very accurate hole locations one of the best ways to insure the accuracy is to drill & ream the holes with the parts assembled.
I've never expected a drill chuck to have an accuracy of .002" or less, in reality they typically have .005" or more run out like a 3 jaw chuck. Common wear & tear, spinning a drill bit, dropping it, and other issues reduce the accuracy of a drill chuck. Even more so when the chuck is used in a shop with multiple personnel.