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- Feb 5, 2015
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This may be an old idea but I thought of it recently. The typical grip length of an R-8 collet - the most common toolholder for small vertical mills - is about one inch. When drilling in a vertical mill, there's no need for a drill chuck arbor to be any longer than the grip of the collet. I prefer short, straight-shank arbors in a vertical mill to minimize cranking the knee up and down when changing from mill cutter to drill chuck. Take a look at the shanks of these tools compared to the modified versions at the end of this post ...
Additionally, the shank diameter should be the same as the most commonly used collets, otherwise the knee must be lowered to change collets and then raised again. Similarly, I prefer screw-machine drills to the normal "jobber's length" because of their shorter length - also because they are more rigid it's often possible to drill with screw-machine drills without first using a center or spotting drill.
Depending on the protrusion of the drawbar into the R-8 collet, a total drill chuck shank length of around 2-1/2 inches is reasonable. Given the available length and considering that only an inch or so of grip is required, a two-step arbor (1/2 and 3/4 diameters) could be practical for a manual machine. Or perhaps 3/8 and 1/2 diameters would be even better, depending on the type and size of work being done.
In either case, a stepped arbor could save the time of cranking the knee down to change collets, installing a drill chuck and then cranking it back up again. I am very happy with my reduced length drill chucks.
Too bad that I didn't think of that when I modified these:
Additionally, the shank diameter should be the same as the most commonly used collets, otherwise the knee must be lowered to change collets and then raised again. Similarly, I prefer screw-machine drills to the normal "jobber's length" because of their shorter length - also because they are more rigid it's often possible to drill with screw-machine drills without first using a center or spotting drill.
Depending on the protrusion of the drawbar into the R-8 collet, a total drill chuck shank length of around 2-1/2 inches is reasonable. Given the available length and considering that only an inch or so of grip is required, a two-step arbor (1/2 and 3/4 diameters) could be practical for a manual machine. Or perhaps 3/8 and 1/2 diameters would be even better, depending on the type and size of work being done.
In either case, a stepped arbor could save the time of cranking the knee down to change collets, installing a drill chuck and then cranking it back up again. I am very happy with my reduced length drill chucks.
Too bad that I didn't think of that when I modified these:
