I have had several instances of the drill bit catching and causing the whole drill chuck and arbor assembly to spin in the tailstock ram!  Not the best thing for the fit and finish of either!  I have tried to come up with some way to instal a catch for the arbor tang inside the ram, but anything I thought up or saw recommended would interfere with the tailstock screw.  I have used a wrench in the past, but trying to advance the wrench as the hole was drilled and also keep it from hitting the ways was quite difficult.  Recently I came across a simple (and obvious, once shown) solution, in a machining text.  A lathe dog!  The dog is clamped to either the drill chuck nose for smaller bits (up to about 1/2"), or directly to the bit for larger bits.  A regular Armstrong type toolbit holder is set in the lantern post with the top of the shank horizontal.  The tail of the dog is set against this and rides along the top as the bit advances.  Figure 1 shows this setup at work.

Figure 1

    In the figure I am using a 1 1/2" capacity bent tail dog.  This fits well on the nose of the Atlas chuck.  It does require, however, the compound and toolholder to be fairly close to the work.  I have now changed this to a straight tail dog, that has been further modified by grinding the body thickness down so that the clamp screw will fit into the chuck key holes.  This keeps the screw from marking the nose surface.
    I have also purchased 1", 3/4", and 1/2" capacity straight tail dogs to allow me to clamp directly to the drill bits.  I plan to use either brass shimstock or to make a brass tip for the clamp screws to prevent marking the bits.
    This, of course, works for reamers and other tools that are held by the tailstock.
 

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