Improving the mini lathe tailstock

The first time I tried using my mini-lathe's tailstock I realized it needed help.  The drill bits were far from the center of the work-- so much so that I broke the tip of my center drill when I tried to start a hole!

I sort-of addressed the problem by making a toolpost mount for a drill chuck -- but it requires alignment every time I use it.  Plus, the forces tended to lift the carriage.  So there still were reasons to work on the tailstock.

The first thing to do was to get the top of the base parallel to the lathe bed, and the vertical boss exactly perpendicular to the bed.  I began by measuring the variation in height from the front to the back of the base.  I found the back was higher by .010".  This measurement would come in handy later on in the machining procedure.

Since the "vee" in the base establishes the alignment of the base relative to the bed, I arranged things so I could align the base with respect to the vee.  I did this with a precision-ground linear rod -- see below:

The DTI is a .0001, and I was able to align the rod/base to within about .0002".  If you look closely, you can see that the right side of the base has already been milled.  The photo shows the base being set up to mill the left side.  Also, before rotating the base to mill the ends, I milled the boss (the vertical "fin" in the middle of the base).  This ensured that the surface of the boss was exactly perpendicular to the lathe bed.  At this point I did not mill the top surface of the base, because I needed to establish the same front-to-back .010" height variation.  I needed to make an adjustable-height fixture, which is shown below.

The fixture is next to the moveable jaw of the vise, and is just a #10-24 bolt screwed into a threaded plate.  I turned the end of the bolt down to a rounded point, thinking this would ensure the base would ONLY align itself to the rod.  I adjusted the bolt until the top of the base had the same .010" slope, then milled the base.  This ensured that the top of the base was parallel to the lathe bed.

Next, I moved on to the top of the tailstock.  In this case, I extended the quill and clamped it in the vise, using the horizontal "vee" in the moveable jaw to establish the horizontal plane.  I also checked the alignment using a DTI and found it was OK.  I then adjusted the tailstock (bumping it with a dead blow hammer) until the mating surfaces were parallel to the milling head.  See below.

A quick check with the DTI showed that the two surfaces were not on the same plane, which would affect the vertical alignment.  So I milled off enough to equalize the two surfaces.  I also milled the vertical face that contacts the base.  This ensured that the quill would be parallel to the lathe bed.

After doing all this, I found that the tailstock was too low, to the tune of about .080 inch.  To address this I machined a couple of spacers.  This in itself was an "interesting" exercise because the spacers needed to be the same thickness.  I did it by machining a large spacer and cutting it in half.  I machined both sides of the stock to minimize the effects of warp due to stress relief (and also to address any tram related issues).

The tailstock alignment substantially improved after these mods.  It was a bit of a pain to set the alignment, but, since I'm not planning on turning any tapers, I have no plans at this point to add a tailstock adjuster.