Millstone dressing

To improve upon my mill project I ordered a set of 250 mm composite millstones from the Danish company Engsko.  Unfortunately, the millstones would not produce good flour in the mill.  I made several attempts to carefully line up the stones, shimming the mounting of both the bed stone and the runner stone, and finally "tramming the spindle."  No matter what I did, the mill would not produce good flour.

So I eventually concluded that the millstones as delivered were not properly dressed.  My own hunch is that these stones warped at some point in the curing or aging process.  The 250 mm stones are very small and I suspect this company does not sell that many of them.  Anyway, I pulled the runner stone off the shaft, which was a giant pain since my homemade keyway had welded the fitting onto the shaft.  I really had to pull hard on the harbor freight bearing puller, but remarkably it worked and I got the stone slid off.  Here is what I found with the straightedge:

Both the runner stone and the bedstone are high in the middle.  

This is a combination of old school and new.  I painted soot and linseed oil onto a stick of wood that I jointed to be perfectly straight.  By dragging it across the stones you can see the high spots.  In the above pictures, before I started, you can see how little of the stone was actually available to grind flour.  They are almost 1 mm high in the middle!

Here is how it was looking after a few grindings.  Not nearly flat enough, as it turned out.  But it sure seemed pretty flat to me at the time.

I eventually converted the mill to run with the lower stone as the runner stone, which I discovered is the modern way of building a horizontal mill.  The eye stays cleaner and it seems to draw grain in more evenly.  Anyway, the mill ran a little bit better but it was clear that more aligning was in order.  Here I am using a dial indicator to align the runner stone to the shaft.  I got it even to within a couple thousands of an inch. 

But it still wasn't good enough.  I began to suspect that the landings were getting too glazed from the angle grinder, so I went at it with a pick to roughen up the lands.  A brick hammer is working pretty well, as long as I sharpen it regularly.

It's getting closer to making flour, as you can see the white powder in the below picture.  But it has to be better, so now I am painting the stones with food coloring, running them together, and then hammering away at the places where the stones touch.  I'm learning a lot about millstone dressing!  Will report back when it's finally working well...