We are close to finishing the Tom Senior light vertical at the museum. There is a bit of play in the X axis which requires attention, and the Y and Z aren't great. I have been conducting tests on the spindle which runs better than expected, and is now trammed square and is also square in the fore and aft axis.

Problems started when I started checking the Z axis moving the knee up and down. A dti was fixed to the column and one of the 2-4-6 blocks was clamped square to the bed Xaxis. The knee was sloping by about 0.010" in the 6" of the block.

It turned out that the pair of 2-4-6 blocks are not dead square. They both are three dimensional parallograms. They not only lean sideways, but fore and aft also. What clinched it was putting the long MT2 test bar in an R8 holder in the spindle. Including the taper, it is 11" long. and I have it running 0.0002" tir at the top and 0.001" tir at the bottom. When I set the blocks against the test bar it was obvious that there was a problem with the blocks.

On the surface table, the lean is easy to see with my square and even more obvious when toe bottoms of the blocks touch and there is 0.020" gap at the tops.

I also have some of the cheap 1-2-3 and 1-2-4 blocks (metric), surprisingly, they are actually dead square.

If I was still working, I could have got the blocks trued up by the grinders or the toolmakers in a jiffy.

I don't care what size they are, I can easily measure them if I need to. Making a cylinder square is only worthwhile if you start with ground stock.

If I had a cylinder square, I would expect it to be within 0.0001" in 8" of height on the diameter, and have a perfect finish, something I could not achieve by turning.