Z-axis Plumb

[Simops]

Ok at first I was not going to post this because felt, as this has been thrashed before (yes have read all the posts I could find), that I should be able to sort this out myself, but damn I'm going to ask for your advice anyway!

Its to do with my Z-axis. When I surface my spoiboard (use a 2.5" Amana RC2257) I get a slight ridge along the Y-axis. Pleae note that my Y axis is factory default X-axis (see pic attached). Brady says that if you can hook your nail it means the spindle is not square. I have measured my nail hook at 5 thou.

If I do as Brady says in one of his posts and use a square against the Spindle I find that this is not accurate for me as my Spindle does not have parallel sides, that is, placed against the left side (which is the side I used to initially square the spindle) shows dead square but then if I use the square on the rght side it is not. It should be the same if the Spindle has straight parallel sides, see pics bellow.

Ok so I decided to chuck in a 1/2" rod (that is a perfect straight rod) into the collet. And place a square up to that. It shows square all round. But then this may not be accurate enough reference as only over a small distance. So I can't rely on the use of a square to 'square' the spindle it seems so will use the surfacing as the guide. No ridges = perfect square.

Indications of having ridges along my Y axis says that I have to adjust the Spindle by unscrewing the 6 bolts holding the Spindle carriage and turn it right as I look at it to square it up. But of course there is no further adjustment available. Before I go to doing something radical as suggested by Gary to make the holes larger or Daniel's Tramel adjustment device....is 5 thou acceptable or am I being to pendantic by trying to get it less than 5 thou??

Thanks

Mike