Effect of drilling hardened linear rails?

[routercnc]

Hi Ross,

I think drilling the hole would be fairly straightforward, and I would do somthing similar to what you suggest - make up fore/aft sliding grinding jig to grind a flat spot. This gets through the hard layer, and provides a nice flat area to drill, counterbore, tap, whatever.

My concern is the act of drilling the hole, and whether there are any residual stresses in the bar which then give rise to distortion. These bars are precision ground to be straight and round. How much would this operation upset that? If they are not stress relieved (heat to ~1200F then cool very slowly I think is one method) then there is a risk.

Jonathan hasn't actually tried it by the way.

[GeorgeD]

Why does it have to be drilled?if we make a block like the pic below out of ally? fixittothe base/bed then place/clamp the rail on to this temporarily to get the precise height for the end support rail mounts.