I need o make several deep holes on 1.2343,of 3 diameter with a depth of 143 mm and must achieve no more than 0.02 of hole deviation.
So far, best i could do, was a 2 step process with a carbide drill and a gun drill after to reach the desired depth.

First i drilled 90mm with a carbide drill with inner cooling, then used a single flute gun drill to reach the final depth of 143mm. My problem so far is reaching the desired hole deviation, best I have achieved so far is .1mm deviation from top to bottom.

I am doing this on a brand new CNC machine with inner cooling with Kennametal carbide drill and botek gun drill.

Does anyone have a useful tip on how to improve this?
PS: this is not a breakthrough hole.

Thanks for any help!