I would give these guys a call.
I am trying to drill and/or bore a 20.58 hole radially on a live tooling lathe into 4140 prehard 32-40 Rc. Its a tight size tolerance of ±0.015mm with a micro of 1.6Ra. So far drill , reaming, or single point boring has failed. Anyone have a solution for this Micro other than second operation grinding? This is a high production job running from bar stock and the radial hole is through the part 64mm in diameter.
What about gun drilling
That is a big hole considering you are doing it with live tools in a turret.
You did not tell us what type of drills you are using. OSG Max series drills are capable of drilling your hole and holding size. I am no longer calabrated to Ra surface finishes, you might have trouble.
Criterion makes a boring bar that would be ideal for that application. The bars are similar to the standard lathe bar except the head is adjustable. I do not know if they have one small enough to bore 20mm. Mine is 1.25 diameter. You might check with them.
Mapal can supply a tool that will ream the hole and leave the desired finish. Get the check book out, they are very proud of their tools.
Let us know how you fix the problem.
A metric 1.6Ra finish isn't all that fine, about equal to 63 microinch. This should be easily obtainable with the right drill, no need for extraordinary methods such as grinding or burnishing.
If the 1.6 Ra is equal to a 63 MIF then the OSG MAX series should be capable.
I used a fullerton dominator drill. Its a double margin drill probably like the OSG max but cheeper. I had to have it Tialn coated and achieved the micro of .5 Ra. thanks for all of the help guys. I really didn't want to burnish it.