This is my first post, please let me know what you think?
Have you ever had to drill a small diameter hole several times diameter? Broke multiple tools and had the drill wonder? Take a look at Mikron Tool, they have micro drills up to 50X diameter. Start with a pilot drill to start the hole straight, then an intermeadiate length drill and then your final length.
I just worked with a customer on a 300 series Stainless Steel application drilling 30X diameter. They had attempted this with other brands and broke many expensive drills. They were taking about 10 minutes per hole in the CNC Lathe and then switched over to the mill with a 8 station fixture. The tool holders were borderline for TIR(Total Indicator Runout) at .0002". The best would be .0001" TIR, at a .040" diameter would increase tool life and consistency. We had to clean, assemble and hand tighten before using a wrench in order to get the best results.
The TIR of the machine spindle is important as well, the more runout you have, the more stack tolerance you have to deal with. I recommend that machine shops should have their own certified precision test bars on hand in order to qualify the spindle. They should also have a force gage that measures the tool retention force of the spindle.
Back to the application, we ran the first set of parts reaching down through a counterbore. We dropped the cycle time to 12 minutes(incl. load & unload) for eight parts. The counterbore created a problem with chips, as we retracted the drill the chips were likely dropping back into the hole. Without high pressure coolant the chips weren't coming out like we'd like them too. We ended up drilling the parts from the opposite side of the part where the chips were unrestricted. This elimated the recutting and binding of the chips.
What has your experience been drilling small diameter deep holes?