I have a one-off job to put some extra 3/8" UNC threads in an expensive marine item - so want to do the best I can in preparing for this
Task is to drill a small number of 5/16" blinds holes (3/4" deep) in6061 T6 Aluminium
Recc Cutting speeds using this table (and calculator)
Shows as 7334 rpm, my bench drill which has Max of 2580 rpm so assume I should go with that. I'll use appropriate cutting fluid ....
I have always in past when accuracy required - drilled undersize (by about 1/16 on this size hole) - then opened out hole to final size on a second past with the 5/16 drill. Almost using final drill as a reamer.
I was recently berated for this with advice that I should just feed in final size drill and do it all in one pass ... better accuracy.
Welcome advice on best approach.