I'm drilling a 1 3/4" hole 42" long on a copper bar, 21" from each end. No, tube isn't available. Anyways, it is a standard black oxide twist drill and it has done several of these parts now. The problem is the drill seems to be making a hole slightly smaller than the drill, it is tight on retraction for several inches. A present the hole is about 14" deep and when you retract it to clear chips as it re-enters the hole it goes easy for about half the depth, then gets very hard for the next several inches until it hits the depth to actually start drilling again. I mike'd the drill OD and all seems well except scuffing on the last inch of the major OD. After stoning those edges I blued them and after one short drilling all the blue was gone from the narrow OD land. The hole isn't critical for dia. or finish and I'm thinking about relieving the OD except for the last 1/2" near the tip.