Hi, I will be using a solid carbide drill for the first time, just want to get some input on feed and speed for it. I will be drilling a .422 dia hole for a 1/2-13 tap, in round bar. Round bar is .875 dia, and is 4140 HRA. I am using a cobalt twist drill now - we centerdrill, drill, c-sink and tap. But with the solid carbide drill, should i use a center drill? I can sacrifice a lower feed n speed if it will increase tool life, I'm not in that big of a hurry!

Carbide likes running at higher feeds and speeds - babying it might increase the life but I doubt it will have a substantial impact.

Center drill? I suggest it as a general rule. Solid carbide drills have a thicker web than a typical drill - depends on the manufacturer. They are stiffer though and are less likely to walk but on round stock they still can. I would center drill - it's just a good habit in my opinion.

Scott

Is this on a CNC lathe? Are you using soluble oil with chlorine? 3 or 5 diameters deep? With a short 3 diameter deep drill, you can usually skip the center drill. Is the drill coated with TiALN or TiCN or TiN? Split point? Best case: 3x diameter, soluble oil with chlorine, TiALN coated with high performance split point. For those conditions, you could run 400 sfm (3000 rpm) and .012"-.014" feed per turn (36-42 inches per minute) with good tool life. Even backed off to 300 sfm, it's still a fast hole. If I were tapping 1/2"-13 blind in 4140, I would drill a 7/16 hole. The stress on the tap and likelihood of breakage is a lot lower.

Dave

It's in a cnc mill, no coating, and it's a split point. Its straight through the part, not a blind hole. Flood coolant. I'm guessing i shouldn't peck drill.

Thanks.