[apalm]

Just started machining so forgive me. We are making parts out of 304 ss. The first diameter were drilling is .212 from a .250 stock going .520 deep with a coolant thru carbide drill. Then from .450 to 1.2 were drilling a .177 hole. We were peck
drilling the first hole and we were having issues with the second drill snapping. We thought we were having issues with the guide bushing but everything seemed to be ok. Researched an found most people saying there is no need to peck drill with a carbide drill so we took it out. Now it seems like were having issues with chips and the drills chipping and burning up at the tip. Any advice on speeds and feeds or in general appreciated. Sorry for the newbie question.

[MikeMc]

First of all, I ALWAYS drill the smallest hole first, its just me. I also always peck when the hole is more that 3-5 x drill diameter. I know they say you don't have to but I do anyway, and the world has not stopped yet. The second drill snapping could be from the rough surface left by the first drill at the bottom of the hole. With the drill chipping and burning, chipping would be the drill feeding too fast, the burning is either the speed too fast, or not enough coolant in the hole. When we drill 304ss (which we do A LOT), I try not to run any other high pressure coolant at the same time as the drill. We run about 1500 psi. SF is always at 138 fpm, and the feed depends on the drill manufacturer, and the diameter of the drill itself. I found if you follow the drill manufacturers recommendations to the letter, you will not have any problems. I myself would run the .212 at about .003, and the .177 at about .002.

[apalm]

Thanks a lot for the response were testing it out today!

[elsanch]

i have extensive experience drilling 304 and it work hardens.. i would drill the small hole first...peck with a tin coated cobalt drill..make sure the second drill also has the same angle as the first drill..(a mismatch in angles would cause you to burn at the drill tips more)...177 dia i would do 3000 rpm..peck .100..feed of .002...same for .212...you are only doing about .017/.018 bigger on 2nd drill......the cobalt drill will give you a lil more flexibility..whereas carbide is brittle.. try GHURING