Drilling advice on CNC Lathe

[motter71]

We have recently moved a drilling job from an old W&S turret lathe (1950's) to a CNC turret lathe (1985). I love the results I am getting, but I wonder if there is more to get. We are currently using a combined drill/countersink to get the live center of 1.5" diameter CR that we are drilling. We then go to a HSS 11/16" drill to countersink in app. 3/4" from the face of the material. We then go to a letter size "C" HSS parabolic drill to a depth of 3" from the face of the material. I know that carbide drills will give me faster feed rates and shorter run times. Could I use an 11/16" end mill for my countersink instead of my HSS 11/16" drill with better results? Are the carbide drills worth the money? Any drilling/machining tips and/or advice would be appreciated. I am also just looking for any fresh ideas or suggestions.

Chris

[HuFlungDung]

An insert drill would work quite well to open the hole without center drilling , if you have the rpm and horsepower for it. An 11/16 endmill does not have good drilling geometry compared to a drill. I like Kennametal drill bodies, but I suppose there are many other equally functional equivalents.

You should have through the coolant feed for the drill, although flood might be adequate for a shallow depth like 3/4" deep....it is riskier though. This drill should drill from solid.

For the size "C" drill, the previous insert drill (or endmill) will likely not give a good starting point. You may need to spot drill at the bottom of the 11/16 hole before continuing with the C drill. Carbide might be stiff enough to start without the spot, but it will not stand very much deflection either.

Do you have enough rpm on this machine to take advantage of the carbide? The 11/16 insert drill might need a minimum of 1500 rpm, maybe double that. The C sized carbide drill will need lots of rpm, too.

[motter71]

HuFlungDung,

Thank you for your prompt response. My machine has an RPM limit of 4000. That puts me right at the edge for a carbide letter "C" drill (I believe that 3900 rpm is recommended). I appreciate the tip about the insert drill. I use one on my VMC and I like the results I get with it. Thank you for the advice about using an end mill for my application. We'll steer clear of that.