Spot Drilling/Center Drilling Steel 55 HRC

[JWB_Machining]

Hey,

I'm working with some decently hard steel, it ranges from 53-58 HRC. I need to create a 60 degree countersink on the ends of 7/32" Diam rods. I first tried doing this with a center drill and both ends broke, so I tried a 60 degree spot drill and just broke two of them. Anyone have any advice. What's an RPM I should use? I tried 200 and that didn't work so I went to 1000 and that didn't work either. I'm using my Haas TL-1 Lathe to do this and manually drilling in with my tail stock.

[beege]

What kind of center/spot drills are you using? Methinks only carbide will hold up against anything that hard. Slow is good here, even with carbide.

[JWB_Machining]

I am Using UltraTool Solid Carbide TiAlN Coated Center Drills and M.A. Ford Series 60 Solid Carbide Single Flute 1/4 60 degree Countersinks, I just broke on going at 50 RPM. Any Suggestions?

[Geof]

I think you are going to keep on breaking center drills or spot drills; the tip grind right at the point is not strong enough to take the forces need to make it cut material that hard.

What you could try is drilling a small pilot hole with a carbide drill then machine the taper with a very tiny tool; the very tiny tool could be something like a 1/8" two flute end mill.

I have used this approach on hard stuff but not that hard.

[JWB_Machining]

Well my boss man Said I don't have to put the countersink in since I'm having issues but how else can I support these rods when they're extended out 2.2" from my collet and I have to turn them down, I feel I'll get too much bending.

[JWB_Machining]

Is it ok If I use a 118 Degree Drill and then put my live center into that even though it's 60 degrees. I know this creates point loads but I can't think of any other way to support both end of these three inch rods when i have to turn down the center inch.

[JWB_Machining]

Could I use a Piece of Aluminum with the 60 degree countersink on one side and a 7/32 hole on the other and sandwhich that between my live center and my part?

[Geof]

.... i have to turn down the center inch.

You are not turning down the whole length?

Make an end cap with a 7/32 hole nice tight fit and the center hole in the opposite end and use this with a live center.