CHAMFER FOR TAPPED HOLE

I am a bit vexed i have a double sided center drill i mic the shank to be .435 and the small od to be .185 I want to chamfer the hole before tapping it and I am finding it difficult. any help would be greatly appreciated

sorry I meant double end center drill

Is it a lathe center drill w/ the small starting tip. Or NC mill spot? And what degrees?

Most combination center drill countersinks are standard sizes. Refer to Machinery's Handbook for those sizes. Use the attached Excel sheet to calculate depth.

As always you got it right txcncman and thank you

I was a little pre mature I still dont get how to fill in the dialopg box to edit that tool and how do I use the excel to calculate the depth needed to leave a chamfer on the tapped hole please excuse my ignorance I am trying real hard to understand
andd this is for a vmc not a lathe

What size hole are you actually tapping?

So when you edit your center drill, Mastercam doesn't know how to calculate the depth on the hole calculator to leave a chamfer.
Ive only ever used nc spots, and the calulator works great for me.

I know its preference, but why are you using a lathe centerdrill instead of a nc spot drill?

This would be an example for a 3/8-16 tap. For the center drill, I put in 82 degrees, #7 center drill, 0.385 chamfer size and got 0.3276 for the center drill depth. This is usually not deep enough because it does not take into account the flat at the tip of the drill. But you can run the process on the machine and stop and measure and adjust Z depth from there.

These days I use Spot drills about 90 percent of the time. I hate using center drills.
Dcutler, how do you do in in gibbscam or bobcad do they have an easier way?

Gibbs cam has dialogue boxes defining the center drill and allow you to set the depth easily its been a while since i used bob cad

You can use a center drill / spot drill and define the depth as needed.

http://s13.postimage.org/isq79inuv/chamfer.png
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