I'm wondering how some of you accomplish this. When drilling holes for sights and things do you square up the bottom and how do you do it?

John,

I basically turn a twist drill into a flat bottom mill. I grind it flat, and then with a diamond stone, hand cut a relief angle on each half like a 2 flute mill.

You can buy suitable countersinks from Forester or Brownells

I use a two flute mill, but I do that kind of work in bridgport.

If I don't have a mill that fits, then I make a flat bottom drill like shown above.

Those countersink that Duane is talking about work, period. And well worth the money. They can be had in 6-48 or 8-40 size and flat bottom or Weaver style countersink.

You can also get step drills from J&L for the same purpose.

I think he's asking about a flat bottom in the threaded portion of a blind hole. A #6 Weaver countersink won't do much for that application. Westpac's suggestion looks like a good one. I'm going to try his idea of hand stoning the relief angle. Lord knows I have a drawer full of junk drill bits.

quote:

Originally posted by M Pursell:
I think he's asking about a flat bottom in the threaded portion of a blind hole. A #6 Weaver countersink won't do much for that application. Westpac's suggestion looks like a good one. I'm going to try his idea of hand stoning the relief angle. Lord knows I have a drawer full of junk drill bits.

HMMM, then why would you even care if the bottom was flat. I never even considered it. I am humbled.

Actually, I thank both Malm and Duane for there input even though they're for two different situations. I have a complete set of the countersinks for burying screw heads and now I have a great technique for squaring the bottoms of drill holes prior to tapping. I've been hanging around here for 7 years now and I continue to learn new things here almost every day.

My thanks to all,

quote:

Originally posted by Jim Kobe:

quote:

Originally posted by M Pursell:
I think he's asking about a flat bottom in the threaded portion of a blind hole. A #6 Weaver countersink won't do much for that application. Westpac's suggestion looks like a good one. I'm going to try his idea of hand stoning the relief angle. Lord knows I have a drawer full of junk drill bits.

HMMM, then why would you even care if the bottom was flat. I never even considered it. I am humbled.

Well, when you only have this much room for threads > <, you don't want to waste this much room > < on the pointy end of the drill bit.

As i need them, I've been making single lip "D" bits out of O1 or W1 and hardening with a torch. I can make them just over the head diameter and they cut real well in the mill. I have had chatter problems in a drill press with a less than rigid setup.
Greg