Re: [CAD_CAM_EDM_DRO] Re: Flat Holes

Hi GM4T:
What Fred Smith was suggesting is that you don't bother making a
flat-bottomed hole, you simply take a regular twist drill big enough for the
bolt head, and poke it down the hole for the bolt body, until it's deep
enough for the bolt head to be flush.
You end up with only edge contact between the bolt head and the bottom of
the hole, but for many applications---WHO CARES!!

If you do want or need proper contact between the bolt head and the hole,
the flat bottom drill is one way to get there.
However, despite it's name, it is not just ground flat on the end!!
It has to have a specific shape to make it cut.
I mentioned in my last post to you, that the easiest way to see what the
drill tip has to look like is to look at the end of a 2 flute endmill.
That's the shape you have to grind on the drill tip.
It's not nearly as difficult as it looks, and you only need to get the
geometry correct on the outer halves of the cutting edges.
You don't need to care a fig about the center because you've drilled for the
bolt body already, so the inner half of the head sized drill is only cutting
air anyway.

Cheers

Marcus
-----Original Message-----
From: gm4ta@... <gm4ta@...>
To: CAD_CAM_EDM_DRO@yahoogroups.com <CAD_CAM_EDM_DRO@yahoogroups.com>
Date: Saturday, November 10, 2001 6:41 PM
Subject: [CAD_CAM_EDM_DRO] Re: Flat Holes

>You got it 100%. I only have a drill press. I think I'm going to use
>the 2 drills method now. But if I grind flat the bottom, then the
>bottom won't have any cutting action. Would that matter since it's
>going to cut a little bit anyways?
>
>-GM4T
>
>
>
>--- In CAD_CAM_EDM_DRO@y..., dougrasmussen@c... wrote:
>> GM4T,
>>
>> Unfortunately, you didn't get much useable advice from the group.
>>
>> First off, you don't want flat bottom holes, you want
>counterbores.
>> And there are common tools which cut them for your cap screws. You
>> won't find them at Home Depot, though. Good counterbore tools
>aren't
>> cheap, either.
>>
>> I'm assuming since your machining knowledge is limited, you
>probably
>> don't have a milling machine so the use of end mills is ruled out.
>> You probably have a drill press, right? But you can't use end
>mills
>> in a drill press.
>>
>> The best advice I've seen for you is that from Fred. Use two
>drills
>> like he suggests. It's a very acceptable solution that's easy and
>> the price is right.
>>
>> Doug
>>
>>
>>
>> --- In CAD_CAM_EDM_DRO@y..., gm4ta@i... wrote:
>> > Thanks everyone for their reply! I can't believe how much I'm
>> > learning from this group. At first I thought that there is no way
>> of
>> > making my guitar bridge. But now as I gain more knowledge on
>tools
>> > it's becoming much more possible. The next thing I'm going to buy
>> > when I go to Home Depot will be an 2 end mills: one for the 6-32
>> > socket head cap and one for the 4-40.
>> >
>> > Thanks again!
>> > -GM4T
>
>
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