Re: [CAD_CAM_EDM_DRO] Re: Flat Holes

Hi G4MT:
Plunging with an end mill on a flimsy machine like a Sherline or a
mill-drill is EXTREMELY DANGEROUS!!!
End mills have side cutting flutes and can grab the side wall of the hole
while cutting.
The result will be a tremendous bang, accompanied by a ruined part, a broken
tool, and a little brown stain in your underwear if you are lucky.
If you are not lucky, you will be visiting the hospital.
I cannot emphasize this enough NEVER plunge with an endmill on anything
lighter than a Bridgeport.
Lots of guys get away with it for years but it is BAD BAD BAD!!!
The correct tool to use is a counterbore; the pilot will prevent excessive
runout and the flutes have no side relief so they can't dig in.
Be very careful if you are machining brass: brass is very "grabby" and will
yank the job off the table in a heartbeat if you don't have it well secured
to the table.
There are a couple of ways to prevent this; first, stone a small "land" with
zero rake on the ends of the counterbore, or better yet, get a zero rake
counterbore specifically for brass.
Second, never feed with the quill; lock it and feed up with the table on a
knee type mill.
(on a Sherline, of course, you don't have a quill.)
And always have your job secured to the table with at least two clamps, or
securely in the vise.
Don't EVER hand hold a drilling or counterboring job in brass!!!!!

If you are in a pinch, and can't get a counterbore, a flat-bottom drill will
do in a pinch.
Take a 2 flute endmill and look at it from the business end.
That is the shape you have to grind onto the end of the drill.
The difference is, of course, that the drill has a narrow land on the
periphery but no side relief.
That means it can rub against the side of the hole but cannot dig in like
the endmill can.
When you use a flat-bottom drill, you MUST start the hole with a regular
pointed drill of the same size, and drill deep enough that the entire
diameter of the drill is buried in the job at least 0.050" or thereabouts.
If you don't, the drill will catch on the workpiece as soon as it contacts,
and will bend or break, while making a total mess of your job.
A short, stiff, flat-bottom spotting drill in a collet can be run into a
chamfer if the mill is really rigid, but on a hunky mill you can get away
with an endmill too, if your setup is very good.
By the way, the same rules apply for drills in brass; they tend to grab like
crazy unless you stone a zero rake land on the cutting edges.

Forgive the rant on this, but I couldn't let this one go by without a
comment.
WORK SAFE...HAVE FUN.
Cheers

Marcus
-----Original Message-----
From: gm4ta@... <gm4ta@...>
To: CAD_CAM_EDM_DRO@yahoogroups.com <CAD_CAM_EDM_DRO@yahoogroups.com>
Date: Friday, November 09, 2001 6:53 PM
Subject: [CAD_CAM_EDM_DRO] Re: Flat Holes

>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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