In article , James P Crombie wrote:

The other thing you could do is reduce the cutting lip angle to reduce
the pull-through when it breaks through. Similar things happen when
drilling brass or bronze. You can reduce the angle to around 85-90 degrees

You certainly can do that, but I prefer not to modify the drill, myself,
because I'll just have to modify it back again later. It drills pretty slow
in stainless with flat lips.

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Mike Graham | Metalworker, rustic, part-time zealot.
mike 'at' @metalmangler.com |
http://www.metalmangler.com| Caledon, Ontario, Canada

I got some cast iron from Metal Express and milled a small cube, about
an inch in each dimension. Then I tried to drill a 1/8 inch hole
through it. Just as the bit was emerging, it broke. So I tried it
again, this time with lubrication, and the same thing happened. I do
not understand this. The cast iron is soft and easily drilled.

What is causing this, and what can I do about it?

Thanks,

Will

The other thing you could do is reduce the cutting lip angle to reduce
the pull-through when it breaks through. Similar things happen when
drilling brass or bronze. You can reduce the angle to around 85-90 degrees

Mike Graham wrote:

In article , Will Self wrote:


What is causing this, and what can I do about it?


Drill the cast iron with a backing-pad of mild steel. That will keep the
bit from breaking. What's happening is that the drill is self-feeding like
a corkscrew into the work. When you break through you lose the resistance
of the chisel-edge going through the work, you advance the drill too fast
and the edges catch. If you're drilling on the mill then a good way to
avoid this problem is to use the knee to feed the last bit. Drill most of
the way through then lock the quill and raise the knee to drill the rest of
the way. This also works in other ugly situations like when you're drilling
into a cross-hole.



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James P Crombie

Summerside Machinist
Prince Edward Island Amateur Astronomer
Canada 3D Designer

E-mail
Astronomy webpage http://www.jamescrombie.com
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"James P Crombie" wrote in message
...
The other thing you could do is reduce the cutting lip angle to reduce
the pull-through when it breaks through. Similar things happen when
drilling brass or bronze. You can reduce the angle to around 85-90
degrees

Actually, the recommended procedure us to alter the rake angle of the drill.
Drilling cast iron can be as challenging as drilling brass. Reducing the
rake tends to minimize the self feeding experienced as the drill breaks
through.

Mike's suggestion to use the knee is a good one, as is snugging the quill
lock on your mill as you come near the end of the hole. I rarely use the
knee idea, but I'm very familiar with my mill, which has a very nice feel.

Harold

On Sat, 13 Sep 2003 15:16:39 -0400, Mike Graham
wrote:

In article , Will Self wrote:

What is causing this, and what can I do about it?

Drill the cast iron with a backing-pad of mild steel. That will keep the
bit from breaking. What's happening is that the drill is self-feeding like
a corkscrew into the work. When you break through you lose the resistance
of the chisel-edge going through the work, you advance the drill too fast
and the edges catch. If you're drilling on the mill then a good way to
avoid this problem is to use the knee to feed the last bit. Drill most of
the way through then lock the quill and raise the knee to drill the rest of
the way. This also works in other ugly situations like when you're drilling
into a cross-hole.
You may find, Mike, that quicker than locking the quill and using the
knee to feed is to use the quill lock to put enough drag on the quill
so that the drill can't self feed the last bit. I do this all the
time.
ERS