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
Rhinoceros 3D webpage http://www.jamescrombie.com/rhino/
Mirror Grinder page http://www.jamescrombie.com/pics/
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