Rookie Mistake- broken drill bit

dulltool17

dulltool17

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I'll put this here because I should have seen it coming....

Drilling two cross holes 1/16" Dia in 4140 HT. broke the bit as it crossed the first hole.

Drill is/was HSS

? will a solid carbide end-mill remove the remnants?

Broken piece of the bit appears to be ~1/8" long
 
That should work. be careful not to break the carbide in there too.

In general, if its not a valuable large number of hours part, i just start over when breaking a cutter in the work.
 
dulltool17 said:
Drilling two cross holes 1/16" Dia in 4140 HT. broke the bit as it crossed the first hole.

Drill is/was HSS
Click to expand...
Hate when that happens. Could you drill hole #1, plug it with steel wire, and then drill hole #2
through the plug? It'd soften the cut interruption that probably caused the break.
 
Flip it and drill from opposite side.

Be careful to greatly reduce feed when you get to near chunk.

You should be able to determine that be placing part in vice and using broken bit in chuck.


Flip then peck drill when close and when it just starts to break through get music wire to punch it.

Sent from my SAMSUNG-SGH-I337Z using Tapatalk
 
Find/make a punch of suitable size and get in there and mash the carp out of the broken drill bit before approaching it with the carbide. Knock all the shards down.
Depending on the part and as Karl pointed out, I would be inclined to fill it with lead before completing the cross drilling.

Cheers Phil
 
Thanks for the replies, guys-

- did drill from opp side. Now I have exposed flutes from both sides. At least I know where the tip is.
- as for the idea of breaking the end mill.....thought that might be the case. Thanks, RJ, for confirming that thought.
- I tried to use the remaining drill shank as a punch, but broke that too.

I think if I can get a stout enough punch, I'll try to punch it back through the way it went in initially.

Again, thanks, guys. Hope I can give some decent advice in return.
 
(about drill broken in hole)
dulltool17 said:
. Now I have exposed flutes from both sides. At least I know where the tip is.
- as for the idea of breaking the end mill.....thought that might be the case. .
Click to expand...
One kind of drill that WON'T break, is a soft (brass works) rod with a little abrasive grit. Make
a glycerine/water/grit slurry, paint it into the hole, and gently stir it into the hard bits with the
brass 'drill'. Keep backing out and adding grit, and don't push too hard, it'll go through. Eventually.

Ultrasound drilling (similar grinding technique) and EDM will also work, but it's unlikely those
are available...
 
If the punch doesn't work, I'll try some valve grinding compound on a brass rod.

No EDM, as you guessed, but this would be a great case for having one..
 
whitmore said:
(about drill broken in hole)
One kind of drill that WON'T break, is a soft (brass works) rod with a little abrasive grit. Make
a glycerine/water/grit slurry, paint it into the hole, and gently stir it into the hard bits with the
brass 'drill'. Keep backing out and adding grit, and don't push too hard, it'll go through. Eventually.
Ultrasound drilling (similar grinding technique) and EDM will also work, but it's unlikely those
are available...
Click to expand...
that is a very cool trick!
i'm going to put that in the back of my head!
thanks ;)
 
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