# Breaking drill bits



## jhanko (Dec 5, 2009)

I'm doing quite a bit of drilling on my mini-mill with 1/16" carbide drills. They are solid carbide with a 1/8" shank. I'm holding them in a MT collet. The problem is that every time I eject the collet (tapping the drawbar with a hammer), the fluted section of the drill snaps off of the shank from the shock of the hammer strike. I really don't want to use the drill chuck, as it just introduces more runout and lengthens the whole assembly. Any suggestions?


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## StrikerDown (Dec 5, 2009)

The shock of the hammer is causing the assembly to ring (vibrate like a bell) and this is snapping the bits?

I wonder if you used a soft face hammer or dead blow if that might help. 

Are you holding the drill bit when you strike the draw bar? Some of my Chinese collets don't hold well until tightened so I usually hold the tool on mine so it doesn't drop out and break a point or damage what it might hit. Holding the bit and hitting more softly might help with the shock. Just a thought, I have never seen this but have broken a few of those little fragile suckers though.


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## 65535 (Dec 5, 2009)

Use a copper or lead mallet. They won't send the harsh shock wave a steel hammer will.


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## precisionworks (Dec 5, 2009)

> the fluted section of the drill snaps off of the shank


Is the collet gripping the shank of the drill, or is it gripping on the flutes?


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## jhanko (Dec 5, 2009)

I have tried holding the bit while hitting. I ended up with the bit in my hand instead of on the bench. I'll try a softer hammer, it can't hurt. I'm holding the shank of the bit with a 1/8" collet. I think I'm going to thread the top of the spindle, so I can thread in a rod and "push" the collets out. I cringe every time I hit this thing. It can't be good for the gibs and bearings...


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## cmacclel (Dec 5, 2009)

Amazing I never thought hitting the draw bar would break a tool! Good luck.

Mac


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## jhanko (Dec 6, 2009)

I never imagined it could happen either. I couldn't figure out what was happening until I broke about five of them. I have broke over ten of them so far. Good thing they're only $5 for a box of ten on ebay. The bits are very small & brittle. I think making up a push bar solution is best.


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## will (Dec 6, 2009)

Have you tried leaving about 1/8 - 1/4 inch of the 1/8 inch shaft sticking out of the collet and then holding that part with a pair of needle nose pliers?


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## precisionworks (Dec 6, 2009)

> I cringe every time I hit this thing. It can't be good for the gibs and bearings...


Shouldn't be a problem. That's the standard way to dislodge any taper held by a drawbar. Some larger MT tooling has a wedge slot in the spindle, and a wedge is driven in with a 5# copper hammer until the tool drops. Neither one seem to affect the machine, and it's been this way since Morse taper & R-8 tooling was invented.


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## bluwolf (Dec 6, 2009)

precisionworks said:


> Shouldn't be a problem. That's the standard way to dislodge any taper held by a drawbar. Some larger MT tooling has a wedge slot in the spindle, and a wedge is driven in with a 5# copper hammer until the tool drops. Neither one seem to affect the machine, and it's been this way since Morse taper & R-8 tooling was invented.


 
I'm glad you said that. I was just thinking the same thing JHanko the other day when I was trying to get a sticky end mill out. I'm using a plastic face dead blow hammer.

Mike


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## Torque1st (Dec 6, 2009)

Try cushioning and catching the tool with a block of styrofoam.


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