How extract a broken #49 drill bit in Aluminum

B

Bill Kahn

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This must be one of the very most common beginner questions. Please refer me to any previous threads that talk about this.

I was drilling a blind .9" long #49 hole in a 2x2x1.1" rectangular piece of aluminum. (Using my mill) First one went fine. In second the bit snapped off deep in the hole.

Is there any way to save the piece? (No other location for the hole will work.)

Thanks.

-Bill
 
This is always a tough one. So... I've put my kevlar on, so start shootin'!

There is a cost/benefit to consider here; the amount of work and cost in the part versus the amount of work and cost to save it. There may also be an intangible benefit of additional experience in redoing the work.

Commercial companies remove drill bits and broken taps by eroding them - a speeded up EDM process - BUT - in such a small hole damaging the sides of the hole is inevitable.

Here's the save analysis: Aluminum will expand much more than steel at elevated temperatures. If by heating it to 250 degrees F, it doesn't fall out or move with a fine piano wire hook, then the tip is stuck with wedged swarf. Your piece is then toast no matter what you do. Why 250? because this is getting dangerously close to altering the characteristics (temper, heat treat) of the aluminum (assuming it is 6061).

I hope this 'helps'...
 
Sorry to hear that. Dabbler beat me to the oven / expansion trick so I will proceed to another friendly suggestion you might receive involving boiling the part in a solution of saturated alum powder to eat away at the bit. Even some YouTube videos showing it working.

I broke a tap in a 2041 part & had a horrible time with that particular extraction method (link below). It may well be related to the tap composition/coating. But my own opinion: depending on a bunch of variables such as how badly stuck, how much swarf packed in the flutes, the type of drill, availability of alum & suitable boiling vessel... start working on the new part :)
http://www.homemodelenginemachinist.com/showthread.php?t=26470

I find peck drilling method + those high angle fluted drills + lots of WD40 or aluminum friendly cutting fluid works best. Small drills are very sensitive to run out so if your chuck jaws are sloppy, that invites problems. When you do the calculation for ideal speed your mill is probably on the low side if its anything like mine. Good luck.
 
First I would try banging it hole side down on a piece of wood. I have about 80% success with that.
 
I have always herd that you can put a dam around the part and soak the part in a solution of alum it will desolve the steel and not the aluminum. I have some alum powder but have never tried it and it is a slow process.
 
Was this going to be a through hole? If so, you can try drilling from the back side. When you hit the broken drill, you may just pop it loose. if not, take a piece of piano wire slightly smaller than your drill size and gently try to tap it out. If the exit hole size isn't critical, you can use a larger drill which will improve your chances of properly hitting the broken drill.
 
This doesn't help your extraction problem, but its an interesting subject to me. Like how gun barrels are drilled etc. Your #49 drill is .073 diameter, so at 0.9" penetration you are dealing with a 12.3X depth : diameter ratio. There are all kinds of tables out there, maybe you will find some specific to aluminum which is sticky stuff.

If there is any way to re-tool your design so you don't have this issue, that would be optimal. If it is what it is, then there e are some specialized drills out there, this is one link I saved.
http://www.guhring.com/Documents/Catalog/Drills/DeepHoleFlyer.pdf
 
Alum will work but Nitric acid is faster. It will dissolve the steel and not the aluminum. Neither of these is particularly fast!
Robert
 
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I used alum to remove broken 4-40 taps in aluminum.

In order to get useful removal speed, the alum needs to be supersaturated and near the boiling point of water. Depending on the size of the piece, find a container that you can put on the stove double boiler style. Over the course of 2-3 days, you are going to be adding water to the double part of the boiler rather regularly, and adding triflings of water to the alum part containing the piece under bit-removal less regularly.

Last time I did this, the part fit in a glass glass, and I set the glass in a typical fry pan with 1.5" of water on a low boil. When I was done, I left the glass cool off and within a day the rest of the water in the glass evaporated and I have a complete glass of crystalline alum left in the glass. It looks like all I have to do next time is to add about a shot glass of water and a bit of heat to get the alum liquid again.
 
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