If you are reading this forum I am sure you have been there... Late night in the shop, been working with some aluminum and trying to drill the final hole in a bracket or project, your hands slip a bit and SNAP! The drill bit has broken in the hole! An extractor will not grab, vise grips are useless as the break is below the surface, and heating is not working... All is LOST!
Now if you are like me, at this point you have gouged up the hole, cracked at least a couple beers and stared at it incessantly trying to come up with a plan, only to get mad and storm out of the garage trying to figure out where to get another block of aluminum...
BUT! There is another method to try before you give up on it. It is easy to do but time consuming and a bit size restrictive so you will have to weigh the time benefits, but it may be a lifesaver in some situations... You can actually DISSOLVE the drill bit out of the block without damaging the aluminum!
As I said, this can take some time and will take longer the larger the drill bit, but seems to work well in a few hours on smaller bits.
You will need to go to the grocery store (or raid your wife's spice cabinet, which she will completely be happy with after using the dishwasher a couple times to wash Jeep parts) for some Alum powder. This is a common spice found in the small spice containers by Tones or McCormick’s. Depending on the size of the part, you will most likely need a few of them so stock up.
To dissolve the part you will need the following:
1) Hot plate or stove
2) Disposable non-ferrous container (aluminum bread pans work well)
3) A quantity of Alum powder
4) Clean water
5) Aluminum block with busted bit
To start, clean the aluminum block. Remove all chips, grease, etc... And dry. Start the hot plate or stove. Add water to the pan and alum powder in roughly a 1 part Alum to 2 parts water ratio. Stir until the Alum dissolves. Now insert the block into the water and bring the hot plate to just under boiling. Loosely cover with foil and leave the part sit. Periodically check the water level and add as needed to keep the broken bit hole covered.
After a few minutes or so you should start to see miniature bubbles consistently rising from the hole that the broken bit is in. This is essentially rapid rusting the bit, while the non-ferrous materials remain unchanged.
Check the part after a few hours to see if it has broken down enough to remove it from the block. If it has not, continue the process until it has had the chance to work its magic. It will amaze you how fast it can break down the bit if done correctly. Keep running the part in the bath until it has dissolved enough to pull out or let it sit until it dissolves completely. Keep in mind that the larger the broken bit the longer this is going to take. In my experiences it has taken a day or more of running the hot plate to fully break out a large bit over 7/16.
This process is slow and time consuming but it pales in cost and time compared to making a complex part again. You can be working on something else while it works and save your part. It is a process used by watchmakers for years that has been proven time and again. The traditional process uses concentrated Nitric Acid but Alum powder is much more accessible and is much easier to fins at 2am when you are out of options… I have used this on complex machined components that would take hours or days to make again. If it means saving a complex bracket or an aluminum block or head to a motor it is well worth the time to try it. You really have nothing to lose as it will not damage the block it is in.
If the part is too big (such as a block), the proper method to do the same process is to create a "dam" around the hole using clay or some other type of water resistant putty. Just build it up around the hole and pour in hot solution. You can either heat the block around the hole or let it work cold. It will work cold but the heat seems to greatly speed up the process.
When you are done make sure to completely flush out the hole on the part or whatever bolt you insert will get some corrosion from the residue. This may not be much but why risk it.
Hope this helps someone out there who is ready to pull the little bit of hair they have out because they just ruined a couple hundred dollar spacer block or intake bracket.
A word of safety. You are dealing with hot water and Alum gasses. Please make sure to use proper safety procedures and do not breathe the resulting gas or get any on your clothes or skin. Wear popper safety gear when using this method.