I was recently drilling/tapping blind holes in 1/8" aluminum plate. Yeah, I know. I was tapping for 2-56 screws, which are just a tiny bit larger than 1/16" in diameter. I needed to about 12 holes and of course... I broke the tap. On the last hole. I had a lot of machining time invested in this small part, and I was on a deadline. I decided to try a trick I had learned years early from my sensei. I had never used the trick before on something so small, but what could I lose?
- Welder, TIG or otherwise.
- Thin Filler Rod (safety wire works well)
Step 1: Principles and Practice
Regardless of the size of the fastener, whether it's a chunky 1"-8 bolt, a pipe nipple or a 2-56 screw, the fundamental remains the same: build a stack of weld beads atop the stuck bolt/tap/plug. As the weld beads build up, you'll have a surface to grip with pliers. Alternatively, you can drop a nut over the weld-bead-stack, and weld them together- giving you a good surface to use a wrench or a socket [this is good for larger (1/4"+) fasteners].
I tend not so switch out the tungsten/collets/gas lens on my welder, so I used the 3/32" tungsten that lives in there. I did take the time to grind the point to a nice sharp (steep grind, like a pencil) point, that is not blunted on the grinding wheel.
With the machine set at 15amps, using .020 stainless steel safety wire as filler rod, I successfully build up a stack of weld beads. The trick is to make a puddle, add the material and then let it cool from red hot- a rhythm of about one bead every five seconds. Don't get it too hot!
Once you have a nice tall stack, let it cool completely. My experience has found that cooling naturally is the best bet. This is where the patience comes in. I have seen other cool rapidly with water. Honestly, I can't tell you which works better, but I know from experience that the slow cool method works.
Step 2: Extraction and Extra Tips
The added heat from the welding really helps free up the offending tap or bolt.
Once it's completely cool, feel free to add a little penetrating lube just for redundancy's sake, then attempt to extract the misbehaving tap. It's a good idea not to try to take it completely out straight away. Work it back and forth a few times, and test the resistance. If you're trying to get out a broken tap, it's likely to have broken due to the flutes being jam packed with chips. Take you're time, working it back and forth, adding more penetrating lubricant as needed.
- You can use any welder for this method: I've even used a stick welder (stainless steel 1/16" rod) to remove a 6mm bolt from a cylinder head.
- Sometimes, despite your best efforts, the stack of welds snaps off. Sometimes you don't get good penetration from the weld, or sometimes the tap is just jammed too tightly. If the stack snaps off, clean off the penetrating oil (if used) with compressed air or a solvent like Brakleen®, and try again. I've had to weld stacks two or three times before it finally worked.
- Take your time, and rejoice when you succeed!