Worst case scenario pin and screw removal- EDM machining in gunsmithing
At the shop we tend to be exposed to some pretty unique challenges. Being the only full-service gunsmithing machine shop on an island with some 7.6 million people on it, means you are the last resort after some other well meaning individuals attempt repairs.
We’ve heated, cooled, pressed, drilled, milled, and hammered out more mistakes than you could imagine. Sometimes we get some that are nearly impossible.
A customer brought in the toggle link for a completely correct 1938 Luger P-08 pistol. The tapered toggle link pin that passes through the link was seized in place and he had attempted to remove it. I brought it into the shop and found it wouldn’t budge. A hammer and punch weren’t even close. Heat, not working. I made a fixture and tried to press it out. Nothing.
The pin is fairly small, .279″ long, tapering from 0.059″ at the top to 0.056″ at the bottom, which is significantly smaller than the screws and pins we’d usually drill out. Initially I considered spotting the center of the pin and trying to center drill it with a .~030″ through-coolant carbide bit. I was worried the bit would walk and we could lose the part. After chatting with the applications engineer next door, we decided to take it to an EDM shop that we’ve used in the past and have them burn it out.
A quick note about the P-08 toggle pin, IT GOES IN FROM THE TOP. DO NOT try to drift it downward. Also, if you tap it once and it doesn’t move, bring it to a gunsmith. Hitting it too many times can result in mushrooming over the small end causing a mechanical lockup holding it in place. This would be bad.
Electrical Discharge Machining uses electricity to carry away pieces of metal to form a part (for a more detailed explanation, check out Wikipedia). In the world of EDM machining you have wire EDM machines, EDM drills, and sinker EDMs. In this case we used the EDM drill and sinker EDM.
Our first strategy to remove the pin was to burn a hole through the middle and see if that would relieve the pressure and allow the pin to pop out. Ken, the super EDM machinist, indicated in on the pin and EDM drilled a .030″ hole through the dead center of the pin.
You can see the hole in the image above. It is small, and we managed to get it to pass through the exact center of the pin. When we tried to drift out the tapered pin, it still wouldn’t budge. Onto the next strategy.
Sinker EDMs use a custom cut graphite electrode to form metal parts. Take a look at the image above. The black graphite electrode in the center of the picture was used to form the metal part below it. Ken felt that our next move would be to make a custom electrode with the same taper as the pin and use that to remove the rest of the pin.
He made up a tapered pin electrode and used that to burn out what was left.
It worked fantastically well. The custom electrode is shown beneath the salvaged toggle link. The part was set up so well, about 80% of the taper pin hole still had the original 1938 bluing in it.
Since the EDM machine is touchless, meaning it doesn’t actually have a part of the tool that touched the metal, the surrounding surfaces were perfect.
This gorgeous pistol will remain in 100% correct condition for future generations.
If you have a rare firearm with a seized pin or screw, contact us at 782guns.com to see if we can help. It is an expensive process, however, for certain firearms, it may be the only way to save them.
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