John Coloccia
12-05-2012, 6:01 PM
Just wanted to post a little technique I use sometimes when things really go wrong. I think a lot of old timer machinists have probably seen this, but it's rarely talked about and can really save your bacon some day.
Anyhow, my first thought is always to try wedging the next size up allen key in there and see if it moves. For example, this is an M4 (4mm) bolt. Next size up is 1/4" hex key...you often have to go to a different system to get a good fit. Anyhow, that didn't work. Why? Well, this was on a motor coupling. These usually NEVER come off for the life of the machine and you tend to really crank down hard on them. No way this was coming out with that trick. Next thing I tried was a screw extractor. Drill through the head, twist it in and out it should come. I happened to have a kit laying around...not sure for what since I rarely ever need on, but there it was. My first tip off should have been that one was missing. Well, now two are missing, with the other half of the one I tried tonight buried firmly in the bolt. Here's a little hint....don't buy cheap, Chinese extractors. Despite being absolute garbage, they are still hardened like taps and there is no way in the world you will ever drill it out. This severely limits your options, as option #3 is usually to drill the head off and then there are any number of ways to gently drive out the screw once the pressure is relieved. Now that's impossible because the extractor is in the way.
Here's the victim. You can see I've already started doing something to it. Documenting this was an after thought. Note the little dimple on the head to the left. That's a center punch.
247174
Now I drill a 3/32" hole through the side of the head. It's fairly important that you drill straight and don't wobble too much. Here's where having a good feel for drilling freehand can really turn an otherwise show stopping heading into no big deal.
247175
Why 3/32"? Well, this ain't my first rodeo and I just happen to have a broken 3/32" drill bit laying around for just such an occasion. On a larger bolt, use a larger bit. I often keep old bit around for things like this. I also use them as alignment pins...what better alignment pin to stick in a 1/4" hole than a 1/4" drill shank? :) I suggest you break or cut it off at the flutes as it WILL break there anyway and it's potentially very dangerous.
247176
Grab my spoke, give a little turn and presto. From major problem to minor inconvenience in just a few minutes.
247177
Now, you may only get a 1/4 turn. That's not enough, so you have to so this multiple times. If your drilling is sloppy, you will need to really slow down and concentrate or will run out of room very fast and have a hard time getting this to work. This particular one took three spoke holes until I could grab it with pliers and pull it out.
247178
Hope this helps someone when you have a difficult extraction to do with partially buried bolt head. :)
Anyhow, my first thought is always to try wedging the next size up allen key in there and see if it moves. For example, this is an M4 (4mm) bolt. Next size up is 1/4" hex key...you often have to go to a different system to get a good fit. Anyhow, that didn't work. Why? Well, this was on a motor coupling. These usually NEVER come off for the life of the machine and you tend to really crank down hard on them. No way this was coming out with that trick. Next thing I tried was a screw extractor. Drill through the head, twist it in and out it should come. I happened to have a kit laying around...not sure for what since I rarely ever need on, but there it was. My first tip off should have been that one was missing. Well, now two are missing, with the other half of the one I tried tonight buried firmly in the bolt. Here's a little hint....don't buy cheap, Chinese extractors. Despite being absolute garbage, they are still hardened like taps and there is no way in the world you will ever drill it out. This severely limits your options, as option #3 is usually to drill the head off and then there are any number of ways to gently drive out the screw once the pressure is relieved. Now that's impossible because the extractor is in the way.
Here's the victim. You can see I've already started doing something to it. Documenting this was an after thought. Note the little dimple on the head to the left. That's a center punch.
247174
Now I drill a 3/32" hole through the side of the head. It's fairly important that you drill straight and don't wobble too much. Here's where having a good feel for drilling freehand can really turn an otherwise show stopping heading into no big deal.
247175
Why 3/32"? Well, this ain't my first rodeo and I just happen to have a broken 3/32" drill bit laying around for just such an occasion. On a larger bolt, use a larger bit. I often keep old bit around for things like this. I also use them as alignment pins...what better alignment pin to stick in a 1/4" hole than a 1/4" drill shank? :) I suggest you break or cut it off at the flutes as it WILL break there anyway and it's potentially very dangerous.
247176
Grab my spoke, give a little turn and presto. From major problem to minor inconvenience in just a few minutes.
247177
Now, you may only get a 1/4 turn. That's not enough, so you have to so this multiple times. If your drilling is sloppy, you will need to really slow down and concentrate or will run out of room very fast and have a hard time getting this to work. This particular one took three spoke holes until I could grab it with pliers and pull it out.
247178
Hope this helps someone when you have a difficult extraction to do with partially buried bolt head. :)