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January 17, 2012

Saturday I decided to do some maintenance around the shop. I wanted to get my big top skin attached to my right wing, but my wife (and main riveter) had gone to St. Louis for a hockey tournament with my son. My daughter is getting better with a rivet gun, but I’m not quite comfortable letting her rivet a skin yet. So I decided to put my left wing skeleton on my wing stand and make sure there wasn’t anything that was going to need modification for the left wing. As it turned out my homemade bracket that holds the outboard rib to the wing stand needed trimming since it was going to interfere with the skins, so I broke out my die grinder and a 3″ cutoff wheel.

I’ve never had an incident with a die grinder but, the die grinder / cutoff wheel combo scares the fire out of me. Not as much as the drill press / fly cutter, but in the ballpark. For what I was doing, though, it was the right tool for the job. To prepare for the task I needed to assemble my safety gear. I went inside and put on another long sleeve shirt. I reached for my safety glasses but decided on the face shield instead I also put on my dust mask and hearing protection. At the last second I decided that my gloves couldn’t hurt either. Now I was set and ready for action. I was grinding away for about 30-seconds and it happened in an instant.


The cutoff wheel exploded sending shards all along the plane of travel of the wheel. Miraculously (or maybe it was physics) none of the pieces hit me. Small pieces did hit the leading edge of the right wing, my table and the ceiling of the garage. I disconnected the air and took stock of my appendages to make sure they were all there and look for shrapnel wounds. All clear. I picked up all the pieces of the failed wheel I could find and noticed that a large chunk was missing. I couldn’t find it anywhere. I assumed that it was traveling so fast that it tore a hole in the space time continuum and would erupt from a worm hole a million years in the future.

I replaced the wheel and got back to work finishing without incident. I got to thinking about my preparation. I am sure pieces hit my face shield. Had I put my safety glasses on instead I might be nursing some wounds on my face or forehead right now. My hands were really close to the action too. I don’t think anything hit them. I am very glad I took the 20-seconds to walk across the garage and get them and put them on.

What really scares me though, and the real lesson that I took away was the violence of the failed part and the force that the pieces had. If anyone else in the family had been in the garage with me there is a pretty good chance that they would have been standing in the path. I wouldn’t have thought twice about warning someone to get out of the way. It just wouldn’t have crossed my mind. I was also reminded that I am going to have to think about how my other tools might fail and what damage or injury they could cause. Am I taking the right precautions for the work I’m doing? I’ll have a safety stand down on Saturday and see what revelations come up.

Oh yeah. Remember that piece I couldn’t find? I found it today while I was on a conference call. I was speaking and saw this. I literally stopped in mid sentence. Everyone thought I my call had been dropped.

For scale, it was 8′ from the point of failure to the point of impact.

From what I can tell by the trajectory of this piece, it missed my wing by a fraction of an inch. Had my daughter been setting clecos in the wrong place, it would have hit her in the face or neck. Granted, this is a cheap interior door that it’s embedded in, but that thing would have left a scar in whatever it hit.

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