Steel pin chair repair (horizontal boring machine to the rescue)
The problem with this chair is that the legs are turned down too thin, creating a weak spot. Even if I fixed it good as new, it still wouldn't be very good. Initially I promised only to try gluing it back together, but then I had an idea for reinforcing it with a steel pin.
I needed to drill a hole exactly down the middle of both parts to get sufficient alignment for a steel pin. I figured the best way to get this was to make a jig out of wood. I first drilled a hole that would fit over the broken part, then another hole in the middle to guide a the drill for drilling a hole in the middle of the leg.
The only way I could save this now was to drill the hole with the same offset in the bottom of the chair seat. But I couldn't count on using my jig to line that up accurately enough.
I don't use the horizontal boring machine very much. In part because setting stuff up on it takes longer than using a drill press, but also because it's a type of machine few people have. I can't encourage you to build one because this one relies on parts that I have no idea where they could be bought. It uses an old X-Y mill/drill table and a bearing block/drill chuck assembly. The table came from a surplus sale, the bearing block was given to me.
I cut the right length from a 12 mm shaft, that came from this printer. It was the feed roller, with a rough texture to engage the paper, so I couldn't use it for building machines anyway.
I couldn't get the leg on with the pin as well as I could without it. On careful examination, I realized the hole alignment may have been off by a fraction of a millimeter.
So I clamped the chair back on the machine, adjusted the drill position, then slowly drilled again. There was some flexing of the drill bit so I had to overcompensate for the offset, but I managed to get the hole expanded enough get it into alignment.
Back in my basement shop, I glued it back together. I used some PL premium construction adhesive. It says it bonds metal, and it's a good gap filler (the rod didn't fit as tight as a dowel), so I figured it was a good glue for the job.
I made sure I had enough glue smeared on to fill the gap, but it turned out to be too much glue. The pin acted like a piston, preventing me from getting the leg all the way on. But slowly forcing it down with a clamp allowed the glue to squeeze past the pin. I guess this, and the alignment, would have been much easier if I had drilled the holes half a millimeter larger.
Fortunately, the glue cleaned up well with a rag.
If you look closely at the leg, you can clearly see where it's joined, and it may be half a millimeter longer than it was before. But with the steel pin, that leg should definitely be stronger than it was originally.
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