Engineering Solutions for a Broken Chair

[Lancelot59]

I guess this goes under engineering, but if not then whoops.

I sat down hard on a wooden chair recently and heard a loud snap noise. I discovered that the wooden pegs that connected the right seat support to one of the back legs had snapped. So I pulled the chair apart and drilled out the remains of the pegs.

My idea being that I could just drill the holes in the back leg all the way through and put some long screws into re-attach the pieces. The problem is when I checked the diameter of the pegs to select a bit to remove them I measured the middle instead of the base, and they were made of a soft material that compressed to fit the hole in the support, so the holes are a little wide now.

I drilled them out with a 3/8 inch bit. I just went to the hardware store and the only thing they had that was big enough to work were 1/2 inch lag bolts. I would need to get some nice fat four inch long ones to do the job.

Using this plan I would widen the holes in the support/leg to be wide enough to accept the shaft of the bolt, and let the threads dig in on their own. Then after countersinking the holes in the back leg put everything back together.

Does this sound like a reasonable solution?

 

[AlephZero]

Why not get some wood dowel unstead of metal bolts?

It doesn't matter if you use a bigger size dowel than the original, and you can drill right through the leg if you don't care what the repair looks like.

You want dowel that is grooved along its length (like a rifle barrel, but straight grooves not sprirals) so it can be compressed into a slightly undersized hole, and the grooves hold plenty of glue while it is being assembled.

If you think glue will not be strong enough on its own, you can put a small nail through the leg and the dowel at right angles to the dowel, to stop the joint pulling apart.

 

[DaveC426913]

Using this plan I would widen the holes in the support/leg to be wide enough to accept the shaft of the bolt, and let the threads dig in on their own.

If the holes were large enough to let the threaded bolt through, it sounds like there'd be some gap and they might not grip. You might dip the bolt in white glue before putting it in.

 

[Lancelot59]

Why not get some wood dowel unstead of metal bolts?

It doesn't matter if you use a bigger size dowel than the original, and you can drill right through the leg if you don't care what the repair looks like.

You want dowel that is grooved along its length (like a rifle barrel, but straight grooves not sprirals) so it can be compressed into a slightly undersized hole, and the grooves hold plenty of glue while it is being assembled.

If you think glue will not be strong enough on its own, you can put a small nail through the leg and the dowel at right angles to the dowel, to stop the joint pulling apart.

Well I do want it to look alright. I'm reluctant to use dowel, I'm concerned it will just break if I fall into the chair again.

If the holes were large enough to let the threaded bolt through, it sounds like there'd be some gap and they might not grip. You might dip the bolt in white glue before putting it in.

I meant to say that I would only provide clearance for the shaft. The threads would still be able to dig in.

 

[DaveC426913]

I meant to say that I would only provide clearance for the shaft. The threads would still be able to dig in.

You may have a heckuva time screwing that bolt into wood.

 

[Lancelot59]

You may have a heckuva time screwing that bolt into wood.

That's why we invented power tools? I didn't see any actual screws that were a half inch wide at the store, and I don't really think dowels are the best option, although I may just do that. I guess I could always sentence the wood to the scrap pile and make one from scratch, but I don't want to unless I need to.