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A dicey repair

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Project by MatthewG posted 128 days ago 779 views 0 times favorited 9 comments Add to Favorites Watch

This is the second time around for this chair and me. I had restored a set of four ladderbacks, had the seats recaned, and have been enjoying them since. One of the chairs had two of the top rails fracture. The front rail broke across a short grain section (yes, I did think mean, mean thoughts about the guy who did not pitch that piece when building the chair originally) and the side rail had a classic stress fracture. (Could be someone stood on it, maybe.)

It took me a while and a bit of LJ browsing before I figured out how make the repair.

The two rails couldn’t be replaced without taking the whole chair apart, which was not at all attractive. So I turned matching red oak replacement rails—they are 1” diameter with 5/8” tenons on each end—making each rail about 3/4” longer than it would “need to be”—more on that later. The end tenons were cut with a tenon cutter on a drill press, after turning the table 90 degrees. (A better turner than I could have just sized them on the lathe…)

Once the rails were “done”, I cut a scarf joint across them—this is why they had to be longer than “they need to be”! The length is adjusted by jointing off the flats; try them, and remove material until they are the right length. A couple of screws to hold the scarf joints in line, some polyurethane glue, and the clamping went smoothly.

In the last picture, the front rail has been replaced, and the side one is in the clamps.

Here’s hoping that I don’t have to do this again!

Matthew

-- Matthew, from beautiful Wisconsin USA





9 comments so far

View woodchuckerNJ's profile

woodchuckerNJ

868 posts in 237 days


#1 posted 128 days ago

Too bad you used polyurethane glue.

Its the weakest glue there is. A better glue would have been yellow glue, and that’s the fact.
Screws should not have been necessary, you could wrap the joint with a rubber, like an old bicycle tube, or moving straps. You wrap it while pulling hard and it holds great.

I think you will be disappointed with the glue.

-- Jeff NJ

View MatthewG's profile

MatthewG

66 posts in 1382 days


#2 posted 128 days ago

Hi Jeff—

Do you had bad experiences with poly glues? I am always willing to learn. My experiences have been quite good, but it is not the glue for every application, that is for sure.

Over the last five years or so, there has been a lot of debate about the strength of glues. The strength of the glue is almost never (this is just my experience, and YMMV) the limiting factor. The direction of the load on the glue (shear vs. tension stress), the materials being glued (including the wood species), the quality of the surface (fresh cut vs. older stock), and the clamping force have a lot more to do with the strength of glued joints than the type of glue.

Most of the sources I see list polyurethane at about 3,000 psi, PVAs at about 3400 PSI, and the newer waterproof Titebonds at maybe 3700. So the difference is about 20%. The scarf joint has about six or seven square inches of surface area, giving about 10,000 lb strength even derating by half—this is not the part I need to worry about :)

I chose polyurethane since the tenons needed to be glued into holes that could not be completely cleaned out without damaging the joints. Polys are better at bonding to poor surfaces. Yellows, not so good. I am a great believer in testing, so I tried some simple test a long time ago when polyurethanes become commonly available. Now I use different glues for different purposes.

For the screws, they are for alignment and ease of assembly, not for strength. I would not trust screws as a clamp, nor would I use a rubber band or tube for a clamp. It can’t exert enough pressure on the joint to meet the glue manufacturer’s recommended clamping pressure.

Matthew

-- Matthew, from beautiful Wisconsin USA

View realcowtown_eric's profile

realcowtown_eric

288 posts in 540 days


#3 posted 128 days ago

And from my understanding, polyurethane glues are the only glue capable of bonding with other glues such as the residues left in the joints of chairs when repairing. If I’m wrong, please correct me.

The foaming capability also, at least in my pea brain, helps to fill the gaps.

If you have something that has been proven to be better for adhesion, anmising to glue remanants and gap filling I’d be only too happy to hear about it. particularly for chair repairs.

From concrete crack repair, you inject water into the cracks (much boring detail omitted) and inject the 2 part poly grout into the crack, and it has been described to me by my concrete cosultants as “following the water” and expaning to fill the gaps.

In this case, with that long scarf joint and mechanical fasteners, I wouldn’t worry about it, but as it’s clean wood, a PVA glue would be a slightly easier clean up. I really dislike the clean up of the overfoam of the polyurethane glues.

Eric

-- Real_cowtown_eric

View isotope's profile

isotope

18 posts in 227 days


#4 posted 128 days ago

I’m no expert, but my understanding is that the polyurethanes are good as long as there are no gaps in the joints. Otherwise, the resulting foam has low strength. There is an interesting article with test results on Woodgears.

View Oldtool's profile

Oldtool

1750 posts in 793 days


#5 posted 127 days ago

Nice repair on this chair, came out great. How did you cut the scarf joint on the rails?, table saw?
Thanks for showing, I learned another technique I may need someday.

-- "I am a firm believer in the people. If given the truth, they can be depended upon to meet any national crisis. The point is to bring them the real facts." - Abraham Lincoln

View gamygeezer's profile

gamygeezer

136 posts in 188 days


#6 posted 127 days ago

No comment on glues, but that is a nifty solution for replacing the broken rails.

Ken

-- What's a vibrant young guy like me doing in a broken down old body like this?

View Vertigo's profile

Vertigo

817 posts in 240 days


#7 posted 127 days ago

I agree no need to debate whether you like ford or Chevy better. It’s a great repair. That’s why I love this site. Lots of opportunity to learn from others experiences

-- Greg - Ferdinand and Son Construction: Do it right the first time. Like us on Facebook

View woodchuckerNJ's profile

woodchuckerNJ

868 posts in 237 days


#8 posted 127 days ago

So I have had bad results with Gorilla glue. I have stopped using the polyurethanes, preferring to use the yellow and epoxy. If it’s a gap that I need to fill, it’s done with epoxy. If I need a long working time, it’s white or epoxy 20 minute.
If it’s normal stuff, yellow, or white. The poly is so over hyped.

Also another good glue is the resinol (weldbond sells).

edit: So based on woodgears site, it seems that the tenons should have been glued with epoxy as the gorilla glue does not offer strength in loose joints from his tests.

I had bad results with outdoor repairs where the product should have excelled. They all failed quickly, even after tight bonds.

-- Jeff NJ

View MatthewG's profile

MatthewG

66 posts in 1382 days


#9 posted 127 days ago

Sorry to hear about you problems with poly glues. It would be worth while trying to figure out what went wrong. I have had good results myself, on a few different projects.

I googled “Weldbond”, and came up only with Weldbond white glue —which is a high solids PVA glue that gets good reviews. I might give it a try.

“Weldwood” sells multiple products, including a powder that is mixed with water. Is that what you meant? I might give that a try, too—never used it before.

I have used resorcinol to build a redwood play structure for my kids that stood up to 10 years of rain and snow. Remarkable stuff… it worked perfectly for that structure! I think “Resinol” is a medicated cream :)

And I will be sure to email you if the chair falls apart :)

Matthew

-- Matthew, from beautiful Wisconsin USA

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