# Box joint failure



## danridout (Jan 5, 2019)

Long time lurker here, first time poster, had a question I'm hoping some of the folks here can help with.

I made this fairly simple bookcase for a client. The only real joinery is box joints attaching the top to the sides of the case. I'm not the greatest woodworker so this joint was certainly not perfect. You can see some small gaps between some of the fingers. But overall the joint fit snugly, most of it had no visible gaps and was glued with Titebond.










After shipping, the customer sent me this picture which clearly shows joint failure. This joint is 12 inches long, the case is constructed from hard maple.










I may be showing my lack of experience here, but I'm somewhat baffled as to how this could happen. The customer said the packaging showed no damage, so I would assume it didn't sustain some heavy blow during shipping. Only thing I can think is the joint was glue starved, but that seems unlikely. There is no cross grain in this piece so I would not expect wood movement to be the culprit.

I'm scratching my head trying to figure out what the build failure is here. Any thoughts?


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## wapakfred (Jul 29, 2011)

Looks to me like the board that moved probably cupped some, though I wouldn't have thought it would separate in the joint like that. So to me it may have been the joint didn't have quite enough glue (or fit may have been too loose in that corner. But this is all guesswork.


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## MrRon (Jul 9, 2009)

If the bookcase is tall without FIXED shelving, it would be subject to racking and if the joint were glue starved, that could cause the joint to open up. With fixed shelves, racking would not be such a problem. This is just an assumption since I don't have the entire bookcase and dimensions to look at. Also is there a back on the bookcase? A back will prevent racking.

Unless you want to take it back and fix it (at your expense), I would just offer to rebate say 50% of the cost and hope he will accept that.


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## dbw (Dec 2, 2013)

Either the fingers are glue starved and/or the gaps are too big for the glue to work correctly. Did this happen on ALL the joints or just the one in the picture?


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## danridout (Jan 5, 2019)

Thanks for the replies. This one joint is the only one that separated according to the customer, I'm not able to inspect it at the moment.



> If the bookcase is tall without FIXED shelving, it would be subject to racking and if the joint were glue starved, that could cause the joint to open up. With fixed shelves, racking would not be such a problem. This is just an assumption since I don t have the entire bookcase and dimensions to look at. Also is there a back on the bookcase? A back will prevent racking.
> 
> Unless you want to take it back and fix it (at your expense), I would just offer to rebate say 50% of the cost and hope he will accept that.
> 
> - MrRon


Here's the whole piece. I don't know why I can't get it to post properly oriented, sorry about that.










It's fairly simple, fixed shelves sit in dados, glued only in the center. It has a partial back at each shelf. That was as a design element, to prevent anything from being pushed through and out the back, and to provide some rigidity. I was a little concerned about racking without a full back, but honestly I tested it and between the fixed shelves, the partial back and the rigidity of the joints themselves, it seemed awfully sturdy. I think I'm just chalking it up to glue starvation at this point. And probably a strong racking force, but that's just speculation.


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## bilyo (May 20, 2015)

Blowing up your picture, it doesn't look like you had any severe gaps where it failed. I too think it must be glue starvation. It is possible when putting together these types of joints that the glue can get rubbed out as they slide together; particularly if they are a bit to tight and have to be persuaded.

My method of gluing, which not everyone agrees with, is to make sure I have coated both surfaces with glue before assembly. This takes a bit more time, but it assures that both mating surfaces are wet with glue and helps to prevent a starved joint.


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## pottz (Sep 15, 2015)

> Blowing up your picture, it doesn t look like you had any severe gaps where it failed. I too think it must be glue starvation. It is possible when putting together these types of joints that the glue can get rubbed out as they slide together; particularly if they are a bit to tight and have to be persuaded.
> 
> My method of gluing, which not everyone agrees with, is to make sure I have coated both surfaces with glue before assembly. This takes a bit more time, but it assures that both mating surfaces are wet with glue and helps to prevent a starved joint.
> 
> - bilyo


+1


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## ChefHDAN (Aug 7, 2010)

I'm thinking maybe it was the open time of the glue, which Titebond did you use? TBIII (green) has about 8 minutes of open time before it will begin to skin over, and the TBI only has about 5 minutes. See TB Specs here

Since it was only the one joint it could also be how you went about your glue up, if this was the first joint you applied glue to and your open time closed before all of the joints were coated with glue and you got clamped up, the glue may have skinned over and never bonded well in the first place.


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## splintergroup (Jan 20, 2015)

I'd vote for glue starvation (not enough or skinned over before clamping).
Even small boxes with box joints give me grief when gluing since one must work fast to get the glue applied and clamped within a few minutes. Many glues have long working times (i.e. resorcinol) which would be much more forgiving.

After assembly you can reinforce the joint by driving in a pin (1" long x 1/4" dowel would work) on each corner, front and back, to lock the corners into place.


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