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Arggggh - please help me: fixing failed biscuit joint, pocket screws?

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Forum topic by Mark posted 04-28-2011 06:30 PM 6084 views 0 times favorited 17 replies Add to Favorites Watch
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Mark

26 posts in 3191 days


04-28-2011 06:30 PM

Topic tags/keywords: question cherry biscuit joiner joining

Arrggggh, guess this is one of those “learning days” for me in the woodshop. I could really use some advice to recover from my goof up.

So here I am building a blanket chest for my daughter, my first time using jatoba wood. The sides are basically rail and stile frames of 3” x 3/4” solid wood, using #20 biscuits and titebond 3 glue for the frame joints. The four sides were then assembled with glued T&G joints I had milled into the corner stiles. The panels, which will be upholstered (so my wife can contribute to the project since that’s her special skill), are not yet inserted. Here’s a photo:

Now for the dumb part (unless using biscuits for the frames was already dumb, making this the second dumb part): I set the chest up on four of those painting points so I could wipe on the finish right down to the bottoms of the legs. When I pushed too hard when wiping, one leg slipped off its painting point, dropping sharply a few inches onto the table. It was a hard knock at a racking angle and one of the biscuited joints popped open like this:

Inspecting more, I see the diagonally opposite joint has opened up too.

OK, I take a walk to let the frustration go and the varnish dry. Do I just reglue and reclamp? Or is the design bad – for example, maybe jatoba and biscuits don’t glue well. So I figured I can rescue this by installing pocket screws to reinforce the biscuited joints – after all, the cedar lining will hide them. But when I did an experimental biscuit + pocket screw joint on scrap, I found the pocket screws only end up chewing into the biscuit, which easily disintegrates. The screws don’t get a bite of the solid wood. Here’s a pic:

Now I’m stumped. So can anyone suggest what to do? Thanks in advance for any help you can give.
Mark

-- Mark


17 replies so far

View Loren's profile

Loren

8295 posts in 3108 days


#1 posted 04-28-2011 06:45 PM

You may not be using enough glue in the joints. That’s one thought.

I’d reglue and clamp. You can add reinforcement features when you
put the bottom in and so forth. A pocket-screwed stretcher perhaps
on the bottom – or just frame the bottom and screw it in on all four
sides.

View a1Jim's profile

a1Jim

115201 posts in 3037 days


#2 posted 04-28-2011 07:13 PM

Hi Mark
I have never used Jatoba but if it’s an oily wood you should clean all joints with acetone before gluing . As to your problem If you can get both sides apart the I would take it apart remove any old biscuits clean the joint and reglue. I would also check your glue and make sure it is not old . If you can’t get it apart safely then I would drill some small holes on the inside right were the crown of the biscuits are making sure not to go all the way threw and then pegging them . Of course you want it clamped tightly together before drilling. If you have doubts about the rest of the joints you can do the same with them. If you are going to do all the joints you might consider drilling from the outside and using a contrasting color wood for you peg as a design element.

-- http://artisticwoodstudio.com Custom furniture

View dbray45's profile

dbray45

3178 posts in 2236 days


#3 posted 04-28-2011 07:21 PM

I am making assumptions based upon what I have learned, if I am wrong, I apologize. Biscuits are for alignment only, structurally, they are not a good choice.

Giving the rails a tap with a deadblow hammer, use a cull between the rail and hammer to spread the load, see if the members are secure. If it comes loose, take it apart and clean. This is why I now mortise and tenon everything. Where the biscuits were, insert and glue replacement wood – fill the holes. Then redrill your pocket screws, align and these should hold. Biscuits are not strong enough wood to use as a filler. I would use pieces of the same wood that the rails and stiles are made.

If you don’t want to use the pocket screws, make loose tenons from the same wood and replace the biscuits, glue, and clamp for 24 hours. Apply enough glue, on both sides so that there is a small amount of sqeeze out. Remove this with a damp rag. The reason for putting glue on both sides – it works better, I use a roller to keep it smooth.

Feel free to modify as you wish, this has worked for me to repair failed joints. Good luck.

-- David in Damascus, MD

View a1Jim's profile

a1Jim

115201 posts in 3037 days


#4 posted 04-28-2011 07:30 PM

I agree with dbray in that loose tenons are stronger but I’ve used biscuits in the past and they have held up fine. Now days I mostly use loose tenons.

-- http://artisticwoodstudio.com Custom furniture

View Mark's profile

Mark

26 posts in 3191 days


#5 posted 04-28-2011 07:48 PM

Loren, Jim, David – thanks for the quick responses. These are great ideas for fixing this. I sure don’t want those joints to come apart years later when someone decides to use the chest as a stool or bench.

I see how I could plane down a piece of the jatoba and cut it into the right shapes to use as loose tenons, or as filler pieces so that pocket screws can bite. The effort of doing all that will drive a good lesson into me in why mortise and tenons have stood the test of time in this kind of joinery rather than the easy, modern biscuit. Thanks! And keep the ideas coming if there are more…

-- Mark

View Dennisgrosen's profile

Dennisgrosen

10850 posts in 2575 days


#6 posted 04-28-2011 07:53 PM

looose tennons now will be the right choice to make
next time real drawbored tennons :-)

Dennis

View reggiek's profile

reggiek

2240 posts in 2730 days


#7 posted 04-28-2011 07:58 PM

i agree with Jim….I switched from bisquits to loose tenons. I purchased a Domino as I am lazy and wanted a quick way to make the joints….but you can do the same thing using a drill press (or motiser) and cutting out your own loose tenon stock (I did this several times on projects before the Domino). Your best bet right now is to rebisquit and reglue.

I would not use pocket screws unless you have too….they would work perhaps but are really not good for a box that is going to be stressed alot – I use my pocket hole jig mostly for cabinet carcases and the like….wood will always part from screws and nails due to the internal stesses of the wood from moisture and drying…and from movement of the two woods together – Typically carcases have very little movement and/or unless you make sure that the stress forces are complimentary and do not spread the joint. I still glue pocket hole joints.

I have used jatoba in the past (also known as Brazilian Cherry though not a real cherry)....I have not had much problem glueing it but it is brittle (tearout is very bad on this wood) and will shear and crack easily….(pilot holes are required).....It is not recommended to use screws or nails in this wood. It finishes really well…and is not that oily….It has alot of stresses going on and will cup or warp easily iif not acclimated to your local humidity…..it will darken with age…which is a caution when staining.

Hope this helps.

-- Woodworking.....My small slice of heaven!

View a1Jim's profile

a1Jim

115201 posts in 3037 days


#8 posted 04-28-2011 08:04 PM

A couple strength test in finewoodworking I’ve seen actually rate loose tenons stronger the integral tenons because glue is stronger than wood.
Mark Don’t forget to check you glue and make sure it’s not out of date,because if it’s bad changing joinery won’t help.

-- http://artisticwoodstudio.com Custom furniture

View Bertha's profile

Bertha

13003 posts in 2153 days


#9 posted 04-28-2011 08:18 PM

I’m not a big fan of biscuits or loose tenons but I really have no reason other than stubbornness. I’ve used jatoba before and it is indeed very oily. I clamped a piece in my shop jack & oil actually oozed out. I like the idea of a quick acetone wipe. I might even try putting a heat gun to it (but that’s a difficult glue-up to sequence timely). Could you perhaps use a pocket screw with a bit more reach? I know you don’t want to risk busting through but from my cursory look, it looks like you’ve still got some meat. You could also try a very slender coarse Kreg screw. They seem to grab well for me when I resort to them.

Afterthought’s a drag but if you’re going to be building a lot of furniture like this (which is very nice, incidentally), a Domino or mortise/tenon jig might be a consideration. I’ve got the fancy tools but I still chop them by hand (cheaper than therapy). Good luck!

-- My dad and I built a 65 chev pick up.I killed trannys in that thing for some reason-Hog

View Mark's profile

Mark

26 posts in 3191 days


#10 posted 04-29-2011 01:55 AM

Thanks for the additional suggestions and thoughts. Here’s an update: I used a deadblow hammer to give a moderately hard knock to the joints. On the damaged frame, all four joints opened pretty easily; in all cases, the biscuit pulled cleanly out of the rail (i.e. the end grain component of the joint). Looking at the ends of the rails, there was very little glue residue in the biscuit slot, and no splintering.

Meanwhile, the biscuits remained fully intact and firmly glued in the stiles (i.e. the edge grain portion), My conclusion: the rail-to-biscuit joints were ‘dry’, and I think the combination of a porous biscuit absorbing the glue quickly, and the dense, hard end-grain surfaces of the jatoba (looks almost polished, actually) being slow to ‘wet’ with glue added up to cause the problem.

Originally I was going to completely remove the beechwood biscuits and make loose tenons out of the jatoba. But when I tried to dig one out it was bonded so well it was almost impossible to get out. And the biscuits seem to have plenty of tensile strength.

So based on this, I’m going to try re-gluing the rails onto the biscuits. But I will predrill the rails for pocket screws while they are out on the bench, just in case. I’m thinking polyurethane Gorilla glue won’t be as subject to the differential absorption problem. And I’ll swab the jatoba with acetone as Jim suggested. If the reglued joints show any signs of opening under stress, I’ll add pocket screws. Thanks to all of you. I’ll post the finished product, unless it ends up in the scrap bin.

-- Mark

View KnotWright's profile

KnotWright

252 posts in 2948 days


#11 posted 04-29-2011 02:34 AM

Mark, what type of glue are you using? Norm from the new yankee workshop talk about a few special types of glue for teak. I believe he prepped the joints with acetone prior to using the glue. I was trying to do a quick google search while I’m writing this but haven’t found the particular episode that this was discussed.

He has done a couple of different projects that addressed this problem and I believe he used different types of glue on each project. Guess that’s the advantage to having sponsors for your TV show.

-- James

View a1Jim's profile

a1Jim

115201 posts in 3037 days


#12 posted 04-29-2011 07:02 AM

Hey James
It was polyurethane glue same as gorilla glue but he used another brand I think Titebond. It was something not that well know back then . I believe it was the fancy teak garden bench he made .

-- http://artisticwoodstudio.com Custom furniture

View childress's profile

childress

841 posts in 3002 days


#13 posted 04-29-2011 07:30 AM

”Do I just reglue and reclamp?”

At this point, I would, but I would use epoxy….

-- Childress Woodworks

View dbray45's profile

dbray45

3178 posts in 2236 days


#14 posted 04-29-2011 02:08 PM

Another problem with bisciuts that I didn’t mention earlier is that there is not a high quality control. If the biscuits are too thin or when you cut the groove and have a heavy hand, your notches may be too wide. This would cause the joint to fail easily. It doesn’t take much. The adhesives rely on bonding to the wood, the the glue is thick, the joint will break.

-- David in Damascus, MD

View Bertha's profile

Bertha

13003 posts in 2153 days


#15 posted 04-29-2011 02:12 PM

^Dbray, that’s a pretty good argument for floating tenons. You control the quality if your shop-making. Good point.

-- My dad and I built a 65 chev pick up.I killed trannys in that thing for some reason-Hog

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