# biscuits for structural strength?



## JesseTutt (Aug 15, 2012)

Are woodworking biscuits intended for alignment purposes only or do they add structural strength to the joint? I have read both stories on the Internet.


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## BinghamtonEd (Nov 30, 2011)

I would be interested to see an actual data comparison, if anyone has one. I used to use biscuits for alignment. From what I concluded, biscuits in a long-grain to long-grain joint did not add any structural integrity, as long-grain to long-grain is going to be as strong as it gets. In situations involving end-grain, such as butt joints and miter joints, they did offer some strength.

But again, I'd like to see real data.


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## ClayandNancy (Feb 22, 2010)

My only reason for using biscuits is for alignment, I don't believe they are really adding any strength to the joint, but I could be wrong.


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## Loren (May 30, 2008)

In long glue joints they don't add much but they can
help with aligning boards if you don't have other 
methods like cauls to do it.

Sometimes I have put little wire nails in the edge of
a board and clipped the heads off. As the clamps
are closed, the clipped off nails are pressed into
the other board and the boards won't slip around.

Don't try to glue end grain to end grain or end
grain to long grain without putting a reinforcement
of some kind. Biscuits work, as do dowels, nails, 
screws, tenons, and so forth.


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## renners (Apr 9, 2010)

Are biscuits for alignment or do they add strength?

You will find the camp divided on this question. I personally say they add strength, and base this on the fact that when I've tried busting apart a piece that was biscuit jointed it has been a lot harder than a similar piece that wasn't.


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## ClintSearl (Dec 8, 2011)

Alignment only; I don't glue them in. Never had a joint fail.


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## a1Jim (Aug 9, 2008)

I agree that on long joints there are not necessary for strength, I've not found of using them at all for long grain and rarely for other joinery. Yes biscuits do add strength to other types of joinery like butt joints but if you really need a strong joint I would prefer other types of joinery rather than biscuits .


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## LeeBarker (Aug 6, 2010)

Ok. We're clear on the long grain to long grain issue.

As for end grain to anything else, it would depend on the joint and the stresses it will likely undergo. In general, a mortise and tenon joint with 95% glue failure will still withstand shear if there are no forces trying to remove the mortise from the tenon.

Further, if there is potential for racking, I'd put my coins on the MT.

That said, there are many applications where a biscuit joint is just the ticket, and blindingly fast.

Short answer? "It depends." The more joints you have in your skillset, the better the project will proceed.

Kindly,

Lee


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## JesseTutt (Aug 15, 2012)

Thanks all!

I went ahead and glued three biscuits into the 33 inch long board.


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## renners (Apr 9, 2010)

^ It depends…


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## renners (Apr 9, 2010)

If it's going in a glass case and will only ever be touched by someone wearing white cotton gloves, and handled like a Faberge Egg, then biscuits would probably suffice. Just my 0.02


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## TimberFramerBob (Feb 18, 2013)

LOL…..im a big fan of mortise and tenon.


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## pintodeluxe (Sep 12, 2010)

Biscuits add considerable strength to a glueup. In endgrain-to-long grain joints, the glue itself has very little strength. In these applications biscuits are structural. They are great for web frames in case goods. 
Tabletops probably don't need biscuits most of the time, but they are added security.

If anyone doubts the strength of a biscuit, just join two small boards without glue. Then soak them in the sink for a few minutes. I did this, and passed the boards around to see if anyone could pull the boards apart. Nobody could! 
Some brands are better than others, I like the Dewalt biscuits (they fit better).


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## mojapitt (Dec 31, 2011)

I use them. At least in my mind it's a stronger joint.


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## HorizontalMike (Jun 3, 2010)

Jesse: "...I went ahead and glued three biscuits into the 33 inch long board…."

Jesse, I just completed a Shaker chest that had 5ft tall legs that called for biscuits to join them to 3/4in veneer ply sides, however, not having a biscuit joiner, I chose to use a long dado to join these legs to the sides. See upper left, where leg is dado'd. Worked great and added strength. Many ways to do this…

http://lumberjocks.com/projects/78752


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## ChuckC (May 13, 2010)

Alignment for me. It may add a little strength but if I'm concerned about strength for a particular joint I'll go with something other than a biscuit.

I Liked the clipped nail idea Loren mentioned!


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## shawnmasterson (Jan 24, 2013)

#1 I thought biscuits were laminated like ply wood


> ?


#2 they serve a similar purpose to a spline type joint so how could they not add strength


> ?


some one please educate me cause they seem to be a faster version of a spline joint to me.


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## unisaw (Jan 31, 2007)

I built a TV stand based on plans from FWW:

http://www.finewoodworking.com/woodworking-plans/article/a-low-console-for-home-theater.aspx

The plans called for dry biscuits and screws - NO GLUE. I cannot for the lfe of me figure how this would survive with no glue! The move alone from the shop to the family room of this 100 lb beast (in two pieces) would be impossible. Mind you - my biscuit joiner is a sloppy-blade ryobi. Even with a tight fit - I just don'e understand how dry biscuits do more than align.


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## a1Jim (Aug 9, 2008)

Biscuits are compressed not laminated . Once the glue hits them they expand.
I have student bring me plans of thing they want to build that the measurements,joinery and finish projects are terrible. 
Biscuits with out glue is a good example of how off base they can be.

Edit 
after following your link the biscuits may just be for alignment and there are screws to take the place of glue.
I did not see the plans so this is just a guess. Unless your building what's callled knock down furniture I would all ways use glue on joinery that's meant to stay together.


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## unisaw (Jan 31, 2007)

IF you look at the plans, there is just no way that screws would give the support needed to keep the piece from racking.


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## bondogaposis (Dec 18, 2011)

It depends on what kind of joint. They are stronger than a butt joint but not nearly as strong as a mortise and tenon would be in the same situation. For edge joints, they are just an alignment tool.


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## TCCcabinetmaker (Dec 14, 2011)

Ok, here's why they do increase strength, they increase the surface area being glued. I've used them in slab doors to increase the strength of the door so that it would not be easly snapped on the long grain joints. Mostly though they are used for alignment.


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## MrRon (Jul 9, 2009)

I really wouldn't depend on biscuits for perfect alignment. There is always just enough slop in the biscuit and slot to prevent perfect alignment; at least, I have never been able to get it. When running my finger tip across the dried joint; I can always detect a slight difference. In an end grain application, they will add some strength to the joint (assuming a butt joint), but not much; only enough to keep the joint together. I would never depend on biscuits alone for strength.


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## renners (Apr 9, 2010)

MrRon, I started off with a Chinese biscuit jointer. It was terrible. Cut slots all over the place and the boards would never line up. Traded up to a DeWalt and it is perfect every time. Lesson learnt.


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## Kazooman (Jan 20, 2013)

I agree that they don't add much if anything to a long-grain to long-grain joint other than alignment. I don't bother to use them there. I do believe that they add strength to the miter joints such as in a frame and panel door or chest top. I always use them there and I do apply glue.

There. Now you have all possible opinions, just like you found in your internet search!

One potential problem I have heard about with biscuits, but have never personally observed, is from the swelling. With soft woods, if the biscuit is too close to the surface the swelling from moisture in the glue can push up the surface. You don't realize this and go ahead and sand the piece flat for finishing. In time things shrink back and you end up with depressions where the biscuits are.

Here's a reference:

http://www.highlandwoodworking.com/whenbiscuitjointsgobad.aspx

They say that you can avoid the problem by NOT using glue on the biscuits!


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## AlaskaGuy (Jan 29, 2012)

http://en.wikipedia.org/wiki/Biscuit_joiner


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## MrRon (Jul 9, 2009)

Renners; I found that biscuits from different suppliers are not all the same. Some are a tight fit and some are a loose fit. I have a PC biscuit joiner and can never get a perfect fit. 1 out of maybe 5 tries will be a good fit. I always end up having to sand the surface flat to get rid of the height difference. My preference for any butt joint is the spline method. Run a dado through along the fence, turn wood around and run through the saw again. This will give you a perfectly matched dado in each piece. Cut a spline and fit it.


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## TCCcabinetmaker (Dec 14, 2011)

MrRon, the old style Porter Cable biscuit jointers always gave me fits when I went to use them, they are back heavy which makes them hard to keep square. I found a freud marked down for like 50 bucks in a lowes, bought it and haven't had many issues since, other than they put a piece of plastic right down the middle of the dust outflow… always jams but not really a bad thing to work around.

I will ask this question though for those that don't think biscuits add strength. Do splines add strength to a joint? Does a tounge and groove add strength to the joint? This is the same concept, increased glueing surface.

Oh, and P.s Porter cable makes their own brand of biscuits to.


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## wormil (Nov 19, 2011)

Biscuits are like little tenons or splines and are useful in the same applications.


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## oldnovice (Mar 7, 2009)

Yummy biscuits


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## Surfside (Jun 13, 2012)

Smaller biscuits work well for strengthening corner joints.


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