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biscuits for structural strength?

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Forum topic by JesseTutt posted 423 days ago 934 views 0 times favorited 30 replies Add to Favorites Watch
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JesseTutt

763 posts in 610 days


423 days ago

Topic tags/keywords: question biscuits adding structual strength to a joint

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.

-- Jesse, Saint Louis, Missouri


30 replies so far

View BinghamtonEd's profile

BinghamtonEd

1000 posts in 869 days


#1 posted 423 days ago

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.

-- - The mightiest oak in the forest is just a little nut that held its ground.

View ClayandNancy's profile

ClayandNancy

478 posts in 1515 days


#2 posted 423 days ago

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

6746 posts in 2147 days


#3 posted 423 days ago

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.

View 404 - Not Found's profile

404 - Not Found

2544 posts in 1469 days


#4 posted 423 days ago

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.

View Clint Searl's profile

Clint Searl

1318 posts in 861 days


#5 posted 423 days ago

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

-- Clint Searl.............We deserve what we tolerate

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a1Jim

109242 posts in 2077 days


#6 posted 423 days ago

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 .

-- http://artisticwoodstudio.com Custom furniture

View Lee Barker's profile

Lee Barker

2159 posts in 1350 days


#7 posted 423 days ago

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

-- "...in his brain, which is as dry as the remainder biscuit after a voyage, he hath strange places cramm'd with observation, the which he vents in mangled forms." --Shakespeare, "As You Like It"

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JesseTutt

763 posts in 610 days


#8 posted 423 days ago

Thanks all!

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

-- Jesse, Saint Louis, Missouri

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404 - Not Found

2544 posts in 1469 days


#9 posted 423 days ago

^ It depends…

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404 - Not Found

2544 posts in 1469 days


#10 posted 423 days ago

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

68 posts in 423 days


#11 posted 423 days ago

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

-- ..........a man who works with his hands, his brains, and his heart.....is an artist.

View pintodeluxe's profile

pintodeluxe

3025 posts in 1313 days


#12 posted 423 days ago

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).

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View Monte Pittman's profile

Monte Pittman

10778 posts in 838 days


#13 posted 423 days ago

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

-- Mother Nature created it, I just assemble it. - It's not ability that we often lack, but the patience to use our ability

View HorizontalMike's profile

HorizontalMike

6689 posts in 1413 days


#14 posted 423 days ago

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

-- HorizontalMike -- "Woodpeckers understand..."

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ChuckC

673 posts in 1435 days


#15 posted 423 days ago

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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