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biscuits for structural strength?

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Forum topic by JesseTutt posted 02-18-2013 at 07:44 PM 1045 views 0 times favorited 30 replies Add to Favorites Watch
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JesseTutt

803 posts in 748 days


02-18-2013 at 07:44 PM

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

1271 posts in 1007 days


#1 posted 02-18-2013 at 07:47 PM

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.

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ClayandNancy

479 posts in 1652 days


#2 posted 02-18-2013 at 07:57 PM

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

7464 posts in 2285 days


#3 posted 02-18-2013 at 08:00 PM

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.

-- http://lawoodworking.com

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404 - Not Found

2544 posts in 1606 days


#4 posted 02-18-2013 at 08:13 PM

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

1433 posts in 998 days


#5 posted 02-18-2013 at 08:40 PM

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

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

View a1Jim's profile

a1Jim

112030 posts in 2214 days


#6 posted 02-18-2013 at 08:50 PM

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

2163 posts in 1487 days


#7 posted 02-18-2013 at 09:12 PM

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"

View JesseTutt's profile

JesseTutt

803 posts in 748 days


#8 posted 02-18-2013 at 09:14 PM

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 1606 days


#9 posted 02-18-2013 at 09:56 PM

^ It depends…

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404 - Not Found

2544 posts in 1606 days


#10 posted 02-18-2013 at 10:03 PM

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

View TimberFramerBob's profile

TimberFramerBob

68 posts in 560 days


#11 posted 02-18-2013 at 10:03 PM

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

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

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pintodeluxe

3337 posts in 1450 days


#12 posted 02-18-2013 at 10:04 PM

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

13873 posts in 975 days


#13 posted 02-18-2013 at 10:12 PM

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

6928 posts in 1551 days


#14 posted 02-18-2013 at 10:15 PM

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

684 posts in 1572 days


#15 posted 02-18-2013 at 10:26 PM

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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