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Strength of different joints?

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Forum topic by lightning33 posted 01-21-2019 02:37 PM 990 views 0 times favorited 12 replies Add to Favorites Watch
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lightning33

12 posts in 856 days


01-21-2019 02:37 PM

I have no idea how to even begin to think about the strength of thr various joints? For example, I am planning a farmhouse table. What joinery options would be strong enough to hold someone leaning on the breadboard end? All of them?

Is there some sort of reference chart?

Thanks!


12 replies so far

View HokieKen's profile

HokieKen

17541 posts in 2217 days


#1 posted 01-21-2019 02:58 PM

It depends on lots of things. First is the wood. Hickory will hold a lot more weight than Pine. Some joints rely on surface area of long grain for strength. By increasing surface area, you increase the glue bonding strength. For a breadboard end, most often a mortise and tenon joint is used and pinned in a couple of spots. You generally wouldn’t glue this joint because it needs to be loose to allow the table top expansion and contraction to occur independently of the breadboard. If you’re intending the breadboard to carry much load (such as someone sitting on it) you would want to use a larger and deeper tenon than is typically used I think.

All this is just broad strokes though. If you’re looking for specific recommendations, a picture and some details about your project and the materials will get you better advice.

-- I collect hobbies. There is no sense in limiting yourself (Don W) - - - - - - - - Kenny in SW VA

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Robert

4553 posts in 2559 days


#2 posted 01-21-2019 03:27 PM

A rule of thumb is to make the tenon depth 2/3 the width of the breadboard.

So making the tenons too short is a common mistake. Another mistake is making them too wide, which increases the risk of cracking when big ole 300# Uncle Buck leans on it. Also the risk of cupping.

As Kenny said, a lot depends on the wood but also the grain. Softer woods and very straight grain will be more subject to cracking under weight.

With a farmhouse table, the top should be pretty thick, so I don’t think you’ll have much to worry about.

-- Everything is a prototype thats why its one of a kind!!

View Sludgeguy's profile

Sludgeguy

59 posts in 1201 days


#3 posted 01-21-2019 03:36 PM

If it’s thick enough a hardwood spline or two with a good glue-up seems like it would be fine

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bilyo

1363 posts in 2181 days


#4 posted 01-21-2019 10:55 PM

Aside from the breadboard question, I think it was Fine Woodworking that did an article on the strength of various joints; sometime within the last 4-5 years I think. You could probably fine similar information with a google search.

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NewShop

3 posts in 840 days


#5 posted 01-21-2019 11:57 PM

I have the same question….............strength of the various joints? + Is there some sort of reference chart?

Lightning wrote for example a farm house table so I figure he along with myself and many others wants to build a multiple of things that strength in the joints are essential. Not knowing which joinery works best for different projects like a workbench, assembly table, tool carts, shop storage and counters etc makes it hard for me to start a project.

I was not able to find a “chart” online but maybe some of you experienced woodworkers could let us know your top 3 choices for strength and if there are any joints to just stay away from using.

Thanks,

John

-- John

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Woodknack

13557 posts in 3458 days


#6 posted 01-22-2019 02:06 AM

Tage Frid wrote a trilogy that will answer these questions and many more you didn’t know to ask.

-- Rick M, http://thewoodknack.blogspot.com/

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Phil32

1387 posts in 982 days


#7 posted 01-22-2019 02:19 AM

Many joints are stronger than the wood they connect. That is, the wood will often fail before the actual joint. As stated above the strength increases with the surface area of the glued wood.

-- Phil Allin - There are woodworkers and people who collect woodworking tools. The woodworkers have a chair to sit on that they made.

View rcs47's profile

rcs47

225 posts in 4208 days


#8 posted 01-22-2019 02:30 AM

Fine Woodworking issue #203 (Jan/Feb 2009) tested different joint types to failure. I remember they had a table with strengths for different joints, but my copy is long gone.

This takes you to the FWW page on the table, but you will need to sign up for their service to see the data:

https://www.finewoodworking.com/2009/01/01/joinery-shootout

-- Doug - As my Dad taught me, you're not a cabinet maker until you can hide your mistakes.

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NewShop

3 posts in 840 days


#9 posted 01-24-2019 03:18 AM

Thanks for the info, good reading. I have the tendency to want to over build. I plan on making an assembly table/work bench maybe with built-in router table. One of the things I can’t figure out reading and watching videos is people make these large sturdy legs and base then screw in levelers to the side of legs. Makes me think that I dont need so much heft in my plans and spend more time making sure everything straight, square and true or I have to find a better way to use leveling legs.

-- John

View jonah's profile

jonah

2136 posts in 4377 days


#10 posted 01-24-2019 05:25 PM

IIRC, bridle and half lap joints were the strongest, followed by mortise and tenon joints and then others. With modern glues, basically every kind of glue joint is stronger than the underlying wood – the wood around the joint will fail before the joint does. Even miter joints didn’t fail at the glue line.

View BalsaWood's profile

BalsaWood

179 posts in 2237 days


#11 posted 02-15-2019 10:06 AM

There are many different joints you can use- some much harder to do than others. The mortise and tenon joint is nice and simple. Loose tenon and dowels (as long as you use a few per joint) are also good options that are simple- the main thing is that modern glues are very strong as others have mentioned. Getting stuff straight and square first would be the most important thing since it makes the joinery much easier.

I also wouldn’t overthink the strength of many of those types of joinery. Unless you are going to be jumping around on it or driving a car over the furniture, it should be fine and last a long time.

View Brawler's profile

Brawler

206 posts in 909 days


#12 posted 02-15-2019 12:33 PM

There is a book with charts on joints called “Good Wood Joints”. You can get a “free” PDF online. Just google the book title and you will see it in images, hope this helps.

-- Daniel, Pontiac, MI

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