coffee table build - Woodworking Talk - Woodworkers Forum
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post #1 of 19 Old 04-01-2018, 08:45 PM Thread Starter
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coffee table build

Ok I want to build this coffee table, 18" wide, 28" long and 17 or 18" high. The top will be 2" thick walnut. Instead of using metal legs, I would like to use 4/4 walnut and assemble them with dovetails. My only question is what would be the best way to attach the square legs to the top besides using lagbolts ? Any ideas ? Do you think this table will be solid enough using lagbolts or should I just scratch the square legs idea and go with something else ?
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post #2 of 19 Old 04-01-2018, 09:01 PM
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I would want some diagonal supports or at least a stretcher of some sort.

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post #3 of 19 Old 04-02-2018, 12:13 AM
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Quote:
Originally Posted by charlo489 View Post
Ok I want to build this coffee table, 18" wide, 28" long and 17 or 18" high. The top will be 2" thick walnut. Instead of using metal legs, I would like to use 4/4 walnut and assemble them with dovetails. My only question is what would be the best way to attach the square legs to the top besides using lagbolts ? Any ideas ? Do you think this table will be solid enough using lagbolts or should I just scratch the square legs idea and go with something else ?
Hi Charlo,

I like the simple lines of this type of design which is very popular now in the minimalist modern trends...

There are all joinery methods for such a table as this...like sliding dovetail and related. It will need some strengthening up under the table as Difalkner rightfully suggested otherwise it could end up a wee bit wobbly...

This has a lot of hand tool work...

Are you interested and/or up for that?

Again nice design!

j
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post #4 of 19 Old 04-02-2018, 02:00 AM
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joining dissimilar elements ....

When joining/attaching elements that are in different planes, especially at 90 degrees, the strength is either in the joint or the means of attachment..... HUH?

Joints can be structural in themselves, like mortise and tenon, half laps, or dovetails. If you don't make the joint itself structural, the strength comes only from the screws or glue holding it together ... not good.

A butt joint, especially involving end grain to either end grain or long grain relies on the glue bond which is the weakest type. Long grain to long grain is the strongest bond glue will have.

As far as your table design goes, the 90 degree joints in the frame corners will not withstand any lateral forces, like a push from the side or end, IF miters or butt joints are used. Typically, that design is made by laminating thin layers over a form with radiused corners providing great structural strength. Then the issue of attaching the flat top bar to the bottom of the top becomes primary. Screws up through the bar would be typical. A recess for the bar to sit in, a shallow mortise, would add strength.

To make that type of table that will endure the rigors of time requires a thoughtful analysis of the forces and the methods of joinery. Glue is simply not sufficient. Similar table have been nailed and glued or screwed together, but they will not last. Typically, these days a welded steel frame is used, not wood and that provides the strength required.
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post #5 of 19 Old 04-02-2018, 08:23 AM Thread Starter
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Yeah I taught about the sliding dovetail thing to attach the legs to the top but it seems so hard to do such a huge joint !

And woodnthings, I don't plan on butt joints to assemble my legs, I will use dovetails and glue for all of them. Would that be strong enough to resist a side push on the table ? I think so, it's a coffee table, it won't be abused much like a diner table. Otherwise, I agree that bended steel legs might be stronger
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post #6 of 19 Old 04-02-2018, 08:38 AM
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With that design I think I would be inclined to make the legs out of tubular steel and veneer over it. Even with diagonal bracing it would also need bracing lengthwise too. That would completely change the design. Steel would do it. You could make some elongated holes in the top of the legs and just screw it to the top. Covered with veneer the legs would take the appearance of wood so nobody would be the wiser.
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post #7 of 19 Old 04-02-2018, 08:46 AM
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Here comes the monkey wrench - have you thought about wood movement? If I were building that table, I would recess the legs into a mortise like woodnthings suggests and I would only glue the center 1/4 of the total width. That top will move a good 3/16 of an inch over the course of a year.

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post #8 of 19 Old 04-02-2018, 11:03 AM
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The reality is .....

Quote:
Originally Posted by charlo489 View Post
Yeah I taught about the sliding dovetail thing to attach the legs to the top but it seems so hard to do such a huge joint !

And woodnthings, I don't plan on butt joints to assemble my legs, I will use dovetails and glue for all of them. Would that be strong enough to resist a side push on the table ? I think so, it's a coffee table, it won't be abused much like a diner table. Otherwise, I agree that bended steel legs might be stronger
Have you ever sat on coffee table? Have children ever stood on a coffee table? The dovetails may be just fine, but it would be a shame to do all that work and have a failure. Make a few test samples and test them, that way you'll know for sure.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #9 of 19 Old 04-02-2018, 11:29 AM
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Quote:
Originally Posted by charlo489 View Post
Yeah I taught about the sliding dovetail thing to attach the legs to the top but it seems so hard to do such a huge joint ...

I don't plan on butt joints to assemble my legs, I will use dovetails and glue for all of them. Would that be strong enough to resist a side push on the table ?

I think so, it's a coffee table, it won't be abused much like a diner table.

Otherwise, I agree that bended steel legs might be stronger
Hello Charlo,

Steve's (et al) observation about steel legs of your current design will be strong, and if you weld (or know someone that does) it will be perhaps the easiest to facilitate...Attachment will most likely be with hardware, though there are strap and wedge methods to attachment as well.... It will change the overall design and feel of the piece.

I also agree, as you have suggested and thought about this... if its just a coffee table meant for lite loads and not the center piece for something like a game room where folks are resting their feet on it...it should be more than strong enough...even without glue...if the correct joinery is employ and executed properly...

Butt Joinery of certain types can be used...again...if laid out and facilitated properly...

Sliding dovetails are not as difficult to cut as you may think. I use them in green wood all the time for certain applications where I need a large slab to be strengthened from underneath so the wood can move during drying and with seasonal changes in humidity...

Here are a few video of quality that may be of service?


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post #10 of 19 Old 04-02-2018, 11:32 AM
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The entire top bar of the legs is redundant as it is hidden under the table.
Get rid of it and make the legs a big upside down C.

Then make some mortises in the bottom of the table top and plug the legs tightly into those. Attachment problem solved and it will break down nicely for transport.
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post #11 of 19 Old 04-02-2018, 12:19 PM
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Quote:
Originally Posted by andr0id View Post
The entire top bar of the legs is redundant as it is hidden under the table...Get rid of it and make the legs a big upside down C...Then make some mortises in the bottom of the table top and plug the legs tightly into those. Attachment problem solved and it will break down nicely for transport.
If I may make a critique of that advise please...

Having designed and built similar fashioned furniture to this current configuration, taking the bar away would not create an opportunity for a stronger joint union to what the OP has in their design at this time...

"The entire top bar of the legs"...are not redundant... at all. They do play a very critical roll in not only the joinery system, for say something like a sliding dovetail assembly with wedge...but actually add further stiffening and strengthening the table against oblique racking.

That is my observation/experience with such designs as this...

j
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post #12 of 19 Old 04-03-2018, 06:16 AM Thread Starter
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Ok I'll consider the steel legs idea for sure, that would be a lot stronger for sure ! I'll also look into a sliding dovetail . Thanks a lot guys !
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post #13 of 19 Old 04-06-2018, 09:03 AM
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Quote:
Originally Posted by charlo489 View Post
Ok I'll consider the steel legs idea for sure, that would be a lot stronger for sure ! I'll also look into a sliding dovetail . Thanks a lot guys !
Hi Charlo,

I do want to stress again that I like your design, and think you should stick with it!

Could it be stronger...sure, almost any design can be "stiffened" but at what point does that just become nonsense and redundant?

What are you designing for...A game room foot rest or an elegant coffee table...???...I take from your first sketch you are looking for the latter?

I thought of you today, when this was sent to me...

Is this the concept you had in mind, or something like it?








Below are similar formats in design, but with a different affect:








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post #14 of 19 Old 04-06-2018, 10:28 AM
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types of joints

A basic joint made of 2 pieces screwed together at 90 degrees relies entirely on the screws for strength. If the screws pull out or break off the joints fails.

We could glue the same joint and add more strength. The glue will bond to the wood and add shear strength or resistance to rotation, a better approach.

We could "let in" or mortise the vertical piece into the horizontal piece like a lap joint. This adds even more strength because the shoulders can resist rotation much better than glue or screws alone.
Like in Jay's photo above:


The length of the vertical, in this case a table leg, plays a large role in how much force will be applied at the center of the joint, where it will rotate. The longer the leg, the more rotational force can be applied to the joint given the same amount applied at the end. Like a wrench used to turn a nut:


If there is nothing other than screws and glue to resist the rotation, at some point more force will cause the joint to fail.
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post #15 of 19 Old 04-06-2018, 11:24 AM
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Don't Use Screws...for sure!!!

Quote:
Originally Posted by woodnthings View Post
A basic joint made of 2 pieces screwed together at 90 degrees relies entirely on the screws for strength....
Good points...

Not applicable to my post or what I have been posting on this thread...

None of the coffee tables I just posted for the OP are "screwed together" they are all jointed and glued...

Just so we are on the same page. Screwed joints are too weak, we agree...and I haven't suggest to use them...

Thanks,

j
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post #16 of 19 Old 04-06-2018, 11:46 AM
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nor have I advocated using screws!

In fact, I made a pretty good case against using them... doncha think?

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #17 of 19 Old 04-06-2018, 12:01 PM
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Quote:
Originally Posted by woodnthings View Post
In fact, I made a pretty good case against using them... doncha think?
I guess I'm confused why its necessary to keep bringing up...not using screws?

Quote:
Originally Posted by charlo489 View Post
...Ok I want to build this coffee table,...My only question is what would be the best way to attach the square legs to the top besides using lagbolts ?...
They seemed to not want to use hardware or metal from the very beginning of the thread...?

I got a email this morning that had almost exactly the table the OP requested. I was trying to be helpful again, and thought I would share the examples I just received.

Its been pretty plane I don't like hardware and I don't recommend using or relying on any. So I post some furniture examples (like the videos) that don't use any...

So...why bring screws up again...No body had or suggested using them?

I'm trying really hard here to be helpful, but it seems I can't post without getting "counter posted" about something or another unrelated to anything I'm writing about...???

We can agree...screws and lag bolts are a bad idea!!!

But then again... I don't think the OP wanted to use them in the first place...and I never gave an example of using them...

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post #18 of 19 Old 04-06-2018, 02:31 PM
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An anlysis of joints, strengths and types .....

Quote:
Originally Posted by woodnthings View Post
When joining/attaching elements that are in different planes, especially at 90 degrees, the strength is either in the joint or the means of attachment..... HUH?

Joints can be structural in themselves, like mortise and tenon, half laps, or dovetails. If you don't make the joint itself structural, the strength comes only from the screws or glue holding it together ... not good.

A butt joint, especially involving end grain to either end grain or long grain relies on the glue bond which is the weakest type. Long grain to long grain is the strongest bond glue will have.

As far as your table design goes, the 90 degree joints in the frame corners will not withstand any lateral forces, like a push from the side or end, IF miters or butt joints are used. Typically, that design is made by laminating thin layers over a form with radiused corners providing great structural strength. Then the issue of attaching the flat top bar to the bottom of the top becomes primary. Screws up through the bar would be typical. A recess for the bar to sit in, a shallow mortise, would add strength.

To make that type of table that will endure the rigors of time requires a thoughtful analysis of the forces and the methods of joinery. Glue is simply not sufficient. Similar table have been nailed and glued or screwed together, but they will not last. Typically, these days a welded steel frame is used, not wood and that provides the strength required.
Quote:
Originally Posted by woodnthings View Post
Have you ever sat on coffee table? Have children ever stood on a coffee table? The dovetails may be just fine, but it would be a shame to do all that work and have a failure. Make a few test samples and test them, that way you'll know for sure.
Quote:
Originally Posted by woodnthings View Post
A basic joint made of 2 pieces screwed together at 90 degrees relies entirely on the screws for strength. If the screws pull out or break off the joints fails.

We could glue the same joint and add more strength. The glue will bond to the wood and add shear strength or resistance to rotation, a better approach.

We could "let in" or mortise the vertical piece into the horizontal piece like a lap joint. This adds even more strength because the shoulders can resist rotation much better than glue or screws alone.
Like in Jay's photo above:


The length of the vertical, in this case a table leg, plays a large role in how much force will be applied at the center of the joint, where it will rotate. The longer the leg, the more rotational force can be applied to the joint given the same amount applied at the end. Like a wrench used to turn a nut:


If there is nothing other than screws and glue to resist the rotation, at some point more force will cause the joint to fail.
Quote:
Originally Posted by woodnthings View Post
In fact, I made a pretty good case against using them... doncha think?
Of the 234 views of this thread so far, I account for 4, Jay accounts for 5 and the Op has 3. That leaves 223 views by others. It may be useful to others to understand the basic types of joinery, their properties and applications. That was the purpose for my posts, to inform, not to advocate. Sorry for any misunderstanding.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #19 of 19 Old 04-26-2018, 09:10 AM
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I would attach the legs to the top with a motise and tenon. Maybe make the legs a little beefier for a bit more stability, you could even do a through tenon with some wedges. Maybe even cut a shoulder on the tenon for some added stability. I think you would be fine with wood. But then i'm a bit bias and kind of hate this trend of a gorgeous slab with some crappy bent round bar bolted to the bottom.

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