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Designing legs for 14’ x 5’ conference table.

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Forum topic by Mark posted 11-20-2018 01:50 PM 343 views 0 times favorited 9 replies Add to Favorites Watch
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Mark

40 posts in 474 days


11-20-2018 01:50 PM

I’m constructing a 14’ x 5’ conference table out of what’ll be Oak with finished thickness 1 3/4”. The client showed me a picture of the legs they’d like, but I wanted to run it by you guys to see if you thought my plan would hold up.

You can see from the image that all the joints are right angles. I purchased the Leigh D4R so that I can make blind dovetails in 1 1/2” stock, and that’s what I plan.

With the material I have (they provided it) I can make the legs 4-6” in width, and 1 1/2” thick. I know that the blind dovetails will be plenty strong for the legs going widthways, but it’s the long run that concerns me. What will the racking be like on a table this size? I can brace the joints on the underside of the table, and they wouldn’t be visible, but I’m not sure if that’s enough.

Rather than having all the joints be 90s, would it be significantly stronger to build the base as a trapeze shape, with the legs angling inwards on the way down?

With my material, I can only make the base 8’ long on the 14’ table, with means 36” overhang on each end.

Any thoughts would be greatly appreciated.


9 replies so far

View mahdee's profile

mahdee

4020 posts in 1965 days


#1 posted 11-20-2018 03:48 PM

Hi,
To me the base design doesn’t make sense. The verticals are too close to the edge which will cause a problem as it relates to chair spacing. How far apart are you going to have the verticals?

-- earthartandfoods.com

View Mark's profile

Mark

40 posts in 474 days


#2 posted 11-20-2018 03:57 PM

With an 8’ run on the base, I could start those side supports 1’ from each end, then have either one or two spaced in between.

If I angle those inwards on the way down, they would be far enough away such that chairs can push under. I was planning to set the verticals 12” in from the table edge.

My main concern though is the run lengthways down the table. I don’t know how to know if it will be strong and resist racking.

View MrRon's profile

MrRon

5190 posts in 3441 days


#3 posted 11-20-2018 04:03 PM

My choice would be a box base, 3’ wide x 12’ long. I really don’t like the client’s base.

View Mark's profile

Mark

40 posts in 474 days


#4 posted 11-20-2018 04:19 PM

I see that other large tables are supported this way. Is the trapezoid much superior than a square in terms of racking? In my circumstance I’m concerned mostly about the run up and down the table, not side to side.

If you imagine the image above, with a third base in the center, an elongated lengthways trapezoid and all joints are dovetailed, I want to say that I’m confident that’s a lot of strength. But obviously I’m here because I’m unsure..

Edit- awesome photoshopped image below, depicting what’s in my head.

View Aj2's profile

Aj2

1867 posts in 1995 days


#5 posted 11-20-2018 04:39 PM

14×5 ft table from solid wood that’s crazy talk.

-- Aj

View mahdee's profile

mahdee

4020 posts in 1965 days


#6 posted 11-20-2018 05:19 PM

Regardless of the angles, the force will still be straight down as far as I know. Maybe some of the engineers can chime in. I can see having two runners on top and bottom of the base would support the top well but I don’t think 1-1/2” legs would look proportionate.

http://www.recobklyn.com/slab-furniture.html#

-- earthartandfoods.com

View GrantA's profile

GrantA

673 posts in 1605 days


#7 posted 11-20-2018 05:31 PM

^^what AJ said…sounds like about a $14,000 table to cover the headaches.
I think you’re on the right track with the sketch above, no way would I want so much overhang as mentioned though (36”). If you need more material just tell them. Even if it means getting different wood for the base.

View Mark's profile

Mark

40 posts in 474 days


#8 posted 11-20-2018 05:38 PM

I’ll look into what the jig can do, as my leg stock is about 9/4, so I won’t take it all the way down to 1 1/2” if I don’t need to. (Edit: if necessary, I’ll rip it down to 1 1/2” to cut the dovetails, then laminate it back on.)

I can reduce that overhang but only by joining two boards. If I make the base a trapeze I can keep the visible beam (that runs along the floor) 8’ and do staggered laminations to make the top beam 10’. I’ll sketch it up and see if that angle will look good. Material is limited as the lumber comes from land cleared for a subdivision. It’s got a lot of “character”, so I can’t just purchase more wood. I have more of it, just nothing in lengths exceeding 8’.

Not quite $14,000 but close.

View bilyo's profile

bilyo

415 posts in 1300 days


#9 posted 11-20-2018 06:12 PM

I think that your idea about putting the verticals on an angle is good from an aesthetic and functional standpoint. Structurally, however, I don’t think it makes much difference. The resistance to racking is going to be all in the joints in either case. Mahdee’s drawing above shows these members on edge which would contribute to the strength of each joint. Your idea of a top rail will also contribute to over all rigidity. Consider getting some construction lumber (2×6 etc) and experiment with different joinery. With the leg and rail members on edge, IMO, splined miters (maybe with a couple of pegs) would both look good and provide the strength and rigidity you need. Mortise and tenon would be my second choice. Considering the time and trouble to do it, I don’t think dovetails would provide any benefits in this application.

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