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Forum topic by bolandrm posted 07-14-2019 05:05 PM 277 views 0 times favorited 7 replies Add to Favorites Watch
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bolandrm

2 posts in 34 days


07-14-2019 05:05 PM

Topic tags/keywords: joining

Hey, I’m a long time lurker, but this is my first post. I’m designing a large circular dining table, and I’d really appreciate it if anyone could take a look at the design and joinery and let me know if there are any potential problems.

The table is 72” in diameter, and the top is 30” off of the floor. It will be made entirely of white oak. Here is the overall design:

The feet will probably not end up being that long. I plan to do a mock up of the base with construction lumber to determine the best length for the feet to ensure there is enough stability.

I’d like the top to be 1 1/2” in thickness, but I’m worried about the weight of such a large and thick top. So what I decided to do instead was to cut the end off of each board, flip it over, and glue it back on itself to create a thicker edge of the table. I’ve seen this technique in other posts on the forum.

Here is an exploded view of the joinery. Mostly mortise and tenon + half laps. I’m a little unsure of the M&T joints on the main column combined with the lap joints. Will all of the different joints weaken the wood too much? Is there a better joint combination I could use here?

The table top will be bolted to the base via elongated holes to allow for wood movement.

To summarize, here are my main concerns / questions:

1. Will all of the M&T joints in the main column weaken it too much?
2. Are there any guidelines for the length of the feet for a 72” table top?
3. I don’t have a very good bandsaw. I’m concerned about doing the radius cuts on the feet, as the bandsaw might not have enough power. Are there any other approaches to doing this?

Thanks for looking! If anyone is interested in the designs, I can post the sketch file.


7 replies so far

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Aj2

2377 posts in 2245 days


#1 posted 07-14-2019 06:51 PM

Your top design is over complicated. Maybe you’ll be able to hide all the glue lines maybe not.
Make your life easy and buy 6/4 boards that look nice together. Always get one or two extra just Incase you have several that are not behaving.
5/4 top will look plenty thick. There’s ways to profile the edge to make it look thicker or thinner
Good Luck

-- Aj

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Lazyman

3661 posts in 1835 days


#2 posted 07-15-2019 02:10 AM

As long as the M&T joints are nice and tight, it should not weaken the column. Once the tenon is glued into the mortise, it will be nearly as strong as it was before, Besides, the braces are there to absorb most of the stress that would break it.
For cutting the curve on the feet you could cut grooves at about 90° to the curve so that you are removing small wedges as you make the curve. Just take your time. This should put a little less strain on the bandsaw . Just don’t cut all the way to the line and finish shaping with a rasp and/or disk or belt sander

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

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Delete

439 posts in 820 days


#3 posted 07-15-2019 03:03 AM

I agree with Aj2 and Laxyman with regards to the top and forming the base legs. Your sketch up doesn’t include any measurements, the weak spot I see is the 2 or 3 inches I see between your top and bottom braces on your central post. Your post end mortises will not be taking alot of force. Any forces developed by twisting action will get transfered to the middle of the center post by the bottom braces or the top braces or both. Also the 3’ to the center of the table will have mechanical advantage over the center of the post which is less than 1.5’ from the top or bottom, 50 lbs. leaning on the edge of the table will be much greater, trying to break the center of the post in half, between the braces. For a 6’ table top you need a much larger center post. The center post on my 44” round table looks twice as large, though it is glued up, turned round and hollow. To keep the table from tipping the length of your feet should be close to 4’6” for that 6’ top.

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bolandrm

2 posts in 34 days


#4 posted 07-16-2019 01:04 AM

Thanks for the feedback everyone.

Regarding the top, I agree it would be better to use 6/4 lumber, but the only hardwood dealer in my area only carries 4/4, 5/4 and 8/4.

Carlos, thanks for the feedback regarding the weak point in the middle. I’ve revised the design to (hopefully) account for this. Perhaps it doesn’t cover the twisting action as much, but it will hopefully account for the more likely leaning down on the edge of the table.

The center post is 3 1/2” square. I do plan to build a prototype base from construction lumber. That should give me a good idea of whether it will be strong enough.

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Delete

439 posts in 820 days


#5 posted 07-16-2019 01:55 AM

You must have some design background bolandrm, thats great. Twist was probably the wrong word to use I was referring to the action of applying pressure to the table top, applying forces to the center post. Your modification looks great and should solve the problem by transferring forces to the floor legs through the bottom braces rather than concentrating them in the center of the post. For joinery you might want to avoid cutting 8 mortises close to each other at the center of the post and go with four mortises only. Register smaller tenons on the top and bottom braces into one mortise. Avoid cutting shoulders on the tenons where the braces come together so they form one tenon to fit into the mortise on the post.

3 1/2” square center post still sounds small to me for such a large table top, but I have not done much work with oak. 4 1/2 or 5” would be more my preference, but I imagine you are going for a favored look and building a prototype to check it out is a good idea.

View AndyJ1s's profile

AndyJ1s

43 posts in 203 days


#6 posted 07-17-2019 02:28 AM

A couple of thoughts…
1. Consider having the tops of the lower diagonal braces mortised into the bottom side of the upper diagonal braces (or vice-versa), to reduce mortises in the center column. Not sure what it might look like aesthetically.
2. Alternatively, consider extending the upper and lower diagonal braces so they cross each other (half-lapped), and extend 2/3 or so towards the opposite end of the column. Note the diagonal braces would no longer be 45 degree angles, but maybe 60/30 (more vertical).
2. Consider reducing the size of the tenons at top and bottom of column. The mortises into the middle of the half-lap joints in the top and bottom pieces are not leaving much wood in the cross-members.

Andy

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therealSteveN

3353 posts in 1022 days


#7 posted 07-17-2019 04:59 AM

This table is very current here

A lot of similarity between what you have, and it. I’d follow the leader. Typically I am not a fan of these “tippy” tables, and much prefer the good old farmhouse, but this one looks very stable.

-- Think safe, be safe

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