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Forum topic by LutherVandrossJr posted 08-16-2019 07:17 PM 272 views 0 times favorited 5 replies Add to Favorites Watch
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LutherVandrossJr

3 posts in 35 days


08-16-2019 07:17 PM

Topic tags/keywords: question ash

Hey everyone, relatively inexperienced woodworker here. I’m looking for a reality check on a pedestal table design I’m about to build. I’m worried about stability, particularly the propensity to tip over or shear the top from the pedestal. The client is my gf’s mom, so if this goes wrong I look forward to hearing about it at every holiday for the rest of my life. Pics attached https://imgur.com/ik2m7MT

It’s all ash. The top is oval, 1 5/8” thick, 6’ x 3’, made of dominoed 4-5” wide boards with alternating ring orientation. The pedestal column consists of an X-shaped tapering column (5” across at the base, 3.5” at the top) sandwiched between two hexagonal pieces (bottom hexagon is 3.5” thick, top is 1.5” thick). I’m planning to run a threaded rod through the column to lock these parts together and screw the rod into a threaded insert on the underside of the table.

Also under the top is a substructure of 1.25” thick ash (not quite an apron) that screw/dominos into the top along the long axis. Elsewhere, I’m planning to attach the substructure into the top using something that accomodates expansion. Hopefully this should be sufficient to keep the top from warping, which should be minimal anyway.

The feet are 20” x 3” x 1.5” and are dominoed into the bottom hexagon. They extend the X shape of the central column—if they were on a clock face they would hit the 2, 4, 8, and 10 (60, 120, 240, and 300 degrees). I’m considering adding weight to the underside of the bottom hexagon but haven’t decided that one yet.

I really don’t want to make a table that tips over or falls apart if someone sneezes on it. Any advice would be greatly appreciated.


5 replies so far

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Aj2

2431 posts in 2280 days


#1 posted 08-16-2019 07:34 PM

I looked at your image. And it does look tippy from that perspective.
But it think it’s doable
If it were my build I would made the four feet extra long .
Then cut them back till they looked right and felt sturdy.
Good luck

Ash is a nice wood to work with.

-- Aj

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LutherVandrossJr

3 posts in 35 days


#2 posted 08-16-2019 07:38 PM

That’s great advice, thanks. I’m definitely going to do that.

View CaptainKlutz's profile

CaptainKlutz

1776 posts in 1976 days


#3 posted 08-17-2019 12:05 AM

Hmm, have built a couple of pedestal tables?

1) One tip I learned: heavier you make the center column, the more stability you have at center of table mass. When you use small diameter column, you are dependent on the weight, span, and angle of legs to provide stability.
Only having a 3.5” wide support at top is on small side for 6” wide table, but should be ok due to the 3’ ft rectangular side assuming proper leg length as suggested above. Key point being that as the center post gets larger, the length of fulcrum at edge decreases, and stability increases.

2) When you attach cross braces on the lower half of supporting column, you reduce stability of table. The braces need to be above the center point of the column. Again it is physics. Attached below the center, this increases the length of moment arm, and reduces the amount of force required to tilt the base.
If this is a design element you need to keep, note that having those long table top braces attached near bottom of column will force you to have longer legs to create stability.

3) Look closely at your pivot points, and length of lever arms in the design.
If you look up most of antique french table designs with small turned center columns, you will note that they mount under table supports no more than 25% of total height from the top, and usually mount the legs high on the center column to provide the highest leverage and stability, which also enables smaller structures. Your design has the legs very near the floor, and this doesn’t provide as much stability as moving the attachment point up further.

PS – #IAMAKLUTZ engineer who over designs everything, not an expert.

Best Luck.

-- I'm an engineer not a woodworker, but I can randomly find useful tools and furniture inside a pile of lumber!

View AndyJ1s's profile

AndyJ1s

57 posts in 237 days


#4 posted 08-18-2019 09:03 PM

Is this an occasional table or a small dining table (how high is it)?

I think you are going to need diagonal bracing between the feet/legs and the center column. Similar arched braces, half-lapped with the upper braces might look good. They would re-enforce each other to resist flexing too.

You might also consider a 12 sided column, with the upper braces at 12, 3, 6 & 9 o’clock, and the lower (leg/foot) braces at 2, 4, 8 and 10 o’clock.

Without braces, you might get by if you make the legs two pieces instead of four (half lapped in the middle), and a bridle type joint to the column, but not with four single piece, 3” tall feet/legs.

I think I’d build a prototype first out of SYP & construction grade plywood to get the size and balance nailed down.

Andy

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LutherVandrossJr

3 posts in 35 days


#5 posted 08-19-2019 11:43 PM

Thanks both of you. Great advice.

It’s a dining table but I don’t think it’s going to get daily use – top is 29”.

Unfortunately the curved braces are nonnegotiable, but I can move them up the column.

Moving the attachment point of the feet up is a great idea. My original design had that feature but I was worried about the stress on the feet where they leave the floor. I’m either going to do that or run the feet through the base with a half lap.

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