Big table top!

[iublue]

I am finishing up what I consider an odd sized table.  It is 5' x 5' out of 1 3/8" thick walnut.  Heavy top, so heavy that since I work by myself, I had to design a apparatus to move and flip the top over.

The schrinkulator calculates an 1" of movement if I put in the high value of 12% and the low value of 6".  I would think that would be the extremes or at least I hope so!

I was going to use figure eights to fasten the top to the apron but I am concern that figure eights would not handle that much possible movement.  Thoughts?

The base is 35" x 35" with 5" x 5" legs and 2" x 5" aprons.  I was only going to put the figure eights parallel to the grain.  Would it be a mistake not the attach the sides of the table to the base in some way?  Once again, there is a potential of a considerable amount of movement.

Thoughts?

Thanks,

Toney

[Bill Holt]

No expert here...but I built a 60" round walnut table for our daughter about 15 years ago.  I believe it was John Fry who gave me the courage to move forward.  The brain trust here, offered the opinion that since the top was a glue up of 6-to-8-inch boards the movement would be drastically reduced, especially in a controlled indoor environment. I used figure eights and there have been no issues.

[jteneyck]

It's good to plan for the extreme, and hope it never happens.  Much better than the other way around.  I don't really understand how figure 8 fasteners allow for wood movement w/o something pivoting, just seems odd to me.  I would use buttons or Z-clips on the aprons where the top goes cross grain.  I made this table a few years ago, something like 42" x 96".  Here's what the base looked like.




Not shown here, but I cut a dado around the inside edge of the end aprons and cross stretchers with a biscuit jointer.  They cut a perfect groove for Z-clips.  Three clips along each member.  The top can do as it wants with no worry of binding/splitting from how it's held to the base.  Bonus points if you add a dowel locator at the center of the short aprons to center the top or, alternatively, use pocket screws.  I didn't.  

john

[wing nut]

No expert here...but I built a 60" round walnut table for our daughter about 15 years ago.  I believe it was John Fry who gave me the courage to move forward.  The brain trust here, offered the opinion that since the top was a glue up of 6-to-8-inch boards the movement would be drastically reduced, especially in a controlled indoor environment. I used figure eights and there have been no issues.

off topic, but whatever happened to John Fry, I remember his post.

[jteneyck]

off topic, but whatever happened to John Fry, I remember his post.

He posted a couple of times a year or two ago, but then went dark again.  

John

[Stwood_]

I always figure a 1/4" shrinkage every 12" of width on air dried lumber. Kiln dried is much less normally, or should be.
I built a 5'x12' 2" thick oak dining table top that the customer wanted end caps. I hesitated, but did. So I told him I could not guarantee the table stayed matched to the end boards.
And it did not. I went back 2 months later to install 80' of bendable handrail on wrought iron newels and railings, and the table had shrunk a 1/4" on each side, exposing the bread board ends.

[blackhat]

Finish doing the math. At centre there is 0 movement if it’s fastened.   1/2” from center to each edge. Halfway from center to edge ( 15” ) there’s 1/4”. That’s more easily digested. It’s still more than I would be comfortable with fig 8s. Z clips or wood buttons with a tongue riding in a groove in the apron would be my choice.

[Gary G™]

I would use shop made buttons.