Attaching table top without apron


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How can I attach a table top without an apron to allow wood movement? The top will sit on 2 4x4s 38 inches long. Its a trestle style base. The top is built out 4 2x12s that were kreg jigged and glued together. I'm rebuilding the top because the wood dryed and seperated where it was joined together. Z fasteners and buttons won't work since there's no apron. I attached the top with screws and hanger bolts before, which now I've realized was a bad idea. Any help, thanks. Pictures are below. 

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1 minute ago, wtnhighlander said:

You can still use screws or anchor bolts through the upper member of the trestle and into the top. Just make sure to elongate the holes at the ends of tge trestle member to allow the top to move. And don't tighten the screws too firmly.

This is also correct and a good option!

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4 minutes ago, Alonzo said:

Do I drill a hole wider in the upper Trestle part so the hanger bolt can move side to side with the table top? While the hanger Bolt stays tight into the table top.

Yes, exactly that. If you use three bolts, the center can be a round hole, and tight. The two outer ones need room to expand.

Here is a tool to help estimate how much the top can move, and how long the holes need to be:

http://www.woodweb.com/cgi-bin/calculators/calc.pl?calculator=shrinkage

 

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5 minutes ago, Alonzo said:

Do I drill a hole wider in the upper Trestle part so the hanger bolt can move side to side with the table top? While the hanger Bolt stays tight into the table top.

Elongate with a rasp in the direction of the potential wood movement.  You can tilt your drill bit side to side as well, just be sure to keep it perpendicular to the grain in the top.

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I would drill 3 holes very close together then wobble the drill bit to connect them. You can drill a recess with a forstner bit if you want the bolt/screw head below the surface. I use a pan head screw with a washer. Install the screw in the middle of the slot so the top can expand or contract.

You could use the figure 8's in the center  and where the braces would make drilling through the top 4 x 4.

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I have one more question. I attached the breadboards with the kreg jig and glued. Then screwed and glued two 2x4 to the bottom to support it. The ends  are a  1/4" long now since the middle has shrunk. How can I fix this? Do I have to do a joinery joint to install the breadboard? Or is there another way? The breadboard is 10"x1.5"x42"

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1 hour ago, TIODS said:

Elongate with a rasp in the direction of the potential wood movement.  You can tilt your drill bit side to side as well, just be sure to keep it perpendicular to the grain in the top.

Did you mean parallel to the grain? 

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Ugg..  If you used the Kreg/glue and attached anywhere other than the middle, the misalignment you're seeing is probably the best case.

You have to allow for wood movement when building furniture.  Please chalk this up to a learning experience, you're not the first nor the last to make this mistake.

IF you only glued/Kreg at the middle, then be satisfied with the seasonal movement.  If you glued/Kreg all along the breadboard, you could be in for bigger issues or, you're lucky for now!

There's lots of YT videos out there on making BB ends.  There's also some free WW videos as well as some WW Guild videos on the process that would have helped before the build.

 

Wood moves!  Build to allow for it, you can't prevent it.

 

2 minutes ago, K Cooper said:

Did you mean parallel to the grain? 

No..  Wood expands across the grain.

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Ok thanks Tiods. Most the videos I saw were on breadboards that are not very wide, my breadboard is around 10 inches wide. Also, it does not rest on an apron, but a 2x4 I attached below to the top. How can I make it strong enough and allow movement without screwing it together? 

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Breadboard ends should be mounted with mortice & tenon joinery.  The tabletop will expand and contract over the year usually with the change of the season. The breadboard can be mounted fixed in the center but both sides will need to be able to expand and contract.

You could remove all the screws and cut the glued joint to remove the breadboard. All the kreg holes except the center one would need to be wobbled out into an oval shape so the wood can expand & contract. 

Wood will expand and contract across its width, it won't change length very much at all and the thickness will barely change. So the breadboard won't change length but the top will expand & contract. Softwood does it more than hardwood.

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Ok great. Do you think I could do a loose tenon for the breadboard so I can maintain the length of the table? The table is douglas fir. Could I use doug fir for the loose tenon?  If I do a loose tenon, how many would I need? I have four 2x11s joined together. I see a split tenon is common, however I don't get why people do that. Breadboards are to stop cupping right, so what difference does the tenon length make? Thanks for your help. 

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5 hours ago, Alonzo said:

Also since the bread board allows for wood movement , is it normal for the breadboard to expand outside of the long boards?

During warm, moist times the long boards will be wider than the bread board is long. During cold dry periods it will be the opposite..The expansion happens primarily in the long boards getting wider or narrower, not the breadboard getting longer or shorter. Wood movement occurs almost exclusively in the width, not the length of a board.

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I do not want to appear to talk down to you, but need to be certain you understand breadboard ends. The panel movement has been described well for two dimensions. Breadboard ends deal in the third dimension. They encourage a panel to expand with minimal cupping as humidity enters and exits either the top or bottom more quickly. They should capture some of the top or they serve only a decorative purpose. 

7 hours ago, Alonzo said:

Also since the bread board allows for wood movement , is it normal for the breadboard to expand outside of the long boards?

 

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8 hours ago, Alonzo said:

Ok great. Do you think I could do a loose tenon for the breadboard so I can maintain the length of the table? The table is douglas fir. Could I use doug fir for the loose tenon?  If I do a loose tenon, how many would I need? I have four 2x11s joined together. I see a split tenon is common, however I don't get why people do that. Breadboards are to stop cupping right, so what difference does the tenon length make? Thanks for your help. 

Loose tenons are perfect...you just need oversized mortises for the outer joints just the same as if they were integral mortise and tenons.  There are lots of videos on YouTube that explain how breadboard ends work. 

As for how many, I'd place them every four to six inches. 

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