how to pevent open miter joints

[Norris Randall]

Greetings, I have agreed to help a friend build a table top.
Vary widths of top 3-4-5 -? inch.
He wants to FRAME with a 3 or 4 inch wide mitered outside.
table.JPG

I am concerned that the miter joints will not remain stable with
changes in moisture.
Present plan is to use biscuits every 4-6 inches to glue edges.

Friend thinks he would like to use two different woods.

Thank you for all suggestions for any and all phases of this job.

[IMG]file:///C:/DOCUME%7E1/NORRIS%7E1/LOCALS%7E1/Temp/moz-screenshot.png[/IMG]

[Leo Graywacz]

Yep, that design will pop the miters. If you make the field float like a raised panel you can frame it with the miters like you have shown. Otherwise the shorter miters on the end grain will pop eventually.

If the table is less than 22" wide you may have a chance, wider than that, trouble.

[Ryan Sparreboom]

I don't think the answer is as easy or as definite as Leo is suggesting.
What type of wood are you using for the center pieces? How is it cut? How thick will it be? How dry is it to start with? What finish are you planning to use?

Heres the thing, I think it CAN be done. If you are using well dried, stable, quarter sawn , thin lumber for the middle, and finish it very well, you will see almost no movement and a solid miter frame is possible without it blowing apart on you.

If you are real worried and/or can't get the above things lined up, then I would suggest you use a veneered top on a stable substrate like MDF, and frame that with solid lumber, to alleviate all concerns.

HTH

Ryan

[Norris Randall]

Thanks Ryan & Leo,
We purchased the wood today. Mahogany for the center and walnut for the frame/edge.

Friend wants to keep thickness around 7/8". and has mentioned glue/screw plywood to the back.

What thoughts does anyone have regarding this idea?

"pevent" = prevent
I need a "poof" reader.

[Leo Graywacz]

Bad idea, unless you want the top to cup. Let it free float.

[Lee Schierer]

Yep, that design will pop the miters. If you make the field float like a raised panel you can frame it with the miters like you have shown. Otherwise the shorter miters on the end grain will pop eventually.

If the table is less than 22" wide you may have a chance, wider than that, trouble.

I agree completely with Leo. Based on your 7/8" thickness for the center area you will need to make the center panel float regardless of how dry the lumber is now to avoid gaps in the miters and you will not want to glue them across the end grain. I would attach the end pieces with a sliding dovetail to keep them tight to the filed but let them float. In addition I would reinforce the miters with pocket screws on the underside and apply equal amounts of finish to the top bottom and sides of the table top to slow down seasonal moisture changes. Use a tongue and groove on the side pieces to keep them aligned with the field.

[Mike Wilkins]

Only way I would attempt something like your diagram is with a floating panel in the mitered frame. Solid wood will move, even if it is finished on all sides. It would be impossible to control the environment around this table top, as the changes in temp/humidity are constant. You might have some luck with a veneered panel, using MDF as a substrate. Good luck and happy mitering.

[Bill Arnold]

I vote for no miters at all to play it safe. You can get a similar appearance by using the mahogany for the center boards and walnut for the outside edge boards on the sides. Then use walnut for a breadboard end on both ends. The breadboard end allows the field to move.

[John Thompson]

I vote for no miters at all to play it safe. You can get a similar appearance by using the mahogany for the center boards and walnut for the outside edge boards on the sides. Then use walnut for a breadboard end on both ends. The breadboard end allows the field to move.

Agree with Leo.. then Lee... then Mike. And a vote to consider what Bill stated about the bread-board end as a strong possibility. The original design might hold awhile or blow a gap in a week if conditions are right.

Good luck...

[Darrell Hampton]

You can get the look you want by using veneer over MDF or lumber core plywood. It would be very stable, flat and strong. Miter the corners of the walnut band you want to use and when it moves everything will move together. The alternative is constant worries about miters coming apart and cupping boards on the top.