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Adjusting Table Design to Account for Wood Movement

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Forum topic by Saucerito posted 01-04-2016 02:29 AM 651 views 0 times favorited 9 replies Add to Favorites Watch
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Saucerito

12 posts in 336 days


01-04-2016 02:29 AM

Topic tags/keywords: question

Hi everyone,

I’m just getting started building a table for my house, and found this design that my wife likes. The project overview can be found here. Since this will be my first real woodworking project, I’d like to keep the material costs relatively low.

I will be using red oak for the table top instead of pine, and using a breadboard (for asthetics) rather than trim as shown in the plan. The overall table top dimensions may vary slightly as well. My primary concern with this design is that it doesn’t seem to account for the movement of the table top. My thought was to screw down the middle of the supports (possibly with pocket holes), and use table top fasteners to attach the remainder of the supports. What do y’all think about that? Can I do something similar with the breadboard? I’d prefer to not have to deal with mortise and tenons as that is something that I don’t know how to do, and probably don’t have the tools for it.

Tools I own or can borrow easily:
Drill
Impact Driver
Circular Saw
Miter Saw
Palm router
Kreg Jig

Thanks, Will


9 replies so far

View Nicky's profile

Nicky

695 posts in 3553 days


#1 posted 01-04-2016 05:30 PM

The design does not seem to take into account the movement of the top and you are wise to notice.

Securing the top from the center will work, pocket holes or just directly screwed through the supporting member.

If the table top fasteners you refer to allow for movement, then you’re good.

The breadboard is a key component for success, and a tenon will be required. The idea is to glue the center of the tenon only, and pin each end with a dowel. The ends of the tenon (where the dowel hols are) should have elongates holes to allow the table top to expand and contract. Search you-tube for some video examples.

With your circulate saw and a sharp chisel, you can create the tenon. With a drill and sharp chisel, you can create the mortise. You could also use the palm router to make the tenon.

Look at it as a challenge and skill builder. This will be well worth your time.

-- Nicky

View WhyMe's profile

WhyMe

612 posts in 1022 days


#2 posted 01-04-2016 05:47 PM

I believe that design requires no gluing and is put together with only pocket screws. Being only screwed together is forgiving enough to probably allow wood movement. If the top was glued up as a solid panel using bread board ends without allowing for movement in the top would most likely cause the top to crack.

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jdh122

879 posts in 2279 days


#3 posted 01-04-2016 06:00 PM

It’s true that if you screw the end pieces of the frame around the top rather than gluing them you might just get away with it using softwood (which moves less seasonally than does hardwood) but personally I’d be reluctant to take the risk even with pine. Breadboard ends are a good idea (done as Nicky indicates). The way the table is attached is another problem that will probably lead to cracking in the table. You could use screws put into elongated slots in the top of the trestle, except that you can’t with this design since the . z-clips or shop-made wooden buttons (https://www.finewoodworking.com/media/TabletopsFlat.pdf) would work, I suppose.
Or you could pocket screw the top down to the middle of the tressle (shown in pink in picture 13 on your plan) and put screws in slots on the end of the board pictured in grey in picture 13.
Or better yet, Stop building the base at step 8 and you could screw up into the table (again, with elongated holes ro slots toward the sides).

There is no reason to pocket screw those boards together for the top, just glue and clamp.

-- Jeremy, in the Acadian forests

View rwe2156's profile

rwe2156

2190 posts in 942 days


#4 posted 01-04-2016 06:43 PM

What Nicky ^ said X2.

-- Everything is a prototype thats why its one of a kind!!

View Saucerito's profile

Saucerito

12 posts in 336 days


#5 posted 01-04-2016 07:53 PM

Thanks everyone for the replies. The table top fasteners (or S clips or Z clips or whatever) would allow for movement of the table top. I like the idea of screws with elongated slots too however.

I will be gluing the boards for the table top.

Would it be possible to do the trim as shown in the original plans, but with 45 degree mitered ends? It seems like a noticeable gap would be created between each trim piece as the table top expands and contracts.

View jdh122's profile

jdh122

879 posts in 2279 days


#6 posted 01-04-2016 08:33 PM

You’re right that a noticeable gap will be created with the trim as the table expands and contracts. In fact the expansion and contraction of the table will tear the frame apart, regardless of whether the ends are mitered or butt joints, even if you use breadboards on the ends.

One disadvantage (or peculiarity, if you prefer) of breadboards is that they are flush with the sides of the tabletop only twice a year, when the seasonal humidity is the same as when you made it. But the disadvantage of the tabletop as shown in that drawing is that it basically can’t exist unless the inner part is made of plywood.

-- Jeremy, in the Acadian forests

View ThomasChippendale's profile

ThomasChippendale

244 posts in 394 days


#7 posted 01-05-2016 12:45 AM

You are so right Jeremy, it is an odd design and has several flaws other than the top frame. The trestle should have the bottom beam extend the full-length and the table top to trestle assembly is equally overcomplicated and restrains the wood movement. It is also not elegant, looks like its from a structural steel designer, but if you like the looks of steel bridges it can have its charms.

If you are going to build it , stick with your first idea of having a breadboard or use an apron with the end boards extending over the ends of the long apron boards (opposite of how it is designed) and attached to the top with screws to the top in the middle and with clips in a grove in the apron http://selbyhardware.thomasnet.com/viewitems/table-hardware/table-top-fasteners. You could actually use the exact same design but have the end boards extend to the edges instead of the long side frame boards, and attached to the top as mentioned above.

You can assemble the apron that goes lengthwise with the top grain with screws, better you could even only glue it.

The trestle cross beams intersecting the lengthwise bottom beam should have a half lap joint, and you get a single long screw to hold them in place across the crossover center http://woodworking.formeremortals.net/2015/03/contemporary-photo-frame/
You should fasten the trestle to the top using those same clips so it also allows for wood movement.

-- PJ

View Saucerito's profile

Saucerito

12 posts in 336 days


#8 posted 01-08-2016 11:59 PM

PJ,

I will try to simplify the trestle assembly as you mentioned. I’m also going to build apron part with the short ends extending over the long ends.

Thanks!

View ThomasChippendale's profile

ThomasChippendale

244 posts in 394 days


#9 posted 01-09-2016 04:08 AM

This apron configuration will keep the top from spliting when drying since the original configuration kept the top from shrinking in width. Do not hesitate from simplifying this design, it is un-necesssarely complicated. Keep your efforts in making it nice and well assembled and finished.

-- PJ

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