Advice re thickness for tabletop - Router Forums
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post #1 of 24 (permalink) Old 01-16-2017, 05:51 PM Thread Starter
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Default Advice re thickness for tabletop

The "Director of Home Economics" wants me to make her a table out of Macrocarpa. Top will be 2.5m long and consist of several (6 or 7) boards 200mm wide. but she does not want breadboard ends. Legs will project up thru the top and finish level with the top of the table. The table will finish with a sandblasted/distressed look

My question is how thick should I make the boards given that I need to be able to move it without calling in a team of men to help but at the same time I want to minimise (prevent) any sag over that length. Would 30mm (approx 1.25") be sufficient or could I get away with 25mm (1")

Hmm this might also be a good project to start to learn Sketchup with ....unless I can find some suitable plans as a basis.

Alan
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post #2 of 24 (permalink) Old 01-16-2017, 06:29 PM
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25mm top and add 25mm thick closed grid for strength and a faux 50mm...
arrange the grid to reinforce the table legs..


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post #3 of 24 (permalink) Old 01-16-2017, 09:24 PM
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Alan, I made a table top for a lady and it was so heavy, two of use could hardly pick it up. It was made from hard maple. The final thickness was just shy of 1 1/2 inches. Seems like it was about 39 x 65 inches or something like that.

I had to glue up the boards in several sessions. It dwarfed my poor little work bench. But she loves it.
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post #4 of 24 (permalink) Old 01-16-2017, 09:50 PM
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Mike - I looked at your first picture and wondered why you had full 2 x's clamped to your workbench - and then when I looked at it more closely, realized that those are some large frikken clamping cauls!!

Nice looking table, but given the width of your material (seems to be 5 @ roughly 8" across), what have you done on the underside to prevent warping?

Do you have a picture of the underside?

Thanks

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post #5 of 24 (permalink) Old 01-16-2017, 10:57 PM
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Originally Posted by vchiarelli View Post
Mike - I looked at your first picture and wondered why you had full 2 x's clamped to your workbench - and then when I looked at it more closely, realized that those are some large frikken clamping cauls!!

Nice looking table, but given the width of your material (seems to be 5 @ roughly 8" across), what have you done on the underside to prevent warping?

Do you have a picture of the underside?

Thanks
4x4's. It's all clamped together. And it turned out good.

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post #6 of 24 (permalink) Old 01-16-2017, 11:03 PM
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I would agree with Stick that 25mm would be a minimum and probably around 35 a maximum. Be aware that boards that wide will be prone to warpage as someone else mentioned. One way to help prevent that is cut saw kerfs into the bottom of the boards about 25 to 35% of the top thickness and I would go about 30 to 35mm apart. This helps to release some of the stresses in the board as it changes temperature and humidity.

You also have to allow for changes in board width as their moisture contents change from season to season. I usually make my tops to sit on a frame with aprons from leg to leg and use these Tabletop Mounting Clamps - Lee Valley Tools to attach the top to the frame. This allows enough movement to prevent cracking of boards or joints. A woodworking friend of mine prefers to make his out of wood but the principle is the same. Here is another method of attaching tops: Expansion Washers - Lee Valley Tools Same general idea in that it allows the connector to slip as one side moves against the other.

I would personally avoid having the legs go through the top. I would want a member between the legs cross ways for support, otherwise you are depending on glued butt joints to hold the weight up and the cross member wouldn't allow for expansion and contraction. Maybe someone elses experiences are different than mine though.
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post #7 of 24 (permalink) Old 01-17-2017, 12:22 AM
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Chuck, I'm with you on not having the legs go right through the top. My reason is that the top wood will move more than the leg wood, because the grains will be running 90º to each other. So you might end up with a leg either protruding very slightly or receding very slightly from the top surface of the table.

Unless you want an arts and crafts type appearance to the top, then in that case you could deliberately have the legs protrude 1/4" or so.

As for the top construction, I think I would be inclined to go for a box type setup as suggested by Señor Stick. That helps keep the table flat and you can use considerably thinner wood for the top without it being obvious.
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post #8 of 24 (permalink) Old 01-17-2017, 07:17 AM
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4x4's. It's all clamped together. And it turned out good.
I saw the 4x4s for the glue up - I meant, after it was done and the table was put together, but Charles answered that with the suggestion for saw kerfs on the underside.

@Cherryville Chuck

Charles - for smaller tables I've used figure 8 fasteners that allow for movement as well - I buy mine from Lee Valley but I'm sure they're available at other places.

Figure Eight Connectors - Lee Valley Tools
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post #9 of 24 (permalink) Old 01-17-2017, 08:42 AM
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MT Stringer, you have come through again for me! First the adjustable table and now this advice on a table top. Starting on the table for SWMBO real soon. First the planing and cutting to size. Your advice gives me some direction as how to do it.
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post #10 of 24 (permalink) Old 01-17-2017, 08:48 AM
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Originally Posted by Cherryville Chuck View Post

I would personally avoid having the legs go through the top. I would want a member between the legs cross ways for support, otherwise you are depending on glued butt joints to hold the weight up and the cross member wouldn't allow for expansion and contraction. Maybe someone elses experiences are different than mine though.
could faux the leg thru the top look...
edge spline the boards together for a major plus....

This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

Stick....
Forget the primal scream, just ROAR!!!
"SNORK Mountain Congressional Library and Taxidermy”
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