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Table top sag calculation

5/29/19       
Chris

Gentle ben,
We are building a table 42" W x 116" L as seen in link below.
Top: 1 1/2" lightweight MDF w/ 1/4" thick x 1 1/2" wide solid RIFT WOAK banding then veneered both sides in RIFT WOAK.
Question is what size metal and what shape to keep table deflecting for normal use.
Thanks


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5/29/19       #2: Table top sag calculation ...
duster

Unless this table will be doubling as a dance floor, what you've spec'd in your drawing should more than adequate. I'd make those aprons at least 1" thick so you can get good purchase when you screw through the steel.

5/30/19       #3: Table top sag calculation ...
Josh Koschak

Also, Id use cold rolled angle vs hot rolled.
Its straighter to begin with and has a much crisper look to it, along with increased strength properties.

5/30/19       #4: Table top sag calculation ...
David R Sochar Member

Why do you need steel?

If you think the table inadequate in support, add one or two 5/4 thick x 3" or more down the center from rail to rail, no breaks.

My first thought when I see steel added in where it is not needed is that a novice did not have any knowledge he could trust.

I prefer dancing on tables with a solid wooden response. I'd let duster go first, though.

5/30/19       #5: Table top sag calculation ...
Chris

Thanks all. I was wondering when you’d show up David. For the record, I’ve been at this for 25 years now so certainly not a novice but definitely not an engineer.
We’ll build the thing and see what the deflection is and then decide.
Thanks again for your responses

6/2/19       #6: Table top sag calculation ...
David R Sochar Member

MDF as we all know, likes to sag. It has a hard time supporting itself. So you can't count on it to help with things.

Wood may sag under enough weight, but readily springs back, therefore lending to your solution. Adding wood - beefier cross section- adds to its ability to stay straight. I also am no engineer, but I do know that I prefer a wooden solution.

6/10/19       #7: Table top sag calculation ...
Bruce H

Why not build it as a torsion box? It would self support without issue.

6/11/19       #8: Table top sag calculation ...
Chris

Thanks Bruce. Because they want it to feel like solid.

6/22/19       #9: Table top sag calculation ...
Karel Brouwers

Hello,
I think you will find that square tube will be stiffer in bending than angle bar. I agree with David to increase the thickness of your side rails. You need to drill a hole the head of the screw can pass through in the first wall of the tube and have the screw act on the wall of the tube contacting the side rail glue in the joint would not hurt either. Use a heavier wall tube a rectangular section if available on edge. I am also not a fan of MDF. Perhaps attach some cross braces underneath also. It is good to veneer the bottom of your top to have balanced construction. You could also make the side rails torsion boxes and not need the steel. Good luck. karel


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