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(12-12-2019, 12:27 PM)ed kerns Wrote: ...I'm thinking of using some angle iron screwed to the bottom to make sure the top stays flat...Does this sound like a reasonable method to you all?...
No.
Angle iron is a very poor shape for use as a beam. Square or rectangular tube would be much better.
Wood is good.
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(12-12-2019, 12:27 PM)ed kerns Wrote: I'm looking for some advice on a project. I am building a desk top of 3/4 hickory and plan to build up the edges so on profile it looks thicker. This is a big top, about 32" X 72". The boards are flat as opposed to on edge in a butcher block style, so I know wood movement will be considerable along the width. In addition, a cabinet will sit under each end, but about 36" in the middle will be unsupported. I'm thinking of using some angle iron screwed to the bottom to make sure the top stays flat. I would over-size the holes to allow for wood movement and the steel would be hidden by the built up edge of the top. Does this sound like a reasonable method to you all? I'd prefer a more elegant approach, but the really important thing is that the top doesn't twist or warp. Thanks!
I'm no expert, but have you considered bread board ends with battens in the middle? I've done this with a similar sized table top - bread boards were pretty standard and the battens were set into a sliding dovetail that ran the width of the top. The table has been in service for 6 years or so and so far has shown no indication of going out of flat. Alternatively, could you use table top buttons to fasten the top to the cabinet sides to stabilize the top?
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I don't think it's necessary. Fine Woodworking covers this occasionally. I think I would use figure 8 fasteners
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Thanks guys, I appreciate your input. I suspect you're correct that the top will stay flat on its own, but really just looking for some insurance. I like the breadboard end idea and will consider that. I respectfully disagree on the angle iron profile not being strong enough, but agree that a 'U' channel or tube would be even stronger. For some years I built picnic tables out of pressure treated lumber which of course wants to go in all directions as it dries. We would sometimes use angle iron on the bottom side to hold the top flat. Not pretty, but it works.
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I think angle iron is too strong. I would do something to keep it flat, but if you constrain something too much you will have problems. Wood needs to be able to move, but you can guide it.
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The cabinets should keep it flat if you use table top fasteners to secure it to them. If you are worried about the center section use a wood batten underneath, with slotted holes as you move away from center. Nothing wrong with angle iron, just looks ugly to me.
In any case, make sure you finish the bottom of the table, too, so the moisture exchange is consistent with the top.
John
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"angle iron" comes in many sizes so picking right size will make a big difference.
I've used "unequal leg" angle in places where I needed more rigidity in one direction than the other.
For example a 1" x 1-1/2" x 1/8" angle would work well for a brace without significant weight (compared to the 2"x2"x1/4" I use for welding tables)
If you attach it to the middle and the ends of the top are not constrained it might work, but if the boards are only 3/4" thick it will be difficult to take advantage of the strength of the steel
A good wood brace might be more practical.
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(12-12-2019, 12:27 PM)ed kerns Wrote: I'm looking for some advice on a project. I am building a desk top of 3/4 hickory and plan to build up the edges so on profile it looks thicker. This is a big top, about 32" X 72". The boards are flat as opposed to on edge in a butcher block style, so I know wood movement will be considerable along the width. In addition, a cabinet will sit under each end, but about 36" in the middle will be unsupported. I'm thinking of using some angle iron screwed to the bottom to make sure the top stays flat. I would over-size the holes to allow for wood movement and the steel would be hidden by the built up edge of the top. Does this sound like a reasonable method to you all? I'd prefer a more elegant approach, but the really important thing is that the top doesn't twist or warp. Thanks!
Use Plywood. Build up however much you'd like, use solid edging. Problem solved.
