How to reduce deflection on this DIY table.

[andrew_barrios]

I've gone and made an attempt at building a height adjustable table (think ironing board). Originally I was going to use stainless steel for the pipe, but after finding out that it would more than quadruple the price, I ended up with SCH40 Aluminum. I used three 48" long, 1" ID pipe for the legs which criss-cross and attached them to two 36" long, 1.25" ID feet.

I put it all together and mocked up a table top and everything works great.... Then I added some weight to it do simulate the weight of the actual top I plan to use (70lbs) and the pipes start to flex and it makes the whole thing kind of springy. If you set a glass of water on top you can see the water moving back and forth as the table bounces (jiggles?) until it finally settles and stops.

I'd attach pictures, but I don't see that option. Here's a link to a video that has a similar table design and operation.
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Is there any way to stiffen this thing up enough to make it more solid? I thought about drilling into the long pipes and filling them with concrete, but what happens when that starts to crack? I also thought of cutting the welds and inserting 1" solid steel rod (or flat steel oriented vertically) into the pipes. Or there's always the option to add pipe.

Would any of these options work? Any other ideas? Or am I out $100 and need to redo this with larger diameter steel?

[Kelly_Bramble]

You have an iron board... Sure, fill it with concrete though weight will increase. Be sure you have plenty footing that is wide.

iron-board.jpg

[jboggs]

Actually I think filling with concrete might make things worse. The concrete will add a little stiffness (maybe) but will also add a lot of weight. The actual load on the legs is a bending load, and concrete is not real good under bending loads. There are ways you can attach an image. Try again.

[Kelly_Bramble]

So, concrete is great in compression and poor in tension. Which is why concrete includes steel rebar located towards the tension side in pavement.

The op could fill the tubes with wood or another materials good in both tension and compression.