[Zumba]

Walter
Here is a good question for the engineering members.
If you fill say for example an A-36 4"X4"X1/4" tube withE/G,Will it be stiffer or will the added weight cause more deflection.
Larry

Yes and yes.

It will be stiffer in that it will be less prone to deflection under cutting forces.

However, it will also deflect more while the machine is at rest, under gravitational forces. But we're talking tenths at the most. A 4"x4"x.25" x 48"L steel tube deflects .00024" under its own weight in a horizontal position (load at the center of the beam). A 3.5" x 3.5" x 48" solid E/G bar deflects .00033" under its own weight. Add the two together and you end up with something in the middle.

However, the important thing here is the 48"L. In the beam deflection equations, the length is cubed. So double your length, and you increase your deflection by 8 times. The weight of the E/G becomes an issue at this point.

So let's say you want a 16 foot beam. You can't use a 4" x 4" cross section for this. Without center support, this sucker will deflect over SIXTY FOUR TIMES as much as the 4-foot beam. That's around 0.019. That's with NO LOAD!

EDIT: actually that's an underestimate... I increased the length but didn't take into account the 4x weight increase! So we're talking more like .080.

So to fight the gravitational force, you'll have to increase the height of your beam. 8" high will decrease deflection to about 0.010 (and I again, I haven't taken into account the the added weight of the E/G). Still not great. I'd recommend adding at least one center support, preferably more. Either that, or go real big with your tubes.

And don't fill up completely with E/G unless you have to!