1. ## beam

I was trying to calculate the deflection of a steel tube at engineers edge and some of their calculators are not working properly.
Here is the specs:A-36 hot rolled,12"X4"X.25X7'long simple supports.Center load
200lbs.I came up with a deflection of .000598.Is this correct?
Should the weight of the beam be in the equation?
Is there any other beam calculators on the web
Thanks
Larry

2. Hi,
I plugged in some numbers, and got 0.000622", the variation might be in the E(i used 30,000,000) and I(i calculated 132.4in^4). (assuming 12x4 rectangular tube with 1/4"wall, the 12" is vertical)

To take into account beam weight, its cross section is 7.75in^2, density is 0.284Lbs/cu.in, its weight is 2.2Lbs/in.
Now go into the uniform loading calculator, it says 0 deflection, i calculate it on my own, its 0.0000042"

I'm pretty sure these deflections can be added (please verify), but deflection due to beam weight is so small it can be negated.

Cheers, Dave

3. Get a copy of (free) beamboy: http://www.geocities.com/richgetze/ and it will do the calcs for you.

Ken

4. Thanks Dave,welcome to the ZONE.
I used Ix at19.9.
.0006 is good enough for a wood router gantry,if not overkill.Actually I rounded off the numbers for worst case.The beam is 74" with 12"x4" uprights,8" from the ends.The Z Axis will probably max out at 100lbs.The main reason for a tall beam was to spread the Y rails as much as possible.
Larry

5. One last thought, if you are using the beam with the 4" side vertical then the lower I value gives a deflection of roughly 0.004", which is still pretty good for a router.

p.s. thanks for he warm welcome

6. Originally Posted by lgalla
Thanks Dave,welcome to the ZONE.
I used Ix at19.9.
.0006 is good enough for a wood router gantry,if not overkill.Actually I rounded off the numbers for worst case.The beam is 74" with 12"x4" uprights,8" from the ends.The Z Axis will probably max out at 100lbs.The main reason for a tall beam was to spread the Y rails as much as possible.
Larry
According to the Solidworks beam calculator, a 12x4x0.25 steel tube has an Ix of 127.000 in^4.

Also, if you change the simple supports to rigid supports, deflection is reduced by 75% I think.

7. a question about gantry beam deflection I have been pondering lately....

why is beam deflection important? I mean, weight or load is never gonna change, so any deflection doesnt matter since the tool will always stay at the same spot.... any input?

8. Originally Posted by Gizmot
a question about gantry beam deflection I have been pondering lately....

why is beam deflection important? I mean, weight or load is never gonna change, so any deflection doesnt matter since the tool will always stay at the same spot.... any input?

ok... found it