Beam deflection calculation frustration
So this should be simple. I know it should be simple. However, after getting WILDLY different answers on several online calculators, and doing the calculations "the old fashioned way" several times but feeling like the number is just too small, I turn to you for validation and 2nd, 3rd, 4th opinions. Here is my method and numbers, please let me know if anything jumps out at you as flawed. Thanks in advance for your help!
Length: 117"
2" square steel tube with .125" thick walls (a=2, b=2-(2*.125)=1.75)
Total Weight= 29.7375 lbs (per Ryerson.com stock list, also verified manually)
Deflection formula for simply supported beam with distributed load (machinery's handbook): (5/384)*((WL^3)/(EI))
W= 29.7375 (see above)
L=117 (see above)
E=Modulus of Elasticity=29*10^6
I=Moment of Inertia (machinery handbook)=(a^4-b^4)/12=(2^4-1.75^4)/12=.551757
Soooo... (5/384)((29.7375*117^3)/(29*10^6*.551757)= .038755, max rate of deflection in center.
Also got mixed results using online calculator on a round shaft of outer diameter 1.5, inner 1.25- same length.