steel vs al cantilever
steel vs al cantilever
(OP)
I'm comparing the merits of using steel versus aluminum for an L-bracket. It is to be mounted on a motorized turntable oriented perpendicular to the ground. It'll be about 5' x 6' & have about 300 lbs at the end. Although I can use cntr-weight, I prefer to minimize it. Deflection is my main concern. I'm looking for rules of thumb based on trends I see. Can anyone confirm?
1) For a given cross-section, AL & steel cantilevered beams deflect about the same under their own weight, so AL is more attractive due to its light weight (ignoring thermal props, etc.)
2) Steel begins to look more attractive when there is a load at the end. Looking at square tubing; for a given load, in order to get the same deflection from the AL, the "I" must be increased so as to make the weight of the AL approach that of the steel (this assumes wall thickness can be increased but tube O.D. can't).
In my case since I have an L-bracket, I'm thinking that the part that is perpendicular to ground should be steel & the other leg I'm still debating.
Thanks, vbk
1) For a given cross-section, AL & steel cantilevered beams deflect about the same under their own weight, so AL is more attractive due to its light weight (ignoring thermal props, etc.)
2) Steel begins to look more attractive when there is a load at the end. Looking at square tubing; for a given load, in order to get the same deflection from the AL, the "I" must be increased so as to make the weight of the AL approach that of the steel (this assumes wall thickness can be increased but tube O.D. can't).
In my case since I have an L-bracket, I'm thinking that the part that is perpendicular to ground should be steel & the other leg I'm still debating.
Thanks, vbk





RE: steel vs al cantilever
2) Steel looks more attractive for the same shape. For very thin hollow tubes (t<<d), you are correct that aluminum and steel would give eqivalent stiffness/mass performance for the same OD. However, if the OD can be increased, aluminum can be significantly superior to steel (as Ixx will increase much faster than mass).
Brad
RE: steel vs al cantilever
Above are just a few thoughts on issues to consider. Sorry no definitive answers!
Mike
RE: steel vs al cantilever
Since this is an antenna measurement application & geometric bulk is undesirable, I'm leaning toward steel, at least for the vertical section. We've made variations on this in the past with heavier & lighter loads. Typically we use sandwich type steel construction with channels or I-beams welded inside of plates. It isn't a static load. It travels in Elevation (as opposed to Azimuth). As for fab processes, I guess for large welded structures steel is preferrable.
vbk
RE: steel vs al cantilever
Although aluminum looks nice,
Steel rules.
RE: steel vs al cantilever
RE: steel vs al cantilever
It appears that you have quite a few good leads and comments with the previous threads.
Have a great weekend,
Jay
RE: steel vs al cantilever