Howdy. I'm looking into building a frame made of equal leg angle to put a tall 19" rack on wheels.
Do you know of a formula that yields the minimum size of the angle for a given load and span ? Not the full blown one for structural engineers, I wouldn't understand it ; just a basic rule of thumb.
Thanks in advance.
I suggest you explain more in details what you are really trying to do. Many shapes could still possibly form equal leg angles. What is a 19" rack on wheels??? A good specific question could normally generate good specific answers. Conversely, vague situations could lead one into vague assumptions.
a 19" rack is a standard sized computer rack that one slides boards or entire computers into.
How tall is the "rack", they come in 30 inch tall to 11 feet tall. I think yours is a common 6 feet tall unit.
Bill K7NOM
If you can't design a structure properly, normally you heavily over- design it. In this case the load is in the corners, right? so the off- center support of swivel casters will twist the angle, especially if you roll the rack into a power cord or door sill.
One simple way to make a caster base from angle is to connect each pair of casters with two lengths of angle, one on each side, facing down and separated by the longer dimension of the caster plate so they don't hit the wheels. Then connect the two subassemblies with one piece on each side, facing up to keep the load from sliding. The four caster plate bolts hold it all together without welding.
jsw
Note that I suspect that the original posting is a troll. Look at the e-mail address, not the user name in quotes.
A '19" rack' is a frame for supporting electronic equipment with front panels 19" wide, and several possible panel heights in integer multiples of 1-3/4".
The front rails are drilled and tapped (or designed to accept clip-in nuts) at varying spacings which all work out for the standard rack panel definitions. If drilled and tapped, the most common thread in my experience is #10-32, but #12-24 are also sometimes used for heavier loads. It is this variation which makes the clip-in nuts in plain holes more attractive to manufacturers.
The equipment *may* be supported purely by the front panel ears (the space between the front rails is 17-1/2" IIRC), or may be supported by side slides which are attached at both the front and the back to the vertical rails.
The simplest ones are simply a base plate and a frame providing the front rails only (open frame rack). The better ones have side panels, rear doors, and some even have front doors.
The weight of an individual item could vary from perhaps a couple of pounds for a 1-3/4" high module which extends only a short distance back, to something which might weigh as much as 300 pounds for a single 10-1/2" high module. And this module can be anywhere from near the bottom (which is what would make sense for that heavy a module) to near the top. And the taller racks have 72" of panel height, so you could easily have 1800 pounds in a single rack.
If 1800 pounds, this means a bit more care in selecting the casters as well.
I *think* that what he is asking for is a frame made of angle into which to drop an existing rack, instead of using the usual hard points on the bottom designed for attaching casters.
A good rack will have jack screws at the corners which can be lowered into contact with the floor once it is in the right position, thus taking the load off the casters, and also have slide-out legs at floor level to keep the rack from tipping forward when one or more of the modules is pulled forward on its slides for access. Both my 72" high Sun rack and my 40" high DEC rack have such braces and jack screws.
They typically don't have diagonals at the sides, so equal-leg angle would not suffice with a load such as that unless it had very long legs. The side panels are sometimes attached by screws so they can offer some resistance to parallelogram buckling, but they also are sometimes left off, or just rested in place on hooks for easy access.
Front-to-back dimensions also vary, My tall one full of various vintage Sun computers is 36" front to back, and a shorter one (made by/for DEC) is 24" front to back.
Even knowing what a 19" rack is does not give anywhere near sufficient information to answer his question. Some clues as to what size modules (panel height, front-to-back length, weight, whether they are supported only at the front or on slide rails supporting at both front and back) will give some improved chances. How many of these modules, etc, etc.
Good Luck, DoN.
Well, I would like to keep it vague for the moment because I'm looking for a general answer.
Suppose you have a piece of equal leg angle steel that is somehow rigidly maintained in this position :
______ | ____| ^ | / | S | | | |_| v
TThis beam is set on thin supports at both ends. A load is placed in the middle.
M | | ____________________v___________________ v | | | S |________________________________________| | ^ ^ ^ |
I'm looking for a formula that links L, M, S and T, assuming the angle is made of ordinary hot rolled steel.
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