Where can I find rating to figure out what size of I beam I need for a given span at a given load?
I am planning on building a 2 ton A Frame type gantry crane. 8' max span. Chainfall hoist.
I'll check my thrift store books if nobody else chimes in. They have tables where you just select the beam size and look across the chart for the load capacity.
had a look around in work, found a lifting beam about 8' long, simply supported marked SWL 2 tons, it was about 8" deep, 5" wide and bout 1/2" thick, it had a sliding runner on it.
That was a useful site. I've added it to my bookmarks. Thanks for the pointer
Too bad they want at least $6 a month.
The approach I took was very simple. Take a look at any catalog or campany web site that sells them like Gantry Catalog
Most show the dimension of the products they sell. Given the 8' span and 2 ton capacity, the beam section used here is an 8" tall x 4" flange S type beam weighing 18.4 lbs/ft. Keep in mind that a crane is ultimately designed for stiffness not strength. If you design the structure for strength, you can wind up with a very flexible crane. Also make sure the casters are rated for the appropriate load.
"Keep in mind that a crane is ultimately designed for stiffness not strength. If you design the structure for strength, you can wind up with a very flexible crane. Also make sure the casters are rated for the appropriate load. "
And GOOD casters are not cheap.
From what I have seen in homemade cranes, the casters are almost always undersized and underrated. Roll the crane while carrying maximum load and a caster will separate...CRASH.
Simple beam calculations do not take beam roll into account and if you make the beam too long, your beam will fail, regardless of the simple beam calculations. If you look at the gantry crane site provided in a previous post, you will see in the first picture, a long beam reinforced along the top flange. That being said, given the length you have expressed a desire to build, you should be OK with the beam shown. If you use simple beam calculations to size things, use appropiate safety factors. Where I work, we use ultimate safety factors of 3 for standard structures, and 5 if people are at hazard. Assume A36 material specifications for your beam.
TMT said: "And GOOD casters are not cheap." Amen. Worst case; figure 50% of the manufacturer's load rating.
You will not get good casters from the home center nor good advise from a min wage shelf stocker. Consult a reputable caster supplier. Be sure he knows the full application you intend for the caster.
While ductile iron wheels are strongest they are hard on smooth concrete floors. They crush the surface over time and expose the aggregate.
Use phenolic wheels for easy rolling when loaded and double ball swivels for maneuvering. Phenolic wheels while not as free rolling as ductile iron will give you better service and are easier on the floors. Do not consider rubber or urethane wheels for heavy loads to be hand manipulated. They are kind to floors and roll very smoothly but require too much muscle.
Consider position stops on the caster swivels so you can lock the direction of one or more casters. You'll love them when moving a loaded crane along a restricted path.
Macona, My 20th Edition of Machinery's Handbook has considerable detail regarding beams, deflection and calculations.
I agree with Mr Addy, casters are the weakest part of a gantry. That's why I built four of these for my gantry:
Thrust bearings are surplus throw-out bearings. Wheels are 10" dia.
Also Mr Addy's suggestion about setting up a positional locking system for each caster is a valuable feature, especially if you are working on uneven surfaces. In fact, setting mine up with such a feature is on my list of things I better get done. WWQ
Another movable gantry has been on "to do" list for some time.
In addition to making the heights adjustable I am currenlty planning on including a short built-in screw "jack" by the casters. This will allow me to increase the load when stationary, and if set close to the ground when moving with a load would reduce the "drop" on that section should a caster fail.
I have also thought about having each of the 4 corner end in a short "T" and have a pair of casters to share the load instead of just one.
If you knew it would only be used on a flat surface you could add in a third caster which would only start to bear when the structure was nearing- say 2/3 of the designed maxium load. My inital thought was this could be done with beam bending- but it might be better done with bellview washers. Hummm...the bellview washers would also allow load sharing with two casters on one end beam without the "T" on the end. Back to the drawing board...
What ever you do add two trolleys and hoist. Makes it alot easier to pick up some things. I think the simple beam calculations should be fine for 8'. As said before you can not get heavy enough casters. Using them is pairs is a very good idea. They will all load equal on a half way flat surface because the beam and frame will twist alittle.
JR you can come see mine sometime. This is a pic of it my shop is right outside Columbia.
Good comments Forrest.
I also figure 25-50% of a rated caster...as has been mentioned the caster is the weakest link in a gantry crane.
Lifting devices tend to be abused and asked to lift more than what they are rated...better to overrate all components.
I look at the casters on the Asian engine cranes and just shake my head....I wonder how many people have been hurt by their failures.
Went up to Seattle yesterday to go to Boeing Surplus and while I was there checked for casters. Lots of nice caster just no 4 of any one kind. Well, actually there were but the one that they had 4 of were about 15" dia wheels! I would need the crane just to move these casters.
So now I am looking for a chunk of I beam. My dad is checking with a couple of his friends if not I think I can get a piece from craigslist.