homemade gantry crane advice

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I have been toying with building a rather small gantry crane. dimensions would be 4' wide and minimum height would be 7' for moving things in, out and around the garage. I'm quite short on cash so I have been thinking about what I have in the shop to make it. I'm considering using some 6" 3/8" steel flat bar 4' lengths to make a I beam. i would cut a piece of flat bar in half to have 2 3" pieces for the top and bottom of the beam and then welding it together. My posts would be from some 2"x2" 3/16" i have hanging around and i happen to have some 1-5/8" 1/8" round tube that i could use to make the height adjustable.I'm sure that the material selection would be good for light loads around 500lbs which is probably mostly what the crane would mostly see. I was hoping to be able to left my mill which weighs 1200lbs. thought i would check and see what people think about it on here
Reply:Do you have a sketch?
Reply:For the 500# lifting I would suggest getting an engine hoist. The collapsable ones stow away nicely, but I wouldn't want to be moving your mill around with it. Otherwise you should wait until you can get the proper materials. Those left over materials that  you have laying around  won't be sufficient to build a hoist large enough or strong enough to be of any practical use later on. It should be wide enough to straddle a trailer at least. The adjustable height feature is a good idea for a shop where you have low doorways, but you need to use square tubing for your telescoping uprights, and go bigger there as well.Good luck!
Reply:Trial ran out on my inventor so while im waiting to activate it i roughed you a sketch in paint.http://i80.photobucket.com/albums/j1...r/untitled.jpgI would get an engine hoist but i have no room for one, and they require a good bit of space when moving items which i don't have. The thought with my small crane would be I would be able to move it through the paths in the shop easier than an engine hoist and could store it in a walk way virtually taking up no room since you would just walk through it. not to concerned with making it so a trailer fit in it. since i don't have a trailer or even a vehicle with a hitch. for what it is worth i did a stress analysis on what i had designed and with 2000#s the was .005" deflection. Thought id ask others since i am self taught on the program so im sure there are some things i messed on setting up the analysis so not sure how accurate that number is