Lift Table Project Question

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I am trying to put together ideas for making a lift table. It would be alot easier to work on mowers and motors three feet off the ground. I know I could buy one at HF for under $100 but making it is half the fun. I have been looking at some ,and a single sissor design would probably work. 500lb capacity would be enough. I would like to use a pneumatic cylinder with a lever operated ball valve to control flow. When looking at the hydraulic tables there seems to be a whole lot of lift for little piston stroke = more power needed. Could I get this from air and what size would I need? Any ideas on this project would be helpful. Thanks
Reply:Harbor freight has those long air operated cylinders used for engine hoists.  Might be just the ticket.DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:the closer the piston is to the fulcrum/pivot point, the greater the required energy/power to acheive the desired result. i'm not sure how quickly you would want the table to move, but i know you can get a car jack and rip the cylinder out of it. i also have seen truck jacks (semi-trucks that is) that are air powered and rated for well over 50 tons. i think that should do just fine for you.  As far as exactly sizing one, i'm sure that you could find an equation somewhere, but even as an engineer-in-training, i can tell you that the bigger you go, the safer it will be. as far as i'm concerned, you never can have too much power. if all you are looking at trying to lift is 500 pounds, try to make it rated for 1000, just to be safe, and throw on a 2.5 or 3 ton car jack cylinder. i know Wal-Mart sells them for about 30 or 40 bucks, including jack stands (at the worst, these can be used for scrap). i would reccomend making your top out of at LEAST 1/8" (for a wear-and-tear margin), preferably 3/16 or 1/4, and your scissor legs to be at least 3/8 think by 1 1/2" wide. as far as the base, i would use 2" x 2" x 3/8" angle stock and throw in a few cross-braces to triangluate things as best as possible. one thing that i have noticed from people trying to design things like this is that they do not account for lateral motion, only vertical. they concentrate on getting the biggest load possible into the air, but don't think about what can happen if someone knocks over the load. also, i woudl highly reccomnd setting up some kind of mechaincal safety system. if, for any given reason, you try to use the table and it is either over-loaded or the piston decides to fail for some unknown reason, the mechaincal brace will support the load and safe toes, fingers, cords, etc. from being severed. this can be as simple as a support point on one leg and another connection point on the bottom of the table with a bar in between, all the way to a ratcheting system (automatic safety... used on car lifts [not jacks]). heck, you could even just pile up as many 2X4's as possible under the table. simple, yet functional and safe. let me know if you want some more definate/detailed measurements and/or plans. i love doing little profjects like that on CAD.later,AndyLast edited by aczeller; 10-18-2007 at 02:24 AM.
Reply:Good thought on the safety aspect. I figured i would make it so there was a place I could insert a safety pin when in the raised position. Could a hydraulic cylinder work with air? I remember my father checking them with air pressure.
Reply:Originally Posted by ronboCould a hydraulic cylinder work with air?
Reply:Originally Posted by ronboI am trying to put together ideas for making a lift table......I would like to use a pneumatic cylinder... ...When looking at the hydraulic tables there seems to be a whole lot of    lift for little piston stroke = more power needed... ...Could I get this from air and what size would I need? Any ideas on this project would be helpful. Thanks
Reply:I may be taking this in a different direction. While digging in the shed I found one of those old tripod, crank top, bumper jacks. It has about a 1" diameter acme threaded shaft. I could put a nut on the end and run it with a reversible impact wrench. I would think this was probably originally designed to lift over 2000lbs so that shouldn't be a problem. Any thoughts?(My luck I'll tear this apart and find out I could have sold it on e-bay to a car restorer for $200. HA
Reply:i would say go for it, as long as you think it's structurally sound enough to hold it, and your impact gun is strong enough to move the nut. it would be a mechanical piece, so it woudl act as it's own locking mechanism. the only way i could see anything going wrong woudl be if the threads completely strip out, all at once, which won't happen. the table would break and the gun wouldn't spin the nut if that big of a load was on it. IMO, try it. test it in a controlled situation, where no one can get hurt if it fails, and worst case scenario, you hack it off and try something else.later,Andy