scissor lift design

By no electrical, you mean no motor and reduction/chain/cable system? Both hydraulics and lead screws have motors which need plugging in, unless your talking about squirrels on a running wheel.

By the way, there maybe more to just lifting a 16½ ft² 400# load up 7'. Worker interface, safety, local and state building approval codes, controls, maintenance, installation issues might determine that simple little design. Just something to think about.

Keith

Any reason you can't just buy one of the myriad of lifts on the market?

Like I said no electrical power, will be using hand pump for the hydraulic and hand crank for the lead screw. if possible

Each arm overall is 64" pin to pin is 61". it is two pairs , I have cad mock up of tow cylinders attached to base and then to second pair of arms, when folded the cyliders are at 9 degrees to horizontal, i calculate loading to 1917 lbs at thisposition so 958 per cylinders.

I am aware of codes that I can work within.

I did a scissors lift for a co-workers some years ago, to lift an ATV for maintenance. Worked slick but found a few caveats while and after building, there are unpredictable forces on the structure (more than up and down). It used a hydraulic jack but didn't have the platform height you are looking for.

Keith

Each arm overall is 64" pin to pin is 61". it is two pairs , I have cad mock up of tow cylinders attached to base and then to second pair of arms, when folded the cyliders are at 9 degrees to horizontal, i calculate loading to 1917 lbs at thisposition so 958 per cylinders.

I am aware of codes that I can work within.

Too bad it has to be a scissor lift. A good alternative off the top of my head would be a modified tool/die lift. They can lift that load to about that height, are stable and the manual ones are hydraulic foot pump type as well as having about the same foot print as a scissor lift would have....

IYM

Each arm overall is 64" pin to pin is 61". it is two pairs , I have cad mock up of tow cylinders attached to base and then to second pair of arms, when folded the cyliders are at 9 degrees to horizontal, i calculate loading to 1917 lbs at thisposition so 958 per cylinders.

I am aware of codes that I can work within.

Keith any pertinent info would be good though, i am needing some help with bearing /bushing selection and force calc .

If you have any pointers at all that would be good, for instance what kind of rollers did you use for arms or where they on guides? What kind of bearings will i need? etc

Thanks.

IYM,

Do you have anymore info on this? , I am open to suggestions.

The lift tables I was thinking about didn't quite get to the 7' you are looking for and maxed out at about 5 or 5-1/2'. However, I did find this one. One criteria you didn't mention was what you needed in a platform for it. This one I believe is a hand hydraulic pump, max height of 12', 500lb capacity and has base dimensions within your criteria (without outriggers, but I don't think they are required for a 7' lift)

Again, this isn't the original design I was thinking of, but it might be something to look at (without knowing what your lifting)

IYM

Do you have anymore info on this? , I am open to suggestions.

You might want to take a look at these also. I visited the manufacturing plant in Montreal, its an ingeniuos system. Very high lift to footprint ratio. These actuators were used to operate Celine Dions stage in Vegas and are used in the mining industry.

Oops forgot the link

scissorlift design is rather straight-forward and one of your classic statics problem (unless this lift will open to 7' in under a second)

there is a critical piece of info missing here and, if I were to guess, the crux of the problem: do you have a constraint on the closed height?

usually, the puzzle pieces look like this:

- load capacity

- table size

- open height

- closed height

you'll soon realize that you can't (easily) fix these independently (unless you're lucky with the numbers).

for example, your max lift height will be related to the table size (footprint) which in turn will dictate your closed height.

stacked scissors will get you higher, with a smaller footprint, but will make your closed height at least double.

for single scissors (double check this with some math) you should avoid pulling the moving leg (slot/roller) closer than 60% the length of your table.. unless you make an incredibly rigid table (ie heavy).

if you're going from 3.5' to 7', it won't be too hard (for example, the die-lifts as mentioned earlier, usually don't go lower than 24" or so)

also, be very cautious if you're working with a non-static load -- like a 400# work crew. keep a close eye on your center or gravity during the lift.

the 'hardest' work happens, of course, when you initially open your table.. lets say during that first

that said, most of these sorts of lifts employ bronze bushings (if anything at all )on the fixed sides (and center pin) and "cam followers" on the moving ends riding in a simple structural steel rail.

sorry so long-winded.

-Tony

one last tidbit you may find useful: have a look at WorkingModel by MSC.. they offer a demo version through their website (full featured with disabled "Save")

it will allow you to simulate the scissor lift with loads applied, allow you to monitor pin/element loads throughout the cycle and you'll be able to spot potential binding.

if you're familiar with current CAD software and your physics is still fresh, the learning curve is nothing.