Simple Scissor Jack calculations

[mike009]

Hello every body,

I have been searching for Scissor jack “mechanics and mathematical” calculation for ages
I hope I can find the answer here.

I have some knowledge about statics and dynamics.
Can you please help me with the calculation of the Scissor jack “statics and dynamic”, or the place to find good information about how to calculate

Here are the properties of the Scissor jack,

Max lifting weight = 1000 kg
Max height = 325 mm
Min height = 90 mm
Weight = 2 kg
Pitch = 3 mm

Thank you in advance

 

[GregLocock]

"I have some knowledge about statics and dynamics."

but not enough

you are missing at least one dimension.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[mike009]

Hello GregLocock,

I'm missing one dimension?
are you asking if the calculation will be in 2d or 3d "statics" and oneD and 2D "dynamics?

I don't really understand what you are talking about!!
what is not enough? my knowleadge of statics and dynamics?
sure i have knowleadge but i'm not an expert, that's why i'm asking your help.
this is not homework or project or what ever, i just want to learn how to calculate forces and power or what ever possible calculation on this machine.

thanks in advance

 

[JStephen]

Statics and Strength of Materials should pretty well cover the analysis.

For info on screw threads, you might check the mechanical engineering handbooks.

As to calculating the allowable load in the different parts- you might try the latest AISC code, which I think can be downloaded free. It has strength equations for flat bar turned on edge, which would cover the scissor jack I have.

 

[IRstuff]

The missing dimension appears to be the dimensions of the jack itself.

Is this for school?

TTFN

FAQ731-376

 

[mike009]

no its not for school,
I'm programmer and i need the calculation to help me to develop some functions.

I did mechanics in schools, but i really don't remember any thing about "missing dimension"

 

[hydtools]

Try this:

http://www.engineersedge.com/mechanics_machines/scissor-lift.htm

Ted

 

[zekeman]

"Can you please help me with the calculation of the Scissor jack “statics and dynamic”, or the place to find good information about how to calculate"

Mike,

Why don't you post or otherwise indicate the dimensions of the scissors and the configuration at the minimum height.
What you are asking in general, is very simple but you can't get answers without dimensions.

 

[mike009]

Thank you all guys for the help,

still don't get "indicate the dimensions"?

Okey, lets try this,
it's 2d calculation in static position in max height"325 mm" and max load "1000 kg" pitch = 3mm

is this what you mean? if not please tell me what do you mean by indicate the dimension?

 

[GregLocock]

One candidate for the missing dimension is the length of the screw when fully extended or fully retracted (clue, it won't be zero).

Then draw a free body diagram of each element in the mechanism, assuming symmetry. You may need to use he principle of virtual work, or a real work equation. By eye the thing is not overconstrained, it should be fairly easy.

Then analyse each part for strength etc.




Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[MikeHalloran]

The relation between screw motion and jack height is not linear, because of the triangles involved, and the way their geometry changes as the jack moves.

You have to model that geometry.





Mike Halloran
Pembroke Pines, FL, USA

 

[Farmboy71]

Also, you can have the actuator push directly on the center pin. I think this is pretty common in scissor lifts.