Screw Jack Design

Screw Jack DesignThe Three PandyasChristian Grady, Kunind, Diana Paek

Overview Identification of Need Research Standard and codes Bill of material Design Calculations Components Material Selection Stress Concentrations Conclusion

What is a Screw jack?

A screwjack is a mechanism that converts rotational motion to linear motion, and a torque (rotational force) to a linear force.

They are mainly used to lift heavy weights.

Identification of Need A local car company contracted out The Three Pandyas’

design group to design a screw jack, which can hold up to three tons of weight.

The screw jack needed to be safe, easily operable, and cost efficient.

The Three Pandyas determined that this particular screw jack design would need to include five parts.

These five parts were: the bottom frame, the threaded screw, a nut, a handle, and a cup which sits on top of the screw and holds the car up.

Research A screw jack is a device used to raise or lower a load, and can be utilized

in numerous applications, and modified to lift various shapes of materials.

There are two types of screw jacks that are generally used. The first type is a mechanical screw jack,

operated by hand with an attached handle, or power driven using some form of a motor and belt or gear

system. Car jacks are usually designed to harness a mechanical

advantage in order to allow for a human to lift the car. The second type is a hydraulic screw jack.

More powerful than most mechanical jacks Operated through a cylinder piston mechanism. They are used to provide more lift over a larger distance

Standards and Safety Factor Regulations Placed by OSHA Safety factor of 2 was chosen to ensure the safety

of the design Shoulder width of 120 inches is available according

to interstate Highway Standards

Bill of Material

Component Number

Component Name

Quantity Needed

Material Choice

1 Screw 1 Low Alloy Steel (Grade count: 1579)

2 Nut 1 Phosphor Bronze (Grade 1_IS: 28-1975)

3 Handle 14 Frame 15 Cup 1

Design Components (AutoCAD)Screw

Nut

Design Components (AutoCAD)Handle

Frame

Design Components (AutoCAD)

CUP

Material Selection Power Screw, Handle, Cup, Frame

Low alloy steel Torsional, bending and axial load Strength was the priority

Nut Phosphor Bronze

Reduce friction resistance b/w the screw and the nut Softer material Lowers heat and other energy loss

Final Design SpecsSpec One Start Thread Two Start ThreadLead 0.125 in2 0.25 in2

Torque Required to Raise Load

826.94 lb-in 848.866 lb-in

Torque Required to Lower Load

287.72 lb-in 309.852 lb-in

Length of Handle 19.045 in 24 inForce on the Handle

89 lb 72 lb

Diameter of Handle

0.547 in 0.551 in

Mechanical Advantage

147 183

Stress Concentrations Maximum at the sharp corners Stress due to bending Stress due to bending and torsional

moment Eliminated the chance of buckling or

crushing by keeping the screw short.

Failure Analysis

Load not properly secured Slipping or tipping

Improperly Assembled Centre of the gravity of the jack is off

Not placed on a hard and a leveled surface

Conclusion

Analytical procedure detailed in the class was used to come up with the design of the screw jack.

5/8” acme power screw was decided to be used. Improvement

Thread Start changed from one to two, allowing the same load (6ton) to be lifted in shorter amount of time.

Length of the handle had to be increased in order to apply even less amount of force keeping the torque applied on the screw to be the same.