Scissor Jack Design Project 566u6c

Scissor Jack Design Project GE 410 Fall 2005 Jim Ramirez David Hettinger

Instructor: Hall 12/05/2005 ii

ABSTRACT Scissor jacks are simple mechanisms used to drive large loads short distances. The power screw design of a common scissor jack reduces the amount of force required by the to drive the mechanism. Most scissor jacks are similar in design, consisting of four main driven by a power screw. In this report, a unique design of a scissor jack is proposed which is very easy to manufacture. Each member, including the power screw sleeves, is made of the common c-shape. This eliminates the need for machined power screw sleeves, which connect the four and the power screw together. The manufacturability of the proposed scissor jack lowers the cost of production.

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Calculations and Assumptions for Crank Handle…………………………… 17 Appendix H: ANSYS Force Analysis……………………………………………………... 18 iv Introduction The most basic scissor jack design is truly engineering at its finest. With the power to magnify input forces, scissor jacks allow us to raise vast loads using only a fraction of the force ordinarily needed. Our goal in this project is to design an efficient scissor jack capable of raising a 2000lb load. As a screw-driven mechanical system, the jack will be manually operated and have at least 7 inches under load. The design will be transportable and storable, have a removable crank handle, and operate with a factor of safety of n = 2 using standard mechanical design methods for all components. The design itself has gone through multiple stages of development. We have taken several possible failure modes into and are confident that our design is efficient and safe.

Proposed Design Summary The scissor jack design, shown in Figure 1, consists of four main lifting , four connection , a power screw and a crank. 1 through 8 are all primarily cshapes with ideal pin connections. 1 and 5 both have additional details to for the surfaces. The power screw is single threaded with a collar at the member 3 connection. All are 50 ksi strength steel with the exception of the rubber grip on the crank. The following is a summary of the design features for our proposed scissor jack. Details of the design specifications and failure criteria can be found in the attached appendices.

Main Lifting : These are made from simple c-shapes. The web of the is cut out near the pin connections to allow proper serviceability of the scissor jack at its maximum and minimum heights. 4 and 6 have ideal gear connections to balance the load between the left and right side. The flanges of the channels are to wrap around the flanges of the sleeve . The lifting are greater in length and are subjected to compression. Lifting member flanges on the outside of the sleeve flanges is to compensate for slenderness ratio by increasing the moment of inertia of the lifting . Sleeve : The sleeve channels are to open inwards as shown in Figure 2. This is so the flanges are subjected to tension instead of compression. The bending moment from the power screw creates tension on the inner edge of the sleeve and compression on the outside edge. Tension along flanges on the inside prevents the possibility of localized bucking in the flanges from compressive forces. Figure 2: Orientation of Sleeve Channels to Prevent Localized Buckling.

Additionally, the threaded sleeve section is to have additional thread surface area, shown in Figure 3. These additional threads safely transmit the stress from the power screw to the

sleeve. Threading the thickness of the web of the channel would not be sufficient for reasonable power screw diameters. This addition is only made on the threaded sleeve section and not on the collared sleeve section. The collar transmits the stress safely to the c-shape. Figure 3: Addition to C-Shape to Provide Adequate Threaded Area. : The that make with ground and the service load are 1 and 5 respectively. Member 1 has additional flanges to provide a stable base for the mechanism while servicing the load. Member 5 has an attached plate atop to provide sufficient area. Most scissor jacks have ridges which lower the area of . This causes stress concentrations which can damage the underside of a car.

The Power Screw: The Power Screw is single threaded with a collar on the side in with Member 3. The collar is assumed to be frictionless and the power screw has been designed to be selflocking. The primary raising method is through the power screw’s hook coupling which is common to most scissor jacks. Incorporated into our proposed design is an option for a secondary raising method. The collar on the power screw doubles as a bolt with a hexagonal head. In a situation where the main hook coupling becomes inoperable, a standard socket wrench can be used on the hexagonal nut to raise the mechanism.

Design Criteria The design checks used in the design of the scissor jack are summarized in Table 1. The criteria are organized by failure mode with the applicable identified. Table 1: Design Checks for Different Failure Modes of

Conclusion and Recommendations Our proposed design is similar to common scissor designs in some aspects, but also advantageous in others. Similar to others, our proposed design can safely raise a load of 2000 lbs to the required heights with relative ease on the . Unique to our design, however, is the manufacturability of our design, which is much simpler. Since only c-shapes are utilized, bulk material can be more efficiently purchased and used. Also, less machining is required since there are no complex sleeves for the power screw. Only simple attachments which can be welded on are proposed. Therefore, when compared to similar scissor jack designs that perform equally as well, our proposed design is recommended for its manufacturability and lower cost.

Appendix A: Drawings Note: All Drawings are in Inches

**See ANSYS printouts in Appendix H: All force analysis can be found there

*See “Appendix C ” for ing calculations (not computer-generated)

Appendix H: ANSYS Force Analysis Note: Power Screw is composed of 9 and 10 in ANSYS repor