Project 08

1         Introduction

Most cars come equipped with screw jacks[1] that cause the distressed motorist or automobile enthusiast (depending on the context on the situation) to rotate a slender rod continuously to raise their car.  Not only is this tiring, but potentially harmful as well, many times I have bloodied my knuckles by scraping them against the pavement while rotating the crank to raise my car from the ground for routine maintenance.  Current scissor jacks are also lacking in safety, the base of most scissor jacks is small and there is no support in the direction parallel to the car body (when operated properly), so the jack is prone to tipping; this is dangerous because the jack is design to lift objects of over 2000 lb.  This project aims to increase the functionality of the scissor jack while maintaining a modest cost by designing and modeling a screw jack with a ratcheting crank that will allow the user to rotate the screw from a more comfortable position with a less awkward motion, and also to enhance safety by increasing the size of the base and adding support on the sides.

1.1       Problem Statement

Design a product by conducting market research, exploring alternative design options, three dimensional solid modeling, and present the final product with rendered images, a design animation, technical drawings, web site and slide show.

1.2       Design Goals

Design a car jack that is easier to operate and safer to use than the current standard without compromising cost or storage, and without adding significant weight.

1.3       Project Management

Figure 1, below, shows an approximate timeline for the completion of various aspects for the project.  The schedule is set so that the project is completed in phases.  Phase I is market research, Phase II consists of the design process, Phase III entails CAD modeling of the design, and the final aspect of the project is the presentation, showcasing the product and the work that went into it.

Figure 1 is a Gantt chart displaying a rough timeline for the task to be completed for the project.

2         Research & Decision Making

2.1       Product Comparison

Below are analyses two other car jacks that are similar to the jack I wish to design.  They represent the two primary models of scissor jacks available; those powered by electricity and those that require manual input.





·         Can lift up to 2,200 lbs.

·         Electric motor powered by a 12V DC power source.

·         Extends 13”, compacts to less than 5”.

·         7’ power cord.

·         Weighs 9 lbs.

·         The electric motor makes operating the jack simple and easy.

·         Can operate jack away from the car.


·    The added weight of the electric motor hurts fuel economy.

·    The motor adds cost ($60-$70) and the increased complexity of the system creates more opportunity for failure.

·    Need of an electrical power source could be a hindrance when repairs are needed on the road.

·         Lifts 2,500 lbs.

·         Extends from 3.75”-15.4”.

·         Mechanical input required.

·         The jack’s simple design minimizes cost ($20), size and weight, so it can be stored easily.

·         Does not rely on electricity.

·         Operating the crank can be difficult.

·         Required to be near (practically underneath a 2,000lb object to operate.

·         Like the product above, there is no stability provided from the sides.

·         Tools to raise the jack are not interchangeable.

Table 1 is a table analyzing scissor jacks available in the market.

From Table 1 it can be seen that the overall concept of the scissor jack is constant and that any new product will be based on that concept.  The products above lack support from the sides, so there is the possibility of the jack tipping (especially on an uneven surface.  During further investigation, I stumbled upon a video showcasing a scissor jack design with side supports.    


Figure 2 is a screen shot from a YouTube video showing a jack design concept.  The video is available at

I would like to incorporate some type of side support in my jack because it enhances safety and redistributes stress, enhancing product life and functionality.

The designs above also lacked interchangeability.  In my design I would like the make it possible for the user to operate the jack with tools other than the crank provided.  

2.2       Preliminary Designs

As stated before, the basic design and mechanics of the scissor jack are simplistic and lend little room for drastic change, so any change will be a modification on this base model.  Below are three preliminary design concepts sketched with Google SketchUp. 




Figure 3 (a) design alternative #1, (b) design alternative #2, and (c) design alternative #3.

Design #1 represents the base model of the scissor jack, it is the most simple.  Design #2 has an extended base to prevent tipping when the jack is under load.  Design #3 also aims to prevent tipping, but also adds stability between the top and bottom of the jack (much like Figure 2).  The stabilizing arms on design #3 raise and lower with the jack, lock into place while rising, and, when the jack is lowered, rotate to compact its shape and make storage easier. 





·         Light weight

·         Simple design (less places for failure)

·         Cheap

·         Uses little material

·         Easy to store

·         Small base makes tipping a risk.

·         No added stability between the top risks a collapse


·         Extended base makes tipping less likely.

·         Simple design


·         No added stability between the top and bottom risks a collapse

·         Shape is not compact, makes storage difficult.

·         Added material, cost weight


·         Adds stability to jack.

·         Extended base makes tipping less likely.

·         Prevents collapse

·         Reduces to a compact shape that is easy to store

·         Stability added with moderate weight increase

·         Added complexity creates more areas for problems

·         Added components add cost


 Table 2 is a chart exploring the advantages and disadvantages of each design.

2.3       Decision Making

To help make a decision for the final design, the table below weighs the attributes of each design.  The designs are ranked on their performance for each category, the best performance receives a 3 and the worst a 1, the values are then totaled to determine the overall best design.  The designs will be assigned values based on their cost, safety, weight and storage (functionality has been omitted from this table because all three designs operate in the same basic manner and are capable of being used with a ratchet).  The values for safety will be rated by 5, 10, 15 because of its importance as a design goal.



Design #1

Design #2

Design #3





















Table 3 is a table weighing the attributes of each design in a table to aid in deciding a final design.

Design #1 uses the least amount of material, so it scored high in cost, weight and storage, but, because of the small amount of material, it is not as safe as the other designs.  Design #2 adds safety but also weight, cost and poor storage.  Design #3 adds safety without compromising on weight and storage, but adds cost because it has the most parts.

2.4       Final Design

Design #3 scored the highest in the analysis of alternative designs because safety is extremely important when designing a product that is to lift a 2,000 lb object from the ground.  I have also decided to lengthen the base of design #3 so that it is the same length as the fully compacted jack.  Design #3 also adds stability with modest increase in weight and no compromise in ease of storage, and its hexagonal screw head lends it to operation by other tools like a power drill or wrench (this product is to come equipped with a ratcheting crank).

3         Sketches

Figure 4 through Figure 6 show the original hand sketches used to begin the 3D modeling phase of the project.  Many of the dimensions and some design aspects of the sketches shown below were changed as necessary by the design during the solid modeling phase.

3.1       Crank

Figure 4 shows the original hand sketches to begin modeling the crank.

3.2       Jack

Figure 5 shows the original hand sketches used to begin modeling the jack.

3.3       Supports

Figure 6 shows the original hand sketches used to begin modeling the supports.

4         3D CAD Models

Pictured below in Figure 7 through Figure 13 are the 3D components and assemblies of the jack and crank modeled with Pro/ENGINEER.

4.1       Parts

Figure 7 through Figure 9 show the 3D models of all the components of the jack and crank.

4.1.1       Jack

Figure 7 showcases the core jack components.  Note that lower arm A & B are identical except that the placement of the gear teeth is reversed on B to permit meshing; likewise for upper arms A & B.  Also note the protrusion on the power screw near the bolt head to fix that end of the screw allowing it to behave as a bolt entering a threaded hole to permit the raising and lowering of the jack.



Figure 7 shows the components of the jack subassembly: (a) & (b) the base, (c) lower arm A, (d) lower arm B, (e) upper arm A,  (f) upper arm B, (g) & (h) the power screw, (i) threaded arm to arm fastener, (j) unthreaded arm to arm fastener, (k) the top, (l) arm to base fastener, (m) arm to top fastener, (n) support to top fastener, (o) support to base fastener.

4.1.2       Supports

Figure 8 showcases the support components.  Note that support base A & B, support casing A & B as well as lock A & B are nearly identical except that they are mirror images of each other because they are located on opposite sides of the jack.  The lock was constructed by merging two components and smoothing over with rounds much like a weld.


Figure 8 shows the components of the support subassembly: (a) & (c) support base A, (b) & (d) support base B, (e) support arm casing A, (f) support arm casing B, (g) lock A, (h) lock B, (i) support arm, (j) support top, (k) support arm to top fastener, (l) casing to base fastener.

4.1.3       Crank

Figure 9 showcases the crank components.  The handle of the crank is connected to the socket with a pin and allows the handle to pivot about the pin axis.  This assembly provides a pseudo-ratcheting motion without the complexity of a ratchet.  The crank was originally designed to be a ratchet; the reason for this design change is addressed in section 7.1.

 (c) (d)

Figure 9 shows the components of the crank subassembly: (a) & (b) socket, (c) handle, (d) pin.

4.2       Assembly

Figure 10 shows the fully assembled and constrained jack.  The pictures show how the jack’s supports rotate from parallel to orthogonal to the base, and vertical motion of the jack.  An animation showcasing the jack’s movements can be found at the URL provided in section 0.






Figure 10 shows the fully assembled supported jack at various positions (a) compacted, (c) lowered with supports out, (c) extended.

Figure 11 shows exploded views of the jack assembly to give a general idea of how the components fit together.  The design animation mentioned above also shows all component positions of the jack.




Figure 11 (a), (b) & (c) show the assembled jack assembly exploded at various positions.

Figure 12 shows the hidden moving components of the jack by making their masking components transparent.  Most of these hidden components are shown in the design animation ((c) and (d) are not shown directly in the animation, but the power screw can be seen rotating.)


Figure 12 shows various hidden moving components of the jack: (a) meshing of the lower arms, (b) meshing of upper arms, (c) & (d) power screw through fasteners, (e) locking mechanism.

Figure 13 shows the crank in constrained and exploded views.



Figure 13 shows the crank assembly: (a) fully constrained, (b) exploded.

5         Technical Drawings

Figure 14 through Figure 22 contain the technical drawings showing the composition of the entire system (jack and crank) broken down into subassemblies with bill of materials (BOM) and dimension components.  Larger copies of all of the drawings below are attached to this report.

5.1       BOM Drawings

Figure 14 through Figure 18 show the components which make up the system’s subassemblies.

Figure 14 shows the supported jack assembly & subassemblies.

Figure 15 shows the support arm A subassembly & BOM.

Figure 16 shows the jack subassembly & BOM.

Figure 17 shows the support arm B subassembly & BOM.


Figure 18 show the crank subassembly & BOM.

5.2       2D Parts

Figure 19 through Figure 22 show the dimensioned components indicated in the subassemblies above.

Figure 19 shows the dimensioned support components.

Figure 20 shows the dimensioned jack components.  The bolt head thickness for the power screw was determined from a mechanical engineering design textbook.[1]

Figure 21 shows the dimensioned jack fasteners.

Figure 22 shows the dimensioned crank components.



6         Presentation

The sections below present the polished and finished product with rendered images highlighting the materials and textures of the components and design animations showing the operation of the jack and crank and the positions of all jack components.

Below is a PowerPoint slide show of a presentation of this product.  Slides 8, 10 & 11 do not function properly because they require macros which are not supported by Google.  The entire presentation with macros enabled is attached to this page.


Below is a video of the presentation of this project.

6.1       Renderings

Figure 23 shows rendered images of the jack and crank at various positions in a pavement environment.  The crank, all fasteners, power screw, support arms and locks are rendered as stainless steel.  All other components are rendered as cast iron.






Figure 23 shows renderings of (a), (b), (c) & (d) the jack at various positions (some with crank) and (e) the crank.

6.2       Video

A video animation showcasing the operation of the supported jack is available below.


Not Rendered:  

7         Discussion

7.1       General

The original design as stated at the beginning of this report and in the preliminary sketches was to have a ratcheting crank to allow for easier movement and less awkward positioning while operating the jack.  During the modeling process it was discovered that the amount of intricate components that would be required to assemble a ratcheting crank was not feasible from a cost or product life stand point.  The jack and crank must be dependable, ready to work at anytime.  The jack and crank are stored in a corrosive environment (as I have found after cleaning out my trunk after the winter).  Should the many moving parts of the ratchet rust, it could cease function leaving the stranded motorist out of luck after a blow out in the middle of nowhere.  The simplified crank design is much cheaper to produce as it has far fewer parts than a ratcheting crank would require and is more reliable because it does not possess small, intricate moving parts.

Figure 24 shows part of the ratchet that would be housed in another casing or handle and then attached to a socket.  (b), (c) & (d) show how the ratchet operates; the axel is turned, the lifter and spring are turned with it, the locking mechanism is pressed down and locks into another set of teeth depending on which was the handle is being turned the locking mechanism will lock or rotate providing the ratcheting function.  The complexity of this process does not lend a ratchet to be stored in a corrosive environment, such as the trunk of a car.





Figure 24 (a) shows the original ratchet design, (b), (c) & (d) show the internal components of the ratchets at various positions (showing Pro/E’s flexible spring cababilities).  The modeling of flexible springs was learned from two online tutorials, one to make the spring flexible[2] and another to fix the number of coils on the spring[3].

7.2       Cost Analysis

The entire system consists of two durable materials with relatively low costs.  The components are not large or too complex, so a large amount of material is not required per jack/crank.  The overall cost of the jack and crank is relatively low.   However, the cost compared to an unsupported jack with bar crank is higher because the number of parts has increased.  The cost increase is offset by the added safety and functionality of the supported jack both of which were the overall goals of this design.

7.3       Product Life Analysis

The product is guaranteed for life in the user manual because of the strong materials it is made from.  The jack is also not an “everyday use” product, so the only wear and tear it sees is from possible corrosion.  All fasteners and the majority of moving components are made from stainless steel the remaining components are comparatively large and would take a while to corrode (longer than the life of the vehicle) should they be exposed to a corrosive environment.

7.4       User Manual

A user manual detailing the safety precautions, operation and warrant associated with the jack is attached to the report.

8         Conclusion

The goals of this project were to design a safer, easier to operate car jack without significantly increasing cost and weight or compromising on storage capabilities.  I am satisfied that this goal has been met completely.  The increase of cost and weight is unavoidable when attempting to enhance safety, but the amount of material added to the base scissor jack design will not increase the cost too drastically and it will certainly cost less than an electrically powered scissor jack that does not possess the same safety features.  The crank with pivoting handle makes operating the jack easier, and the rotating support arms reduce the jack to a compact state for storage.

9         References

[1] Car jacks that raise and automobile by rotating a power screw to move two hinged joints together, increasing the height of the assembly and forcing an object (automobile) underneath upward.

[1] Budynas, R. G., Nisbett, J. K., 2008, Shigley’s Mechanical Engineering Design, Eighth Edition, McGrawHill, Table A-27, pp. 1029.

[2]TUTORIAL: Spring - Make Flexible in Pro/ENGINEER Assembly,” [Online], Available:

[3]TUTORIAL: Relation in Spring Model for ‘Make Flexible’ in Pro/ENGINEER,” [Online], Available:


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