Project 07 / 10Mechanism design · CAD
Four-Bar Axe Linkage
ME357, Boston University · Fall 2025
A four-bar linkage designed as a swinging axe, with a SolidWorks motion study inside a letter-size page.
- Completed
- Mechanical
- Simulation
Key result
56°
Rocker swing
SimulatedFrom the SolidWorks motion study: the pin joining the coupler and rocker swings about 56° along a 4.24 in radius arc, with the whole motion inside an 8.5 × 11 in page.
Technical highlights
- Four custom links joined at four pivots, with the entire range of motion inside a standard 8.5 × 11 in sheet.
- A SolidWorks motion study traces the coupler–rocker pin along a circular arc of radius 4.24 in.
- Documented with an exploded view, bill of materials and a three-view assembly drawing.
- My contribution
- Design, CAD and the motion study
- Engineering drawings and bill of materials
- Tools
- SolidWorksSolidWorks motion studyEngineering drawings
Overview
A CAD and motion-study project for ME357: a four-bar linkage in which a turning crank swings an axe-shaped rocker down onto a stump. The whole motion stays inside a standard 8.5 × 11 in sheet of paper.
Engineering challenge
The assignment was to design a uniquely shaped four-bar linkage in CAD and run a motion study on it. The entire range of motion had to stay within a standard 8.5 × 11 in sheet of paper.
Design process
I gave the linkage a theme. The rocker is an axe, the base carries a stump and my name, and a crank drives a coupler that swings the axe down onto the stump.
The mechanism has four custom parts (base, crank, coupler and rocker) joined at four pivots. Each pivot is a pan-head screw through a stack of washers and an aluminum spacer, secured with a nylon-insert locknut. The links sit in stepped layers so they can move past each other.
In the SolidWorks motion study I drove the crank around and watched the axe swing. An 11 × 8.5 in boundary is drawn on the view, so I could check that no part leaves the page at any point in the cycle.
I traced the pin where the coupler meets the rocker, exported its X and Y position (126 points over one cycle) and plotted it. The points fall on a circular arc of radius 4.24 in, centered on the rocker's ground pivot, which is the path a point on the rocker must follow. The pin swings about 56° between X = -0.14 in, Y = 2.67 in and X = 3.29 in, Y = 4.74 in, and the path closes back on its starting point after each cycle.
I documented the design with an exploded view and bill of materials, and an assembly drawing with front, side and bottom views.
Analysis & technical details
Linkage kinematics, solved live
The pivot positions and link lengths come straight from the SolidWorks assembly: a 7.000 in ground link, a 2.000 in crank, a 6.000 in coupler and a 4.240 in rocker. Each frame is a closed-form position solution (the intersection of the coupler circle and the rocker circle), not a recorded animation, so dragging the crank reproduces the motion-study path below.
- Crank
- 110.0°
- Coupler
- 18.1°
- Rocker
- 117.9°
- Transmission
- 99.7°
- Pin B x
- 1.52 in
- Pin B y
- 4.25 in
The assembly in 3D
This is the actual SolidWorks assembly, exported as a STEP file and rendered in the browser: the four custom links plus every screw, spacer, washer and locknut. Use the crank slider to move the real parts through the linkage, pull the stacks apart with the exploded-view slider, or pick a part to see what it is.
Rotate, zoom, explode and inspect the real SolidWorks assembly · about 0.7 MB
Testing & results
The motion study shows the whole linkage staying inside the 8.5 × 11 in boundary through its full cycle, with the axe head landing on the stump each time around.
Gallery
