Sand Timer Assembly Line

I worked in a team of five to design and manufacture a two-minute sand timer. The timer was specifically intended to promote proper toothbrushing habits by timing a full two-minute brushing session. It is designed to be mass produced using Boston University's FMC called the Automated Manufacturing Laboratory (ADML).

Product Design & CAD

The first step was to design the timer itself. Traditional sand timers use a curved hourglass shape, but this geometry was not practical to manufacture with the tools available in the ADML. To work within these constraints, I designed a timer in SOLIDWORKS using flat, machinable parts and selected HDPE and acrylic stock materials, both compatible with the lab’s CNC machining capabilities.

HDPE Base

The base contains two triangular sand chambers with slanted slopes at the bottom of the base sit on either side of the body with a small channel connecting them both to allow sand to flow from one chamber to the next.

Cross Section

The slanted slopes were designed on the base of the lid in order to encourage sand flow from the top to bottom chamber. They converge at the center to restrict the flow, we found the exact gap necessary through iterations

Clear Acrylic Lid

The Lid is designed to fit over the extruded rim on the body. Two holes, one on either side of the extruded cut channel, are created for the press fit over the pins on the body.

CNC & CAM Programming

Using the HSMWorks plugin within SolidWorks, I programmed the CNC milling operations for both the lid and base components of the sand timer.

Automated Manufacturing

A major aspect of the project is that it is mass manufacturable using the manufacturing cell called the ADML. The Automated Manufacturing Laboratory (ADML) is equipped with two CNC milling machines, three robotic arms (two for machine tending and one for assembly), and a central conveyor system that connects all stations.

Milling is performed at Stations 3 and 4, while assembly occurs at Station 1. All actions are coordinated with a custom CIM script.

Video Demonstration

Results

Total Cost/Part [1]

11.58$

Throughput

1.7 parts/hour

Total Manufacturing Time

2121s

Assembly Yield [2]

66.66%

Functional Yield [3]

100.00%

[1] Cost assumptions based on operating rates: Robot – $1.00/hr, CNC Mill – $20.00/hr, Conveyor – $1.00/hr. Material rates: High-Density Polyethylene (HDPE) – $0.42/in³, Polycarbonate – $0.53/in³.

[2] Assembly is considered successful if the lid and base press-fit securely without separating after robotic assembly. Passed 4/6

[3] Functionality is met if sand flows freely, gradually, and continuously through the timer. Passed 6/6