Coffee grinder

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Hamilton Beach Coffee Grinder
Hamilton Beach Coffee Grinder


Executive Summary

The purpose of this study is to identify potential areas of improvement for a consumer coffee grinder.

The first step of this study was to conduct a user study in which we evaluated how the average consumer uses the product, taking into consideration how intuitive the product is, and to what degree the product meets the consumer's needs. We observed that the product is generally simple to use without reading the instructions, but after several uses in a short time frame, our perceived quality of the device was quite low. The product was loud and became very hot after many consecutive uses.

The second step in this study was to dissect the product while noting the assembly procedure and making inferences about the materials used in the design. By noting each component's material, manufacturing process, and function, we are able to understand the intentions of the designers, the quality of the device, and it's impact on the environment.

FMEA analysis revealed that many of the susceptible failure modes result from user error and misuse. The failure modes that were identified as most severe did not rank high overall because their probability of occurrence or difficulty of detectability were low enough to offset its severity. A better designed product would design for the most common misuse failure modes.

Primary Stakeholders and Product Needs

The primary stakeholders for this product are consumers, retailers, distributors and shippers, and manufacturers. The needs of these stakeholders are outlined below.

Coffee Consumers:

  • Longevity
  • Quiet operation
  • Aesthetically pleasing
  • Small footprint/Easy to store
  • Easy to clean
  • Dishwasher safe parts
  • Intuitive and fast operation
  • Versatility


  • Space efficient packaging
  • Light
  • Aesthetically pleasing
  • Low unit cost
  • High demand
  • Stackable

Distributors and Shippers:

  • Light
  • Durable packaging
  • Stackable


  • Easy mechanical assembly
  • High volume parts
  • Inexpensive materials
  • Low overhead costs

Product Function and Use

User Study

The coffee grinder is powered by a typical 110V power outlet. To free the power cord, pull down on the black cover on the bottom of the device. Unwrap the power cord, then replace the black cover. Unlock the top plastic cover by rotating it counter-clockwise.

Cord storage system, opened
Cord storage system, opened

Remove the inner cup and notice the marking lines on the side. These pertain to the number of cups of coffee you intend to brew. Fill the cup with whole coffee beans or raw spices to the desired level. Place the cup back in the device and lock the top cover. The device will not function if the cover is not locked in place.

Top cover (left), back of coffee grinder (rear), cup with measurements (right), and brush (front)
Top cover (left), back of coffee grinder (rear), cup with measurements (right), and brush (front)

Select the quantity of coffee you desire (4, 8, 10, or 12 cups) using the switch on the front of the device. Turn the knob to the desired grind. Press the on button. The device will stop automatically, or you can manually stop the device by pressing the button again.

Front controls
Front controls

Mechanical Function

The coarseness and size selection control the motor speed (driving the blade) and the duration of operation. As one would expect, the larger quantities require longer run times. Interestingly, the finer grinds require slower motor speeds. We suspect that because the more coarse grinds run for a shorter time, a higher speed is required to get a good quality grind. We took some preliminary data to characterize the device.

Three samples of different grinds. As you can see, it is difficult to differentiate the grinds by visual inspection.
Three samples of different grinds. As you can see, it is difficult to differentiate the grinds by visual inspection.
Run Time in Seconds:
Quantity Percolator Drip Espresso
12 cups 10 18 30
10 cups 10 16 30
8 cups 9 14 25
4 cups 9 13 20

Motor Speeds in rpm for 12 Cup Setting:
Percolator Percolator/Drip Drip Drip/Espresso Espresso
Speed [rpm] 25,000 23,000 22,600 22,600 22,500

Close up of cup and blade
Close up of cup and blade
Measuring the motor speed
Measuring the motor speed

List of Parts

The following details the list of parts of a hands-free coffee grinder.

Coffee Grinder Exploded View
Coffee Grinder Exploded View

Bill of Materials

Part Number Name Quantity Mass (g) Function Material Manufacturing Process/ Purchased Component Image
Grinding Chamber Sub-Assembly
1 Lid 1 66 Contains coffee Plastic Blow Molded
2 Flat Head Screws 3 <1 Cup to Scatter Shield Steel Catalog Purchase
3 Female Drive Adapter 1 6 Provides Torque to Blade Assy Plastic Injection Molding
4 Rubber Nipples 3 <1 Vibration Isolation & Noise Reduction Rubber Die Cut
5 Plastic Washer 1 <1 Reduces friction of Blade Assy Plastic Catalog Purchase
6 Cup 1 46 Provides References for Coffee Bean Measuring Plastic Injection Molding
7 Scatter Guard 1 15 Contains Coffee Beans behind the Blade Tin Stamped
8 Dust Shield 1 3 Separates the Grinding Chamber and the Drive Assy Plastic Injection Molding
9 Blade-Adapter Shaft 1 2 Transmits Torque from Part 3 to Part 13 Aluminum Machined
10 Blade Gasket 1 <1 Seals Blade Assy Rubber Injection Molding
11 Blade Washer 1 <1 Reduces friction of Blade Assy and Provides Axial Preload Steel Catalog Purchase
Blade Sub-Assembly
12 Blade Hub 1 2 Connects blade to drive shaft Plastic Injection Molding
13 Blade 1 3 Grinds Coffee Stainless Steel Stamped
Cord Housing Sub-Assembly
14 Tamper Proof Screw 1 <1 Connects cord housing assembly to main body Steel Purchased Part
15 Rubber Foot Pad 3 <1 Prevents Device from Slipping Rubber Stamped
16 Cord Reel Container 1 17 Contains Cord While Wound Plastic Blow Formed
17 Screw 3 <1 Mates Part 19 to Part 28 Steel Purchased Part
18 Power Cord Reel Center 1 3 Cord Capstan Plastic Injection Molded
19 Power Cord Reel 1 26 Captures Cord Plastic Injection Molded
20 Internal Motor Gasket 2 3 Seals Motor Components Rubber Injection Molding
21 Screw For Part 22 2 1 Mates Part 22 to Part 28 Steel Purchased Part
22 Power Cord Retention Clip 1 2 Positively Retains The Power Cord Inside The Housing Plastic Injection Molding
23 Tiny Spring 1 <1 Provides Preload to the Safety Mechanism Steel Purchased Part
24 Safety Paper 1 <1 Reduces Abrasion of Safety Switch Plastic Stamped
25 Electrical Switch Cover 1 1 Houses Electric Switch Plastic Injection Molded
26 Electrical Switch Lead 2 1 Provides Current to Electrical Switch Copper Purchased Part
27 Mechanical Switch 1 1 Actuates the Safety Switch Plastic Injection Molded
28 Motor Housing 1 47 Secures motor to device Plastic Injection Molded
AC Motor Sub-Assembly
29 Brushes 2 <1 Provides Current to Commutator Carbon Electronic Component
30 Motor Shaft Cap 1 <1 Transmits Torque from Part 42 to Part ?? Plastic Injection Molded
31 Shaft Insulator 1 <1 Provides Mechanical and Electrical Insulation to the Shaft Fiber Stamped
32 Spring Washer 1 <1 Provides Axial Preload to locate the commutator with respect to the bushings Copper Purchased
33 Small Brown Washers 4 <1 Locates Part 42 Axially Plastic Stamped
34 Large Orange Washers 2 <1 Locates Part 42 Axially Plastic Stamped
35 Small Metal Washers 2 <1 Locates Part 42 Axially Steel Purchased
36 Bearing 2 2 Locates Part 42 Radially Steel Purchased
37 Brush Side Bracket 1 17 Locate Part 36 on Brush Side Steel Stamped and Bent
38 Non-Brush Side Bracket 1 16 Locate Part 36 on Non Brush Side Steel Stamped and Bent
39 Brush Housing 2 1 Constrains Part 29 Plastic Injection Molded
40 Stator Coil 2 13 Provides Magnetic Poles n/a Electronic Component
41 Steel Inductor Plate 30 4 Enhances Magnetic Poles Steel Stamped
42 Rotor 1 77 Provides Motor Torque n/a Electrical Component
43 Circuit Board 1 28 Assembly Electrical Component
56 Male Drive Adapter 1 15 Plastic Injection Molded
Knob Sub-Assembly
44 Power Button 1 2 Allows user to operate grinder Plastic Injection Molded
45 Power Button Finger 1 <1 Translate power button movement to connect circuit Plastic Injection Molded
46 Knob 1 8 Allows user to adjust fineness of grind Plastic Injection Molded
47 Circuit Board Connector 1 <1 Connects fineness knob circuit Copper Stamped
48 Power Button Spring 1 <1 Returns power button after press Steel Purchased
49 Knob Screws 4 <1 Fastens knob sub-assembly Steel Purchased
50 Detent Springs 2 <1 Pushes ball bearings for discrete adjustment of knob Steel Purchase
51 Detent Bearings 2 <1 Allows for discrete adjustment of knob Steel Purchased
52 Detent Housing 1 2 Contains detent components in knob Plastic Injection Molded
53 Brush 1 3 Cleans coffee grinds Plastic Injection Molded
54 Body 1 74 Houses inner components Plastic Injection Molded
55 Power Cord 1 Supplies electrical current from outlet to grinder Assembly Purchased

Design For Manufacturing and Assembly (DFMA)

Design for Manufacturing [DFM]

The blade adapter shaft that appears to be machined
The blade adapter shaft that appears to be machined

For the most part we believe the coffee grinder was well designed for manufacturing. The majority of the components are injection molded plastic with few post machining operations. While there are a lot of components a quarter of them came from the motor which we are fairly positive was a purchased component.

There was only one component we found that may have been machined and thus has room for improvement. Otherwise the components were, purchased, injection, molded, or stamped.

Furthermore, the only post machining that were very evident to us were cosmetics such as painting the body and painting on brand names and button labels.

Moreover, the PCB, and silver power button were both attached using snap fits, eliminating the need for hardware.

Additionally, while most of components where simple there was a detent button that consisted of many components including steel bearing, springs, and plastic guides. While we are not experts in knob designs we hypothesized that we could create the same motion with a single molded part with a plastic leaf spring. Lastly, the plug capstan had heat vents and other cutouts that we were not positive were necessarily. The motor only got hot after repeated long uses and while the bottom is closed there is only a small hole where the cord comes out of, leading us to believe the vents do not accomplish much.

Other than those two areas we felt that this product was very well designed for manufacturing.

Design For Manufacturing Analysis of Coffee Grinder
Minimize Part Count Well Designed: snap fits on button and attachment for pcb
Room for Improvement: Power knob had many pieces to create a detent (bearings, springs,..), but the detent may have been accomplished with a simpler design
Standardize Components Well Designed: The screws all look like they came from the same buyer and have the same diameter
Room for Improvement: Possibly take it one step further - all the screws were different lengths, maybe possible to standardize screw lengths (possibly done to the best of their ability)
Commonize Product Line Well Designed: The same cup and lid, as well as the same corc holder is used across different products in the companies line
Room for Improvement: None that we could identify
Standardize Design Features Well Designed: Most of the screws were the same diameter and most of the washers where different materials but the same diameters. Many of the injection molded parts were made of the same plastic and therefore could be made on the same injection device.
Room for Improvement:
Keep Designs Simple Well Designed: everything on the outside is very simple. Top, Grinder, brush
Room for Improvement: Plug capstan seems to be overly complicated, some of the other components inside are complicated
Multifunctional Parts Well Designed: The overall grinder is advertised to also function as a spice grinder
Room for Improvement: Top part should have a better seal so it could be used to store and keep ground coffee fresh
Ease of Fabrication Well Designed: mainly easy to manufacture injection molded parts
Room for Improvement: Part 9 actually seems to be machined aluminum
Avoid Tight Tolerances Well Designed: Cord Capstan is very low tolerance because it is not visible to the used
Room for Improvement: The part that holds the motor may not need tight tolerances besides the location for mounting
Minimize Secondary & Finishing Operations Well Designed: almost all of the injection molded parts appear to be ready to use post cooling
Room for Improvement: Body was painted and lettering was inked on instead of made into the mold
Take Advantage of Special Process Properties Well Designed:
Room for Improvement: We did not notice significant designing in this section

Design for Assembly [DFA]

The motor fits squarely into the motor housing and connects with two screws.
The motor fits squarely into the motor housing and connects with two screws.

The coffee grinder has an astonishing number of parts, as can be seen in the Bill of Materials, however, there appear to be no redundant or unnecessary parts. The assembly sequence is very straightforward, with four major sub-assemblies: the cup and lid, the motor and motor housing, the circuit board and front controls, and the cord housing. The cup and lid assembly can be removed effortlessly and separately tested as one unit. The circuit board and customer-facing controls are also one unit and can be tested separately, although cannot be accessed without completely disassembling the device. There is only one way to connect the cup to the rest of the housing, which is inconvenient to the user. The cup could be improved such that it could lock to the rest of the housing in multiple configurations. The motor is sandwiched between two assemblies, the upper cup and blade assembly, and the lower power cord housing assembly. Ideally, the entire motor housing would be accessible from one side of the part, such that the assembly process is linear. Instead, the assembler must rotate the piece many ways in order to stack and secure the parts in the appropriate configuration. Also, the configuration is so specific that many interior parts, such as the motor housing, must be inserted a single way into the outer housing. An ideal design would allow for the parts to slide into place in a logical fashion. Most of the parts are either custom injection molded pieces or specific hardware, like washers and screws. Much of the hardware is consistent. For example, all of the screws take the same size Phillip's head screwdriver. A minimal amount of hardware is used to hold and connect sub-assemblies.

In summary, it is apparent that much consideration went into minimizing the number of parts and optimizing the sub-assemblies, however, the assembly process still requires a non-ideal level of meticulousness and maneuvering.

Failure Modes and Effects Analysis (FMEA)

Studying the failure modes of the coffee grinder allows us to understand which components are more susceptible to failure and the expected lifetime of the product as a whole. Upon inspection, we found that the failure modes identified ranged from extremely severe (operating the grinder with the lid off) to customer annoyance (controls no longer work). However, when taken into account with the frequency of occurrence, the most sever of the failure modes do not pose as high a risk as other failure modes. Additionally, we found that the most severe and most probable failure modes had design controls built into the product to prevent the failure from occurring.

The Risk Priority Numbers are derived from the combination of the severity, probability of occurrence and detectability of each failure mode. The top three failure modes identified are:
(1) the grinder blade is damaged as a result of grinding non-intended objects
(2) the electric motor burns out from excessive usage
(3) the lid and/or body is fractured due to unexpected loads such as the operator's body weight or being dropped.

As can be observed, 2 of the 3 leading causes of failure are directly caused by misuse by the operator (3 out of 3 if the electric motor is excessive used by the consumer). Additionally, many of the other failure modes identified are also related to user error as well. An effective design not only anticipates inherent component failure, but also consumer misuse and incompetencies as well.

FMEA Summary: Table summarizes likely failure modes and effects of various components of the coffee grinder.
(S)everity, Probability of (O)ccurrence and (D)ectability of Failure ratings are assigned following the standards established in Tables 14.12, 14.13 and 14.14, respectively in Dieter and Schmidt.
Risk Priority Numbers (RPN) are generated by finding the product of SxOxD
Item and Function Failure Mode Effects of Failure S Causes of Failure O Design Controls D RPN Recommended Actions
Grinder blade Fracture Catastrophic failure of grinder resulting in a useless product 4 Misuse: grinding unintentional objects 6 Product warnings and guidelines 8 192 Yield before breaking
Hardened lid
Manufacturing defects 2 64
Electric Motor Burnt out motor Inoperable grinder 6 Excessive duty cycle 5 None 5 150 Temperature sensor to force mandatory cool down
Lid and body Crack or fracture At best, unsafe operation.
At worst, inoperable grinder.
6 Unexpected loads e.g. leaning, dropping 5 None 5 150 Use more durable materials
Placing in dishwasher 4 120
Power cord Snapping Faulty electrical wiring
Inoperable product
5 Excessive force from pulling 4 Reenforcing bracket 7 140 Better power cord directions
Lid Safety Switch Switch stuck Blade powers on when lid is off 8 Stiction 2 Friction reducing shim 8 128 Create redundant fail-safe mechanisms
Return spring failure 2 Positive mechanical engagement 8 128
User interface switches Wearing of control mechanisms, breakage Uncontrollable Grinding 3 Fatigue wear 5 None 7 105 Use fatigue resistant materials

Design for Environment (DFE)

Studying the Design for Environment Execution of the Coffee Grinder

DFE Summary: Table summarizes the results of an EIO-LCA to determine the economic and environmental impact of a few key components of the production and use phases of the coffee grinder
Production Use
Item 1 Item 2 Item 3 Item 1 Item 2
Item Purchased Motor Molded Plastic Parts Hardware Coffee Beans Electricity
Economic Sector 335315 - Motor & Generator Manufacturing, Low 325211 - Plastics Material and Resin Manufacturing, High 33272 - Turned Product and Screw, Nut, and Bolt Manufacturing, High 31192 - Coffee and Tea Manufacturing, High 22111 - Electric Power Generation, High
Reference Unit Motor kg kg kg kWh
Units consumed per product life 1 .363 .010 260 .722
Cost per unit 1.00 3.90 15.00 24.00 .14
Lifetime Cost 1 1.42 .15 6240 .10
Economy-Wide Metric Tons of CO2e per $1M of sector output 660 2510 707 913 9370
Implied Metric Tons of CO2e per product life .00066 .00356 .00011 5.70 .00094
CO2 tax at $30 per ton of CO2e .0198 .1068 .0033 171 .0282

On a lifecycle scale, the greenhouse gas emissions of the coffee grinder are dominated primarily by the production of coffee beans. When normalized by product life, coffee beans produce more CO2e than any other item we analyzed by a few orders of magnitude. This can be addressed by reducing the waste beans. We can do this by developing a more sophisticated storage system for ground coffee to preserve freshness for longer.

Adding the CO2 tax that was calculated shows a lifetime ownership cost increase of $171.19, dominated almost entirely by the GHG impact of coffee beans. This represents a total ownership cost increase of approximately 3% Considering that 3% is on the same order as the current rate of inflation, we doubt that adding a CO2 tax will reduce sales significantly.

We are confident in the order of magnitude of our findings. In general, our sectors were very representative of the goods we were interested in (>50%) especially the coffee beans, which represents the overwhelming majority of the emissions.

Table compares the contributions of different sectors to the overall GHG emissions across the different components
Sector MTCO2E per Product Lifetime  % of Total MTCO2E
221100 - Power Generation & Supply 9958.69 74.40
325211 - Plastics Material & Resin Manufacturing 532.00 3.97
331110 - Iron & Steel Mills 470.86 3.52

The vast majority of emissions (~75%) come from upstream emissions. 75% of the total emission come from electricity, but electricity's direct contribution to the products GHG production during the use phase are negligible.

Team Members

Phil Aufdencamp - DFE Czar

Justin Barsano - DFMA Czar

Kristen Hauser - User Study, General Organization Czar

Brian Tang - FMEA Czar


Dieter, George E., and Linda C. Schmidt. Engineering Design. 4th Edition. New York, NY: McGraw-Hill, 2009. Print.

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