• Team Members 

• Industry Contact

• Academic Advisor

• Dr. Faryar Etesami

Overview• Introduction / motivation• Scope• Mission statement• PDS review• Beginning design• Initial design and parts• Initial testing• Refining• Prototype / final testing• Conclusion

Introduction / Motivation

• According to the Consumer Product Safety Commission, injuries suffered from the use of hand held portable circular saws is second only to power drills. The reason for this is due to the inherent danger involved with the saw and its availability to a large cross section of the general population.

Scope

This project involves the following.

•Isolating the blade and electronics

•Stopping the blade

•Adaptation to current circular saws

Mission Statement“To design a blade-arresting device for a hand held portable circular saw that will reliably and effectively stop a moving blade upon contact with human tissue. The device must be readily adaptable for mass production by either existing circular saw manufacturers or by the client company, SawStop LLC.”

PDS ReviewStopping Time: < 0.005 Sec Target 0.003 Sec

Compatible With Other Safety Features

Reliability: > 98% Target > 99%

Does Not Change Ergonomics Or Obstruct View

Lightweight: < 2 Lbs Target < 1 Lb

Cost: < $8 Target < $5

Maintenance Free

Durability: (Withstand a Drop From 6 Ft)

Working Life: > 10 Years Target > 40 Years

Beginning Design• Forces

• Methods of Stopping Saw Blade

• Placement on the Saw

Force On Stopping Block I=moment of inertia=angular momentum=3500rpm=angular accelerationk=radius of gyrationm=mass=0.678 lbmd=diam=7.25inT=torqueF=force

<__Known Parameters

Design Time of .002sec

Force

Methods of Stopping BladePrevious Design Ideas

• Motor Braking– DC current injection. Not Fast Enough

• Friction Braking– Similar to car brakes. More bulky and complex, less

reliable than others and more weight.

• Gear Braking– Pawl in gears. Possible gear damage, blade will still

move

• Impact Braking– More to follow

Placement•Must Be Compatible With Current Safety Features

•Must not obstruct view

•Must not create a hazard

Due to the above restrictions the front of the housing was selected as the best placement.

Initial Design and Parts• Spring to actuate block. Most reliable• Block• Housing• Pivot• Wire

Concept Block

Initial Testing

Testing Materials and Shape

RefiningTesting refinement

Redesigned Test Apparatus –

Uses Spring Actuation to Force the Block into the Blade

Test blocks from second test. Polycarbonate blocks are on the left, and aluminum blocks are on the right.

Test Block Results

Block MaterialBlade Radius R (in)

L R+L D L/D

(deg)d Blade Type # of rev

time (ms @ 4600 rpm)

Comments

3 Polycarbonate 3.63 0.50 4.13 0.69 0.73 32 1.3Freud Diablo 24 tooth blade limiting shoulder (DO 724P)

0.917 23.913 Not Satisfactory

4 Polycarbonate 3.63 0.50 4.13 0.69 0.73 32 1.3Freud Diablo 24 tooth blade limiting shoulder (DO 724P)

0.917 23.913 Not Satisfactory

6 Polycarbonate 3.63 0.50 4.13 0.69 0.73 32 1.3Freud Diablo 24 tooth blade limiting shoulder (DO 724P)

0.958 25.000 Not Satisfactory

7 Aluminum 3.63 0.42 4.04 0.69 0.60 29 1.3Freud Diablo 24 tooth blade limiting shoulder (DO 724P)

0.125 3.261

Works well, sheared off one tip and fractured

another

10 Aluminum 3.63 0.50 4.13 0.69 0.73 33.5 1.18Freud Diablo 24 tooth blade limiting shoulder (DO 724P)

0.125 3.261 Worked Well

1 Polycarbonate 3.59 0.53 4.13 0.69 0.77 34 1.3Oldham Combination Industrial Carbide--24 tooth (725-4524)

0.125 3.261 Works well

2 Polycarbonate 3.59 0.53 4.13 0.69 0.77 34 1.3Oldham Combination Industrial Carbide--24 tooth (725-4524)

0.125 3.261 Works well

9 Aluminum 3.59 0.48 4.07 0.69 0.70 30 1.18Oldham Combination Industrial Carbide--24 tooth (725-4524)

0.083 2.174Broken Tooth,

stopped immediately

5 Polycarbonate 3.25 0.53 3.78 0.69 0.77 34 1.3 Oldham Max Life 140 tooth (D650P)

0.293 7.640A little over the time allotted

11 Aluminum 3.25 0.45 3.70 0.69 0.66 33.5 1.18 Oldham Max Life 140 tooth (D650P)

0.186 4.845Worked Well for

this type of blade

Block Material & Blade Type Performance

Depth lim

iting Shoulder1

Com

bination 2

Fine Tooth3

Springs

Spring Force

<---as design number at 30 degT 54lbf in

T G

30 deg

Let = 26 to 30 deg to account for assumptions and simplifications

<---as minimum at 20 degT 36lbf in

T G

G 1.784lbf indeg

G 2I

t2

20deg

I 0.0197332lb in2

t 0.001s

G I 2

t2

solve G 2I

t2

Sub (eqn 1) and (eqn 2) into (eqn 3)

(eqn 3)T I

Also

(eqn 2)T G

For a tortional spring

(eqn 1) t

2 2

solve 2

t2

Spring Design--Helical Tortional Spring

For the small travel we will assume the angular acceleration to be constant

Spring refinement

Restraining

Prototype

Seal / Insulator

Housing

Final Testing Setup

Testing apparatus

Electrical testing setup

Testing Circuit Schematic

Prototype Test Setup

Prototype Parts

Testing Results

Housing fracture

Testing Results

Blade Stopped in one tooth and simply manufactured block fractured

Final Design

Refinement and changes to be made

•Strengthened housing. Depends on manufacturer

•Better manufactured block

•Cover for housing. Will depend on manufacturer.

Main components including spring, insulator, wire attachment, block and housing performed as expected.

ConclusionThe final design is a stopping device

that is reliable, light (less then ½ pound), fast (one tooth of blade),

Compatible with other safety features, inexpensive (approx. 1.70$),

maintenance free and does not change the ergonomics of the saw.