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Black & Decker Jigsaw JS515Machine Autopsy Report

Erica Chin16 September 2011ENGR 3330Mechanical Design

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1 Product Overview

The Black & Decker jigsaw (Model # JS515), as shown in Figure 1, has several key features that appeal

specifically to homeowners, hobbyists, and amateur craftsmen. From Amazon reviews1, the tool appears

to be ideal to this market segment due to its convenience and low costnot its precision.

Features. The use of plastic covers as a chassis contributes to the

jigsaws lightweight of 4.66 lb and expected low price. As for

convenience, one of the covers contains an on-board blade

storage that is magnetic and holds up to three blades, shown in

Figure 2. As boasted on B&Ds website2, the jigsaw can accept both

U and T shank blades; switching blades (shown in Figure 3) is tool-

less and intuitive, a particular favorite feature of the Amazon

hobbyists.

1http://www.amazon.com/Black-Decker-JS515-Variable-Jigsaw/dp/B001CL4ZHK

http://www.protoolreviews.com/reviews/power-tools/corded/saws-routers/jigsaw-black-decker-JS515

http://www.homedepot.com/buy/tools-hardware-power-tools-saws-jig-saws/black-decker-4-5-amp-jig-saw-178203.html2http://www.blackanddecker.com/power-tools/JS515.aspx

Figure 1. The JS515

holds features

especially attractive

to hobb ists.

Figure 2.on-board blade storage

http://www.amazon.com/Black-Decker-JS515-Variable-Jigsaw/dp/B001CL4ZHKhttp://www.amazon.com/Black-Decker-JS515-Variable-Jigsaw/dp/B001CL4ZHKhttp://www.protoolreviews.com/reviews/power-tools/corded/saws-routers/jigsaw-black-decker-JS515http://www.homedepot.com/buy/tools-hardware-power-tools-saws-jig-saws/black-decker-4-5-amp-jig-saw-178203.htmlhttp://www.homedepot.com/buy/tools-hardware-power-tools-saws-jig-saws/black-decker-4-5-amp-jig-saw-178203.htmlhttp://www.blackanddecker.com/power-tools/JS515.aspxhttp://www.blackanddecker.com/power-tools/JS515.aspxhttp://www.blackanddecker.com/power-tools/JS515.aspxhttp://www.blackanddecker.com/power-tools/JS515.aspxhttp://www.homedepot.com/buy/tools-hardware-power-tools-saws-jig-saws/black-decker-4-5-amp-jig-saw-178203.htmlhttp://www.protoolreviews.com/reviews/power-tools/corded/saws-routers/jigsaw-black-decker-JS515http://www.amazon.com/Black-Decker-JS515-Variable-Jigsaw/dp/B001CL4ZHK

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The jigsaw is able to cut through wood, metal, and plastics with its 4.5 Amp

motor that transmits power to the blade through a scotch yoke mechanism

(Figure 4). As noted by one Amazon reviewer, such a motor is not the most

powerful, and may not fit the needs of professional craftsmen.

Control options available to customers include 45o angle bevel cuts- achieved by

shoeplate adjustment (Figure 5), variable speeds up to 3,000 spm achieved by

the degree to which the trigger is depressed, and a SIGHTLINE Channel that is

supposedly helpful in guiding cuts. No orbital action is achievable with this

jigsaw.

Other features include a fan to maintain cutting visibility and a 6 ft. power cord

for maneuverability.

Compliance. Online specifications and the sticker on the back cover

indicate that the jigsaw is ETL, CSA (Canadian Standards Association),

NOM (Norma Oficial Mexicana), and ANCE (Asociacin Nacional de

Normalizacin y Certificacin del Sector Elctrico) listed; the jigsawfollows the safety regulations of the United States, Canada, and Mexico.

Estimated Retail Price. Given the market segment, for an average household, I would expect that

families would be willing to spend between $35-55 on the jigsaw. I estimated a price range instead of

Figure 3. Tool-free switching of blades. Instructions from manual:

- Hold the saw blade (9) as shown, with teeth facing forward.

- Push the lever (3) downwards.

- Insert the shank of the saw blade into the blade holder (10) as far as itwill go.

- Release the lever

Figure 5. Instruction

manuals directions for

shoeplate adjustment

needed in bevel cuts.

Figure 4. Scotch yoke mechanism

Figure 6. Compliance symbols

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a single price because online stores are usually cheaper, even with shipping costs, than department

stores and sometimes hardware stores. I would expect the jigsaw to be in the $30s because of its

plastic aesthetics. *I estimated the price of the jigsaw before I did any research on it.

Estimated Annual Volume.According to the 2009 census, there are 307,006,550 Americans, 53%

of which are in the working class according to Wikipedia. In my high school the percentage ofstudents taking hands-on classes was roughly around 2.5%. I assumed that 3 out of 10 people

interested in crafts would buy the model based on Amazon reviews. I also assumed that all guesses

were overestimates since people are unlikely to buy multiple units within a short amount of time. I

expected that the overestimates would account for the customers in Canada and Mexico. I then cut

the product of the previous numbers in half arbitrarily to account for physical and bureaucratic

limitations and delays. The final number comes out to roughly 610,000 units.

2 Engineering Review

DOF. There are two rotational degrees of freedomone from the fan, motor, and the hinge in the

on-board blade storage and one DOF from the scotch yoke linkage and shoeplate. There are also

two translational degrees of freedom. The blade and the trigger translate on one axis and the locking

mechanism translates on another.

Structure, Transmission & Power. Most of

the structure is provided by the plastic housing.

Acting like base plates or a framework of sorts,

the internal ribs in each plastic shell helps to

position the majority of the components; the

motor rests in a U-structure created by the ribsin the shell. Screws are positioned by bosses

that are occasionally strengthened by gussets.

The transmission, as mentioned earlier, is the

scotch yoke mechanism that converts the

rotational motion supplied by the power of an

AC motor into the linear motion of a blade.

Design Strengths and Weaknesses.The jigsaws design strengths can be seen in its tool-free

mechanism for switching blades, blade storage, and easy disassemblywhich allows users to easily

replace parts that can easily be ordered online3

. The placement of the vents is a mystery to me. I amnot convinced that the holes would (a) vent well or (b) keep debris out. I am also uncertain about

the necessity for the glob of grease towards the blade end of the housing as indicated in Figure 1.

Additionally, the purpose of the headspace (indicated by the black arrow in Figure 8a) appears

either unnecessary or present for aesthetics sake.

3http://servicenet.dewalt.com/Products/Detail/JS515

Fi ure 7. Transmission and ower

http://servicenet.dewalt.com/Products/Detail/JS515http://servicenet.dewalt.com/Products/Detail/JS515http://servicenet.dewalt.com/Products/Detail/JS515http://servicenet.dewalt.com/Products/Detail/JS515

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Although easily used, the jigsaw also frustrates some users due to the solid opaque shoeplate, which

obstructs the cutting path according to several users online. The locking mechanism, the circular

black button as seen on the cover page, limits the tool to right-handed users. The 6 foot cord is also

an impediment to some, who would prefer to work with batteries since cords can be a safety hazard

at times.

Quality/Failure Modes. The part has no protection against water, so the product can easily fail

due to a short. Incorrect speed settings for the material being cut can break the blade. Dulled blades

or dirtied cutting blades can also become stuck and jam within the material being cut. If the screws

become loose, the plastic cover will fail to serve as support and protection from the elements.

Friction between the gears may also cause the gears to wear.

2 Part

Overview. The back cover of the jigsaw was constructed from polyamide or PA6 with 30% glass

fibres as indicated in Figure 8b. Im guessing that based on the witness lines (Figure 8c), the cover

was made through injection molding. The channels that direct air flow also serve as ribs/support.

Figure 8. (a) Back cover of jigsaw (b) material information

(located where the blue arrow is in a) (c) witness lines

a

b

c

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The choice of material for the casing seems appropriate based on material properties such as high

dimensional stability.

Critical Dimensions. As mentioned earlier, if the screws are not fastened properly, the two covers

will not be aligned properly. Consequently, the placement of at least three bosses is critical; if the

covers are improperly aligned, the ribs may fail to correctly position or rub against internalcomponents. Therefore other essential dimensions include all features tangent to the motor and

blade. Some leeway could be found in the ribs around the switch since a jiggling switch will not

affect the tools performance as much as a jiggling blade.

Unique Features. The panhead machine screws used to secure the plastic

housing have an interesting drive pattern as shown in Figure 9. The choice of

a nonstandard pattern is not apparent, especially since the pattern appears to

be a combination of slotted and torx.

2 Financial Review

Estimated Cost of Goods Sold.If shipping and packaging is $1.00 due to the cardboard box, and the labor and overhead is $2.00 perbox, then the total cost per jigsaw would be roughly $19.

Features vs. Cost.The two year warranty will raise the COGS. However, most of the cost stemming from the warranty

will probably be due to customer service labor costs since the replacement parts did not appear to betoo expensive. Since the number of returns should be relatively low, the cost of the warranty willprobably tack on another dollar to the total cost.

Estimated Company Profit.If the average price per unit is $40 and the total cost is $20, then the profit per unit is roughly $20.On an annual basis, if 610,000 units are sold each year, then Black & Decker should earn around $12million a year.

Solidworks Part.On box.net.

Fi ure 9. Standard screw drive

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Bill of Materials

Part Name Material Qty Est. Cost Sub Total

Structure

General Housing

Front Plastic Casing PA6/GF304 1 $ 0.05 $ 0.05

Back Plastic Casing PA6/GF30 1 $ 0.05 $ 0.05

On-board Blade Storage PA6/GF30 1 $ 0.02 $ 0.02

Bevel

Top Plate Steel 1 $ 1.00 $ 1.00

Bottom Plate Steel 1 $ 1.00 $ 1.00

Fasteners

panhead machine screws, 1.5"5 steel with black oxide 2 $ 0.02 $ 0.04

panhead machine screws, 0.6" steel with black oxide 8 $ 0.02 $ 0.16

panhead machine screws, 0.4" steel with black oxide 2 $ 0.01 $ 0.02

Trigger Mechanism

Buttons ABS 1 $ 0.10 $ 0.10

Casing ABS 1 $ 0.10 $ 0.10

Power

Motor Steel, Plastic, Copper Coil 1 $ 8.00 $ 8.00

Motor Connectors PP 2 $ 0.15 $ 0.30

Transmission

Transmission Shaft Steel 1 $ 1.00 $ 1.00

Linkage Steel 1 $ 0.10 $ 0.10

Saw Blade Locking Lever PA6/GF30 1 $ 0.01 $ 0.01

Blade Clamp Base Steel 1 $ 0.75 $ 0.75

Torsion Springs Steel 2 $ 0.01 $ 0.02

Screws Steel 2 $ 0.01 $ 0.02

Sliders Steel 2 $ 0.05 $ 0.10

Spur Gear Steel 1 $ 1.00 $ 1.00

Large Helical Gear Steel 1 $ 1.50 $ 1.50

Small Ball Bearing Steel 1 $ 0.50 $ 0.50

Large Ball Bearing Steel 1 $ 0.50 $ 0.50

Fan Nylon 1 $ 0.01 $ 0.01

Machined Block 1 Steel 1 $ 0.25 $ 0.25

Machined Block 2 Steel 1 $ 0.25 $ 0.25

Machined Plate Steel 1 $ 0.25 $ 0.25

TOTAL: $ 17.10

4http://www.basf.com/group/corporate/en_GB/news-and-media-relations/news-releases/news-releases-usa/P-10-0060

http://www.merrem-materials.com/uploads/File/Kunststoffen/PA6_GF30_black.pdf5http://www.seekpart.com/company/35664/products/201112114518695.html

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