A motorized blade adjustment for a table saw

A Motorized Blade Adjustment
for a Table Saw
by
BRIAN STOLLMAIER
Submitted to the
MECHANICAL ENGINEERING TECHNOLOGY DEPARTMENT
In Partial Fulfillment of the
Requirements for the
Degree of
Bachelor of Science
In
MECHANICAL ENGINEERING TECHNOLOGY
at the
OMI College of Applied Science
University of Cincinnati
May2002
© ...... Brian Stollmaier
The author hereby grants to the Mechanical Engineering Technology Department
permission to reproduce and distribute copies of the thesis document in whole or in part.
Signature of Author
Certified by
Accepted by
~
Mechanical Engineering Technology
~1)7~~~
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Abstract
A table saw is a manual tool that works on the principle of a continuously
spinning circular blade. The table saw performs multiple cuts to various materials,
mainly wood, at angles up to 45 degrees. The height and angle of the blade on a table
saw is adjusted by means of two separate hand cranks. The problem with the hand crank
method of blade adjustment is it requires both time and user torque. A motorized blade
adjustment system has been developed which integrates DC gearmotors into the existing
adjustment system of a portable table saw therefore decreasing the time and user torque
required to adjust the height and angle of the blade.
Needs analysis techniques were utilized to find the customer requirements of less
time and less user torque for the blade adjustment. Overall weight of the saw was also a
customer requirement due to the relationship between weight and portability. Customer
requirements led to the conception of design alternatives of which the gearmotor
alternative was selected. Components were designed, manufactured and integrated into
the existing system along with electronic components such as a motor controller, power
supply, switches, etc. The electronic components allow the user to interface with the
gearmotors therefore controlling the speed and direction of the gearmotors.
Once
fabrication and assembly were complete, testing was performed on the motorized blade
adjustment to make sure it would meet or exceed the customer requirements.
The table saw originally required 12 lb-in of torque and 20 seconds to fully adjust
the height of the blade. The table saw also required 5 lb-in of torque and 15 seconds to
fully adjust the angle of the blade.
The motorized blade adjustment requires
approximately 0 lb-in of torque and 19 seconds to fully adjust the height of the blade.
The motorized blade adjustment requires approximately 0 lb-in of torque and 10.25
seconds to fully adjust the angle of the blade. The weight of the table saw was to be
equal to or less than 100 pounds.
The weight of the table saw with integrated
components is 93 pounds.
Future revisions to the motorized blade adjustment might include lessening the
weight of the table saw by using lighter weight components, and simplifying the
operation by using a different type of motor controller therefore eliminating one user
interface switch.
II
Table of Contents
Abstract
Table of Contents
List of Figures
List of Tables
1.0 Introduction
1.1 Problem Definition
1.2 Backround
1.3 Scope of Report
2.0 Pre-Design Criteria
2.1 House of Quality
2.2 Measurable Objectives
2.3 Design Concepts
2.4 Selection of Preferred Design
3.0 Design Solution
3.1 Calculating Required Torque and Speed
3.2 Gearmotor Selection
3.3 Gearmotor Testing
3.4 Bracket Design
3.5 Control/Electrical System Design
3.6 Gearmotor Integration
3.7 Control/Electrical System Integration
4.0 Testing
5.0 Conclusion
Appendices
A. Existing Patents
B. Survey/Results
C. Design Concepts
D. Management
E. Calculations
F. Drawings
G. References
H. Proof of Design Agreement
III
I
III
IV
V
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4
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7
7
9
10
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11
12
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19
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35
38
45
47
List of Figures
Figure 1. 10” Benchtop Table Saw by DeWalt
Figure 2. 10” Benchtop Table Saw by Delta
Figure 3. Motor Testing Setup
Figure 4. Height Adjustment Components
Figure 5. Angle Adjustment Components
Figure 6. DC to Pulse Width Modulator
Figure 7. Integrated Height Adjustment
Figure 8. Integrated Angle Adjustment
Figure 9. Integrated Electronics
Figure 10. Integrated User Controls
Figure 11. Manual Lever Concept
Figure 12. Linear Actuator Angle Adjustment Concept
Figure 13. Linear Actuator Height Adjustment Concept
Figure 14 Gearmotor Concept
IV
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13
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18
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List of Tables
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
House of Quality
Measurable Objectives
Pugh’s Selection Matrix
Testing Results
Survey Results
Budget
Schedule
5
6
8
19
27
33
34
V
1. Introduction
A table saw works on this principle of a continuously spinning circular
blade. The table saw is a very versatile tool because it allows its operator to
produce a multitude of cuts to many materials, mainly wide sheets of plywood
and narrow pieces of lumber, with only a few adjustments to the blade. Among
home woodshop owners the table saw is the most popular large power tool (1).
1.1 Problem Definition
Table saws are very useful tools in the world of woodworking but with
their usefulness exists a problem. The problem with table saws is the user must
physically rotate a pair of hand cranks to position the blade in both height and
angle. These actions take a certain amount of time and user torque, especially
when multiple angles need to be cut into a piece of material.
The prototype detailed in this report uses a motorized blade adjustment
method that will do most of the work of the user, therefore requiring less time
and less torque by the user than the hand crank method. Special consideration is
given to the weight of the table saw as well since the prototype is a portable table
saw and weight can affect portability.
1.2 Background
Table saws have been a lifesaver for many wood workers who need their
material cut fast and accurately. Due to the wide array of uses, table saws can
come in all shapes and sizes but table saws all serve the same basic purpose;
making long, straight rip cuts (with the wood grain) and repeated crosscuts
(across the wood grain) much more quickly and accurately than ordinary circular
saws (2).
1
In its makeup a table saw is just what it sounds like: a circular saw blade
set inside a broad, flat table. Blades are always removable in order to replace or
to switch with a different blade since different materials and types of cuts require
different types of blades. Both the cabinet and contractor table saws generally
use a belt drive system for driving the blade, which helps to protect the motor in
case the blade jams. Benchtop table saws use a direct drive system where the
blade is directly connected to the motor. This makes for a less complex and more
compact system than the larger, stationary table saws. The blade and motor are
mounted to the saw frame by a trunnion which is a fancy term for a table saw’s
motor mount. A moveable “fence” or rail at one side of the table acts as a guide
for boards or sheets of plywood as they are pushed through the blade as to keep
them parallel to the blade and at a constant distance from the blade. A miter
gauge sits on top of the table as well. The miter gauge runs through a slot in the
table, running parallel to the blade, allowing material to be run through the blade
at a constant angle (4). The height of the blade from tabletop to blade top can be
adjusted by the rotation of a hand crank by the user. In addition, the angle of the
blade can be adjusted by means of a hand crank. As with most products on the
market, table saws come in low-end, mid-range and high-end models.
Three types of table saws exist in today’s market: high-end ($1500+)
cabinet and arbor-style models, mid-range contractor models and low-priced
benchtop models. The cabinet and arbor-style table saws are permanently placed
models because of their large size. Cabinet and arbor-style table saws are made
for 10”–12” blades however the larger the blade is, the more expensive it will be.
A premium 14 inch saw blade can cost as much as twice the price of the same
blade in a 10 inch size. Contractor model table saws are smaller than the cabinet
and arbor styles and generally use a 10 inch blade. Contractor saws could be
transported from place to place but would require some extra hands to do so
since they are still relatively large. Benchtop table saws perform many of the
functions of larger stationary table saws but have a decided advantage in their
2
mobility. High mobility makes benchtop table saws the perfect choice for
framing and deck building. Benchtop table saws are also a good choice for small
shops with limited space due to the use of a 10” blade and weight between 60
and 100 pounds (2,3). Two common benchtop table saws can be found below in
Figures 1 and 2.
Figure 1. 10” Benchtop Table Saw by DeWalt
Figure 2. 10” Benchtop Table Saw by Delta
1.3 Scope of Report
The remainder of this report introduces certain problems existing with
today’s table saws and discusses the details of a solution to these problems. The
report will span from the early stages of design conception to the testing of a
prototype adjustment system integrated into an existing benchtop table saw.
3
2. Pre-Design Criteria
A need for an alternate adjustment system had to be found which began a
series of tasks known as pre-design criteria. A patent search was performed,
which showed what adjusting methods existed for table saws (see patents in
Appendix A). Information regarding how table saw users felt about the current
blade adjustment methods was found through the distribution of a survey (See
survey in Appendix B). Interpreting what was important to the customer in
order to create possible design solutions was possible by feeding the results of
the survey into a house of quality (See survey results in Table 5 in Appendix B).
Once the most important aspects of the saw and adjustment method were known
from the house of quality, measurable objectives were created which were claims
saying what the finished product would do. Three possible design concepts
were then conceived, which tried to fulfill the key characteristics that the
potential table saw users wanted. One design concept would be chosen, through
the use of a selection method, to be taken to the next stage of design.
In addition to the tasks mentioned above, a budget was constructed which
accounts for all of the items required to complete the assembled prototype. The
project was funded personally except for a few parts, which were furnished by
OCAS. (See budget in Table 6 in Appendix D). A schedule was constructed as
well, which would help the project run smoothly and on time throughout the
year. (See schedule in Table 7 in Appendix D)
2.1 House of Quality
The house of quality was used to organize information from surveys,
interviews and personal experience and interpret what was important to the
customer. When surveyed, people were asked to rate the importance of certain
characteristics of the current blade adjustment method.
The highest rated
characteristics were used as the customer requirements in the house of quality.
4
Engineering characteristics were arrived at as a way to satisfy the customer
requirements.
The engineering characteristic that stood above the rest in
importance was to design an adjustment system that required less user torque to
adjust the blade in height and angle.
Two other important engineering
characteristics were to lessen the time required to adjust the blade in height and
angle and also to keep the weight of the saw as low as possible. The house of
quality can be found below in Table 1.
Table 1. House of Quality
5
2.2 Measurable Objectives
Measurable objectives are claims stating what the finished product will
do. The measurable objectives were created from results of both the House of
Quality and the survey. The results were the weight of the saw, the torque
required to position the blade and the time required to position the blade. For
this project, three measurable objectives were developed.
The measurable
objectives are listed below in Table 2.
Table 2. Measurable Objectives
Measurable Objectives
Time required to fully adjust blade
will be less than 20 seconds for height
and less than 15 seconds for angle.
Torque required by user to adjust the
blade will be less than 12 lb-in for the
height and less than 5 lb-in for the angle.
Weight of saw will be 100 pounds
or less with integrated components.
Values for the measurable objectives were not known at the time the
measurable objectives were created but values were given after testing of the
purchased saw was complete. Determining these values will be explained in
Chapter 3. The measurable objectives became the proof of design, which states
what the completed adjustment system will do and how it will be tested. (See
Proof of Design Agreement in Appendix H).
6
2.3 Design Concepts
Three design concepts were created with the intention of satisfying the
customer’s requirements. The first design concept involved lever arms with
locking mechanisms connected to the trunnion. One lever would adjust the
height of the blade and one lever would adjust the angle of the blade. The user
would simply push the lever arms while watching the blade’s position. Once the
desired position was obtained the user would lock the trunnion in its position.
The second concept used electric linear actuators to act as the muscles of the
operation. One actuator would adjust the height of the blade and one actuator
would adjust the angle of the blade.
Actuators would be connected to the
trunnion and an input from the user through a switch or potentiometer would
activate the actuators and therefore move the blade to the desired position. The
third concept was based on the use of gearmotors. One gearmotor would adjust
the height of the blade and one gearmotor would adjust the angle of the blade.
The gearmotors would connect to the existing components of the saw and do the
work that the user once did. The user would control the speed and direction of
the gearmotors through the use of switches and a potentiometer.
The
gearmotors would rotate the crankshafts, via gears, and therefore move the blade
into the desired position. (Design concepts can be seen in Figures 11, 12, 13 and
14 in Appendix C).
All three concepts had their advantages and disadvantages therefore a
selection process had to be performed in order to choose the best design concept.
2.4 Selection of Preferred Design
Only one design alternative could be taken to the stage of design so the
Pugh’s selection method was performed. The criterion used were the same as
the customer requirements used in the house of quality.
The three design
concepts were compared against the current adjustment method and rated as
being either better, the same as, or worse than the current method.
7
The
gearmotor concept and the linear actuator concept ranked equally higher against
the hand crank method than did the manual lever concept, therefore a decision
had to be made as to which concept would be taken to the design stage. The
gearmotor concept was chosen since the system could be overridden by the hand
cranks in case of motor or electronic failure, whereas the linear actuator concept
could not be overridden. The Pugh’s selection matrix can be found below in
Table 3.
Table 3. Pugh’s Selection Matrix
Now the pre-design criterion was complete. The motorized blade adjustment
method had been selected and there was an idea of what characteristics the
motorized blade adjustment should have. The next stage of the project was the
design stage.
8
3. Design Solution
The motorized blade adjustment had to be designed and incorporated into
an existing table saw, which currently uses a hand crank method for adjusting
the saw blade.
One design criterion was to have the gearmotors work in
conjunction with the existing components of the saw, since this was why the
gearmotor method was chosen over the linear actuator concept.
The blade
needed to be adjustable to the same degree of accuracy as with the standard
adjustment method, which is currently accurate to the degree in the adjustment
of the angle of the blade. The design also had to meet the three measurable
objectives: 1. To fully adjust the height of the blade in less than 20 seconds and to
fully adjust the angle of the blade in less than 15 seconds, 2. The user should use
less than 12 lb-in to adjust the height of the blade and less than 5 lb-in to adjust
the angle of the blade, 3. The saw will weigh 100 pounds or less with the
integrated components.
The first step was to purchase a table saw. The Craftsman portable table
saw model 137.228010 was purchased in January due to its adequate size for
incorporating components but not so large as to become too expensive. Inside is
a motor connected to a trunnion that could raise, lower and pivot. The saw uses
a 10-inch blade and can accept a multitude of different 10-inch blades for cutting
various materials and making different types of cuts. The angle of the blade is
adjustable in 1-degree increments through the pivot motion of 90 degrees vertical
to 45 degrees. The height is adjustable to 3 inches at 90 degrees and 2 inches at
45 degrees. After acquiring the saw, testing was performed to find the torque
and speed required to adjust the blade in both its height and angle. This testing
would allow for the selection of gearmotors that would perform the required
blade adjustments.
9
3.1 Calculating Required Torque and Speed
Calculating the torque required to adjust the height and angle of the blade
was performed in a crude yet effective manner. All that was needed was a ruler
and a scale. A digital fish scale, accurate to the ounce, was used to measure the
force required to overcome static friction and rotate the hand cranks. The scale
was connected to the handle of the cranks and force was applied perpendicular
to the cranks until the cranks started to move therefore giving a value of force
required to overcome static friction. This task was performed several times for
both the height and angle cranks. The force required to move the crank was
determined to be 7 pounds for the height and 3 pounds for the angle of the blade.
Once the forces were known, the radii of the cranks were measured and they
were both found to be 1.625 inches. Through calculations the torque required for
the height was 192 oz-in (12 lb-in) and for the angle, 80 oz-in (5 lb-in).
For determining the required speed of the motors the blade was adjusted
for height and angle multiple times and the time to adjust was recorded. Sixty
seconds was divided by the average time in seconds for full blade adjustment
and this value was then multiplied by the number of revolutions needed for full
blade adjustment. The calculated value would be the minimum number of rpm
needed from the gearmotors to fulfill the time requirement of the measurable
objectives. The values were found to be 110 RPM for the angle and 137 RPM for
the height. (For more detail, see calculations in Appendix E). Gearmotors could
now be selected since the required torque and speed were known.
3.2 Gearmotor Selection
Gearmotors were needed in order to position the blade in height and
angle. The major question was whether to use AC or DC power. The benefit of
AC motors would be that they do not require an external power supply since
they are running off of the same power as the saw motor. The problem with AC
motors is they are larger and do not produce as high a value of stall torque as DC
10
motors of equivalent size. The choice then was to purchase DC gearmotors.
Gearmotors were purchased yet the specifications of the gearmotors were not
listed. The torque and speed of the gearmotors had to be found in order to know
whether or not the gearmotors would meet the requirements of the measurable
objectives.
Testing was performed to find the maximum torque, speed and
amperage draw of the gearmotors.
3.3 Gearmotor Testing
The maximum torque and speed produced by the gearmotors was found
through equations relating motor speed, input current, back EMF and output
torque. When motors are rotated they act as generators and produce a voltage
known as Back EMF (Back Electro-Motive Force). Ke, a constant, is equal to
milivolts of back EMF per rpm. Kt, another constant, is equal to oz-in of torque
per Ampere of input. Kt is equal to 1.35 Ke (7). Now that the equations were
known, a device was needed to test the gearmotors and find their specifications.
The back EMF and rpm were needed to be able to make the calculations therefore
a tachometer and a voltmeter were needed. A tachometer was found in the MET
storage room and had the value of 1.9 Volts per 1000 rpm. The shaft of a
gearmotor, without the gear head, was connected to the shaft of a tachometer
with silicon tubing. The other gearmotor was connected to the opposite end of
the existing gearmotor in the same manner. The setup can be seen below in
Figure 3.
Figure 3. Motor Testing Setup
11
An input voltage of 15 Volts was given to the gearmotor in the center. The
back EMF was recorded from the gearmotor on the left and the output voltage
from the tachometer was recorded. Knowing that the tachometer produces 1.9
Volts/1000 rpm the rpm could be calculated. With the recorded back EMF value
and the rpm, the constant Ke was now known which was found to be 4.085
mV/rpm. When multiplied by 1.35, Kt was given to be 5.520 oz-in/Ampere.
To find the torque of the motor with the gearhead, the gear ratio was
needed. Output voltage of the motor without the gearhead was divided by the
output voltage of the motor with the gearhead. This calculation gave a gear ratio
of 30:1. With a maximum amperage pull of 2.286 Amperes for the gearmotors,
the stall torque of the gearmotors was calculated to be 378.5 oz-in. Speed of the
gearmotors was needed as well. The speed at 15 Volts was found using the
output voltage from the tachometer. The speed was calculated to be 120.6 rpm,
therefore at 24 Volts the speed would be 193 rpm.
The maximum torque needed was 192 oz-in and the maximum speed
needed was 136.5 rpm. The gearmotors were found to deliver 378.5 oz-in of
torque and 193 rpm therefore making them perfect candidates for the job. (For
all calculations, see Appendix E).
3.4 Bracket Design
It was now known that the gearmotors would fit the application therefore
brackets were designed to allow the gearmotors to be integrated into the existing
system. The existing components of the table saw are shown on the following
page in Figures 4 and 5.
12
Figure 4. Height Adjustment Components
Figure 5. Angle Adjustment Components
The current height adjustment consists of an input shaft from the hand
crank connected to a lead screw via gears. The lead screw is connected to the
motor/blade assembly, which slides up and down on a set of runners. When the
user rotates the hand crank the lead screw is rotated therefore raising or lowering
the motor and blade. The brackets containing the existing input shaft were
chosen as the mounting spot for a gearmotor bracket.
The current angle adjustment consists of a lead screw, which is connected
to a hand crank and the motor trunnion. When the user rotates the hand crank
the trunnion swivels on its contact points on the underneath of the table. Since
the trunnion houses the motor/blade assembly the blade changes its angle along
with the trunnion from 90 degrees vertical to 45 degrees. The plastic frame of the
saw was chosen as the mounting place for the bracket housing the gearmotor for
adjusting the blade angle.
Design of the brackets was accomplished with the use of Mechanical
Desktop 6.0, a micrometer and an engineer’s scale. The existing components of
the saw were measured and modeled in Mechanical Desktop 6.0 to allow for the
design and proper integration of the gearmotor brackets. The brackets were
designed with .1 inch thick steel plate, the same material and thickness used for
the existing brackets. (For part drawings, see Appendix F).
Now that the brackets for the gearmotors were designed, a system to
allow the user to easily control the gearmotors in both speed and direction had to
be designed.
13
3.5 Control/Electrical System Design
The user of the table saw must have a way to interface with the
gearmotors in order to adjust the blade’s angle and height. The chosen method
for interfacing with the gearmotors was through the use of PWM (pulse width
modulation). A motor controller circuit converts a DC voltage into a series of
pulses therefore making the pulse duration directly proportional to the DC
voltage. The advantage of this system is the speed of the gearmotors can be
controlled with virtually no power loss in the control circuit (8). The motor
controller can be seen below in Figure 6.
Figure 6. DC to Pulse Width Modulator
The user will interface with the adjustment system by means of two
switches and a potentiometer. First, the user will select whether he/she wants to
adjust the angle or the height. This selection is made on a double pole/double
throw (DP/DT) switch. The next selection is to make the blade height or angle
move in a positive or negative direction. Positive direction for the blade height
would be raising the blade, negative would be lowering the blade. Positive
direction for the blade angle would be increasing the blade angle, negative
would be decreasing the blade angle. This selection is made on a DP/DT switch
with a center off position, allowing the user to break the circuit between the
motor and motor controller. The third step in interfacing with the adjustment
14
system is by means of a potentiometer. The potentiometer is a variable resistor,
which connects into the motor controller allowing the user to regulate the rate at
which the blade adjusts.
Power for the gearmotors needed to come from a 24 Volt power supply,
which would have to be powered from a 110 Volt outlet. For safety reasons and
convenience, it was decided that a set of receptacles would be connected to the
saw, which could be turned off via a kill switch. The receptacles would power
both the saw motor and the 24 Volt power supply. (For a complete wiring
diagram, see Appendix F).
3.6 Gearmotor Integration
Design and layout of all the components was now complete and the
integration of these components into the saw had to be performed so that testing
could take place.
Integrating the gearmotors into the saw started with manufacturing the
gearmotor brackets. The material used for the brackets was .1 inch steel plate,
the same material and thickness used for the existing brackets. A plate was cut
into a 3.0 inch x 6.6 inch rectangle for the height adjustment bracket and a 3.0
inch x 6.2 inch rectangle for the angle adjustment bracket. Holes for mounting
the brackets to the existing components and holes for mounting the gearmotors
were drilled on a mill, as was a hole in one of the existing brackets for the height
adjustment bracket. The plates were then bent on the hydraulic bender to 90
degrees. For the height adjustment, a gearmotor was mounted to the bracket and
then the gearmotor/bracket assembly was mounted to the existing bracket of the
saw with two bolts. One bolt was placed through the newly drilled hole and the
other bolt through an existing hole. The assembled height components are on
the following page in Figure 7.
15
Figure 7. Integrated Height Adjustment
To transmit torque from the gearmotor to the existing input shaft, gears
were needed.
Four gears, identical to the existing gears in the saw, were
purchased. Two gears would be used for the height adjustment and two gears
would be used for the angle adjustment.
In order to connect gears to the
gearmotors an adapter was needed since the bore on the gear was .42 inches and
the gearmotor shaft had a diameter of .25 inches. An aluminum bar was drilled
on a lathe for an inside diameter of .25 inches. The outside of the bar was turned
on a lathe until it reached the diameter of .42 inches. The bars, now tubes, were
cut into two .8 inch sections and two holes, .2 inches in diameter, were drilled
through the side of each tube to accommodate set screws. Gears could now be
placed on the gearmotors. One gear was placed on the input shaft of the table
saw and one gear, along with a gear adapter, was placed on the gearmotor. The
setscrews were tightened and torque could now be transmitted from the
gearmotor to the input shaft. Now that the height adjustment bracket had been
mounted, the angle adjustment bracket had to be mounted to the table saw.
Before mounting the angle adjustment bracket, the lead screw for
changing the angle was removed from the table saw and turned down on a lathe
from .50 inches to .42 inches in order to accommodate the gear. The gear was
placed on the lead screw and the lead screw was then mounted back into the
table saw. Next, the gearmotor was mounted to the angle adjustment bracket
and the gearadapter and gear were mounted to the gearmotor.
The
gearmotor/bracket assembly was then placed on the frame of the table saw in its
16
approximate mounting position, the holes for the bolts were marked on the
frame of the table saw and then the holes were drilled through the plastic frame
with a hand drill and a 1/4th inch drill bit. Then bracket was placed back onto the
frame and bolted down. The assembled angle components are below in Figure 8.
(For complete assembly drawings, see Appendix F).
Figure 8. Integrated Angle Adjustment
The gearmotors were now mounted to the table saw but they could not
produce any results without a control system. The next step was to integrate the
control system into the table saw which would enable the user to easily control
the gearmotors in both speed and direction.
3.7 Control/Electrical System Integration
Integration of the electrical components into the table saw would
complete the design stage of the motorized adjustment system and would allow
for testing of the system to begin. Many items were purchased in order to
complete the integration of the electrical components. These items included a 24
Volt, 6.5 Ampere power supply for powering the gearmotors, a Velleman K8004
DC to Pulse Width Modulator for use as a motor controller, two user interface
switches and the potentiometer along with a soldering iron, solder, 16 AWG wire
and a motor controller box and additional accessories such as an AC receptacle,
wire connectors etc.
17
Four holes were drilled in the table saw stand for mounting the power
supply. The power supply was then mounted to the stand using ¼ inch bolts. A
hand drill was used for drilling three holes on the face of the table saw to
accommodate the user interface switches and the potentiometer. The switches
and potentiometer were then mounted in the holes. The receptacle and kill
switch were mounted to an inside wall of the table saw’s frame with bolts. A
plug was connected to a 9 foot wire, which was connected to the switch. The kill
switch was wired to the receptacle, which would allow the user to cut power to
the table saw and control system. The motor controller was assembled through
soldering and was then wired to the user interface switches and the
potentiometer. A plug was connected to the power input of the motor controller
to allow for disconnection of the power supply if need be. The motor controller
was then mounted to an inside wall of the table saw’s frame and enclosed in a
box to protect it from the environment.
The final step was to connect the
gearmotors to the angle/height selection switch. The integrated electronics can
be seen below in Figures 9 and 10.
Figure 9. Integrated Electronics
Figure 10. Integrated User Controls
The design stage of the project gave an exact target to shoot for with the
measurable objectives. Design, fabrication and assembly of the motorized blade
adjustment was completed in the design stage as well. Testing of the motorized
adjustment system could now take place to make sure all of the measurable
objectives assigned earlier were met.
18
4. Testing
Testing was performed on April 26, 2002. The objective of testing was to
see if the table saw would meet the measurable objectives created earlier in the
year. The measurable objectives were as follows:
1. The time required to fully adjust the blade will be less than 20 seconds for the
height and less than 15 seconds for the angle.
2. The torque required by the user to adjust the blade will be less than 12 lb-in
for the height and less than 5 lb-in for the angle.
3. The weight of the saw will be 100 lbs or less with integrated components.
The blade was adjusted in both height and angle to full adjustment and
the time required for these actions was found using a stopwatch. The weight of
the saw was found by using a bathroom scale. The torques required for the
height and angle adjustments were assumed to be zero since a potentiometer was
now used for the adjustment instead of hand cranks. The results of the testing
are below in Table 4.
Table 4. Testing Results
• Adjustment time:
Angle
Height
Required
< 15 sec.
< 20 sec.
Measured
10.25 sec.
19 sec.
< 5 lb-in
< 12 lb-in
≈ 0 lb-in
≈ 0 lb-in
≤ 100 lbs.
93 lbs.
•User torque:
Angle
Height
•Saw weight:
The measured time to adjust the height and angle of the blade was less
than the required time for adjustment. The torque required for adjustment was
assumed to be approximately zero as explained earlier. The weight of the saw
with the integrated adjustment system was 93 pounds, lighter than the required
weight.
The saw passed the critical point of the project criteria by meeting and
exceeding the measurable objectives.
19
5. Conclusion
This project focused on the development of a motorized blade adjustment that
would exceed the hand crank adjustment method in the areas of time and user torque
required for adjustment of the blade. The requirements of table saw users were found
through various needs analysis techniques, which led to the conception of three design
alternatives. One design alternative was selected and taken through the stages of design,
fabrication and testing.
Time for full adjustment of the height of the blade dropped from 20 seconds to 19
seconds. Time for full adjustment of the angle of the blade dropped from 15 seconds to
10.25 seconds. The torque required to adjust the height and angle of the blade was
virtually eliminated since gearmotors replaced the job that the user once had. With the
integrated components the table saw weighed 93 pounds, 7 pounds under the weight limit
of 100 pounds.
Future development on this prototype might include simplifying the user controls
by using a microprocessor with the motor controller. This would eliminate the need for
the user to select whether to increase or decrease the height or angle of the blade.
Another recommendation would be to lessen the weight of the saw by using lighter
weight components such as lighter weight gearmotors and a smaller power supply.
20
Appendix A
Existing Patents
21
US6,244,149 claimed a method where the cutting tool height is adjusted by
way of a crank and a threaded rod, upon which a rod follower is movably
threaded.
The follower is connected to a height-adjusting lever for slidably
moving the gear case and thus the motor, arbor and cutting tool upwardly and
downwardly depending upon the direction in which the crank is rotated. The
cutting tool angular position is adjusted by pivotably moving the support plate
to change the angle of the blade. The angular position of the support plate is
locked in position by a locking bar, which extends through a slot in the front of
the cutting tool base across the support plate and through a similar slot in a
bracket attached to the rear of the cutting tool base. A cam lever mechanism is
positioned outward of the front of the cutting tool base such that when the cam
lever is pivoted to its locked position, the locking bar is pulled forwardly
compressing and frictionally locking the support plate between the bracket and
the front of the cutting tool base.
US5,875,698 claims a method where the elevating mechanism includes a
threaded rod and a nut which engages a pivoting link. The pivoting link also
engages the cutting tool. Rotation of the threaded rod pivots the link, which in
turn raises and lowers the cutting tool. A spring biases the cutting tool towards
its lower position to remove play between the components. The angulating
mechanism includes a lever, two cams and a locking rod. Rotation of the lever
moves the locking rod longitudinally due to the action between the two cams.
The longitudinal movement of the rod compresses the support plate and
frictionally engages the support plate against a worktable bracket to maintain the
position of the support plate with respect to the worktable.
US5,875,698 makes a claim for just the angular adjustment on a table saw.
It claims a saw blade position setting apparatus of a working table such as a table
saw which is mounted on a support frame and to which a blade assembly is
mounted with a handle assembly including a handle and a handle shaft held by
22
the support frame to be rotatable and operatively connected to the blade
assembly. The blade assembly is supported by a support member connected to
the handle shaft. A clutch mechanism is selectively transmitting rotation of the
handle to a blade assembly elevating mechanism and a blade assembly inclining
mechanism. The elevational position and the inclination of the blade assembly
are adjusted in accordance with the rotation of the handle assembly. A rack is
secured to the support frame and the handle assembly is moved along the rack to
a predetermined angle position. A lock lever is disposed in operative association
with the handle assembly and operatively connected to the clutch mechanism.
The lock lever serves to lock the support member to the predetermined angle
position and is provided with a cam mechanism through which operation of the
clutch mechanism is changed (5).
23
Appendix B
Survey/Results
24
Survey for Table Saws
1. Do you ever work on small projects that require the use of cutting material
(i.e. wood, metal, plastic etc.)?
YES
NO
2. Would a small portable table saw be useful in these situations?
YES
NO
3. Have you ever used a benchtop table saw? (Compact, portable table saw
using a 10” blade)?
Yes
No
4. What did or didn’t you like about the benchtop table saw over
conventional table saws?
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
__________________
5. Rate the hand crank method for blade adjustment.
(Unsatisfied = 1, Satisfied = 5)
Reliability
Durability
Ease of Use
Ergonomics
Time to position
Accuracy
1
1
1
1
1
1
2
2
2
2
2
2
3
3
3
3
3
3
25
4
4
4
4
4
4
5
5
5
5
5
5
6. Put a check by the blade adjustment method you would rather have (some
exist, some do not).
Rotating hand crank
Lever for manually positioning (Moment arm)
Electronic positioning
7. How much would the chosen method from above be a factor in your
buying decision for a table saw?
A little
1
2
3
4
5
6
A lot
7
8. Rate the importance of each aspect of a newly designed table saw.
(Unimportant = 1, Important = 5)
1. Cost over existing models
2. Reliability
3. Durability
4. Ease of Use
5. Minimal Weight
6. Safety
7. Good Ergonomics
8. Time to Position Blade
9. Accuracy of Blade Position
10. Cosmetics
11. Torque required to adjust blade
1
1
1
1
1
1
1
1
1
1
1
26
2
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
5
Table 5. Survey Results
Question 5 (Satisfaction with Hand Crank)
1=Unsatisfied 7=satisfied
Reliability
Durability
Ease of Use
Ergonomics
Time to position
Customer Response
1 2 3 4 5
1 4 11 9 5
2 4 12 8 4
3 15 6 4 2
6 10 12 2
4 12 10 4
Accuracy
10 18 2
Avg.
Satisfaction
3.43
3.27
2.57
2.33
2.47
3.73
Question 6 (Preferable Blade Adjustment Method)
Rotating hand crank
Lever for manually positioning (Moment arm)
4
2
Electronic positioning
22
Question 8 (Characteristic Importance)
Unimportant=1 Important=5
Cost over existing models
Reliability
Durability
Ease of use
Minimal weight
Safety
Good ergonomics
Time to position blade
Accuracy of blade position
Cosmetics
Customer Response Avg. Importance
1 2 3 4 5
1 7 6 12 4
3.37
3 19 8
4.17
3 20 7
4.13
5 6 8 8 3
2.93
1 8 10 11
4.03
2 5 6 16 1
3.30
2 9 12 7
3.80
1 18 11
4.33
25 5
4.17
5 17 5 3
2.20
Torque required to adjust blade
6 12 12
27
4.20
Appendix C
Design Concepts
28
The first design concept involved lever arms with locking mechanisms
connected to the trunnion. One lever would adjust the height of the blade and
one lever would adjust the angle of the blade. The user would simply push the
lever arms while watching the blade’s position. Once the desired position was
obtained the user would lock the trunnion in its position.
Figure 11. Manual Lever Concept
29
The second concept used electric linear actuators to act as the muscles of
the operation.
One actuator would adjust the height of the blade and one
actuator would adjust the angle of the blade. Actuators would be connected to
the trunnion and an input from the user through a switch or potentiometer
would activate the actuators and therefore move the blade to the desired
position.
Figure 12. Linear Actuator Angle Adjustment Concept
Figure 13. Linear Actuator Height Adjustment Concept
30
The third concept was based on the use of gearmotors. One gearmotor
would adjust the height of the blade and one gearmotor would adjust the angle
of the blade. The gearmotors would connect to the existing components of the
saw and do the work that the user once did. The user would control the speed
and direction of the gearmotors through the use of switches and a potentiometer.
The gearmotors would rotate the crankshafts, via gears, therefore moving the
blade into the desired position.
Figure 14. Gearmotor Concept
31
Appendix D
Management
32
A budget was made, which accounts for all of the items required to
complete the assembled prototype. Some of the items were furnished by OCAS
yet most items were purchased. The project was funded personally.
Table 6. Budget
Item
Benchtop table saw
Gearmotors
Motor Controller
Power Supply
Electrical Accessories
Gearmotor mounting brackets
Gear Adapters
Gears
Bolts/Fasteners
Method to obtain Quantity Total Price ($)
Purchase
1
296.79
Purchase
2
21.2
Purchase
1
22.95
Purchase
2
37.28
Purchase
1
65.39
School resources
2
N/A
School resources
2
N/A
Purchase
4
13.39
Purchase
?
10
467.00
Total
33
A schedule was constructed as well, which would help the project run
smoothly and on time throughout the year.
Table 7. Schedule
34
Appendix E
Calculations
35
Finding Required Torque
Height Adjustment
Force = 6 lb 15 oz ≈ 7 lb
Radius = 1 .625”
7 lb * 1.625” = 11.38 lb-in ≈ 12.0 lb-in = 192 oz-in
Angle Adjustment
Force = 2 lb 14 oz ≈ 3 lb
Radius = 1 .625”
3 lb * 1.625” = 4.875 lb-in ≈ 5.0 lb-in = 80 oz-in
Finding Required Speed
Average angle adjustment = 15 seconds.
Revolutions for maximum angle adjustment = 27.5
(60 seconds/15 seconds) * 27.5 = 110 rpm
Average height adjustment = 20 seconds.
Revolutions for maximum angle adjustment = 45.5
(60 seconds/20 seconds) * 45.5 = 136.5 rpm
Motor Equations
Kt = 1.35 Ke
Kt = oz-in/Ampere
Ke = mV/rpm
V=IR
Tachometer = 1.9 Volts/1000 rpm
36
Finding Torque of Motors Per Ampere of Input
1.77968 Volts was measured so:
(1.780/1.9) * 1000 = 937 rpm
Ke = 3828 mV/937 rpm = 4.085 mV/rpm
Kt = 4.087 * 1.350 = 5.520 oz-in/Ampere
Maximum Output of Motors
V=IR
Resistance of motors was measured at 10.5 Ω, therefore:
24 Volts = I * 10.5Ω
I = 2.286 amperes
5.520 oz-in/Ampere * 2.286 Amperes = 12.617oz-in
Gear head is 30:1
12.617 * 30 = 378.5 oz-in
At 15 Volts input to the motor, the tachometer’s output voltage from the
gearhead was used to find out speed.
Average tachometer output = .2293 Volts
.2293 Volts / (1.9 Volts/1000 rpm) = 120.6 rpm
(24 Volts/15 Volts) * 120.6 rpm = 193 rpm
37
Appendix F
Drawings
38
39
40
41
42
43
44
Appendix G
References
45
References
1. “Benchtop Bonanza,” Nov. 2, 2001
http://www.popularmechanics.com/home_improvements/tools/2001/1
0/benchtop_bonanza/index6.phtml
2. “Buying guide for table saws,” Nov 20, 2001
http://170.224.4.200/lkn?action=howTo&p=BuyGuide/chstablesaw.html
&topic=howToLibrary
3.
“Table Saws,” Nov 20, 2001
http://www.toolseeker.com/basepages/toolpages/tablesawinfo.htm
4. “Cut projects down to size,” Oct 25, 2001
http://www.consumerreview.com/guides/homeandgarden/powersaws
_guide.asp
5. “US Patent & Trademark Office,” Nov 6, 2001
http://patents.uspto.gov
4. “OSHA search page,” Oct 26, 2001 http://www.oshaslc.gov/html/dbsearch.html
5. “Faulhaber MicroMo Electronics, Inc,” Dec 4, 2001
http://www.micromo.com/03application_notes/appnote2.asp
6. DC to Pulse Width Modulator. Velleman-Kit K8004 Manual.
Belgium
46
Appendix H
Proof of Design Agreement
47
48
49