Versatile Automated Component

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Versatile Automated Component
Saw

Tier 1: Morphological Chart

Contents

Introduction

1.


Axis Configuration

2.


Degree of Automation

5.


Beveling System

6.


Arm Track Design

8.


Cutter Head Design

9.


Feed System

11.


Mitering System

13.


Bevel Adjustment Design

15.



Applicable Tier 1 Modules


VAC Saw

17.


Applicable Tier 2 Modules


General

18.

Introduction

The V.A.C. saw requirements can be met number of different ways, all with varying suitability. This module investigates the
various options considered and why they were chosen or rejected. For convenience and consistency, the selected solution is al
way
s
offered last.


The criterion that caused many designs to be rejected was the environment. Cedar dust is corrosive to steel and many other me
tal
s.
When the wood is used in construction it is usually nailed with aluminum, stainless steel, or surface treated nails to preven
t
corrosion. The saw dust in any wood working environment is also destructive to lubricated surfaces. The dry dust absorbs the
moisture and becomes a grimy paste where a clean film of lubricant is expected. Since the part is open to the lubrication, it

is

also
open to the paste allowing the cedar dust to get into the part and begin to erode it.


Another criterion that had a large impact was cost. One major goal of the VAC saw is to create a cost effective solution to h
igh

productivity requirements. As the cost increases, the saw moves away from this goal. For this reason, part that required prec
isi
on
machining were minimized as cost comparisons were made.

Axis Configuration

-
Planer (Modified Table Saw)


A planer arrangement requires five independent axes. The two planer velocities (shown left) combine to make the blade move
through the cut. One of these axes is along the spindle, and the other is perpendicular to it in the plane. The third linear
axi
s is the
elevation control (shown right) and is unlikely to ever need adjusting except change the approach of the blade. The two rotar
y a
xes
(shown centre) control the miter and bevel of the cut.













The planer arrangement can be immediately discarded. Since the work piece is to be held still, the table saw is clearly at a
disadvantage and the proposed modifications cause unnecessary complications due to redundant axes. Coordinating the translati
on
direction and the mitering angle is a complex task and as such does not lend itself easily to machining applications. The sam
e i
s
true of the beveling angle if the work piece is approached from the top. The slightest misalignment in either case would caus
e
eccentric forces which would cause further misalignment and even greater eccentric forces. In short, this system is over desi
gne
d
and overly complex.

Axis Configuration

-
Chop Saw Style


A chop saw arrangement would require one linear and three rotary axes. The rotation axis shown centre is the cutting action,
and

the other rotary axes control mitering (shown left) and beveling (shown right). Elevation is controlled by the linear axis (s
how
n
centre). The cutting action axis is transformed by the mitering and beveling angles, but is always parallel to the spindle.












The chop saw style can also be discarded, there are several minor weaknesses with the design as there are with almost all des
ign
s,
but the major flaw is that it is not designed to cut wide pieces. Because of this, when a wide piece is cut the finish is poo
r o
n both
sides of the piece. Using a very large blade would solve this problem, but this is neither practical nor economical.


The approach to the wood is what causes the finish problem. The teeth exiting the wood are up cutting, while the teeth enteri
ng
are
down cutting. As the blade finishes the cut, the teeth begin to leave the wood at increasing sharp angles. The down cutting t
eet
h are
now leaving a poor finish on the bottom face as they break through and similarly the up cutting teeth are leaving a poor fini
sh
on
the top face. This results in having both faces with a poor finish and a piece that is not presentable.


Axis Configuration

-
Radial Arm Saw Style


A radial arm saw arrangement would require two linear and two rotary axes. The two rotary axes would control mitering (shown
left) and beveling (shown centre), and the linear axes would control the cutting action (shown left) and elevation control (s
how
n
right).











The radial arm saw does not have any major design constraints that make it unsuitable for this application. There are no redu
nda
nt
axes, and the teeth exit the cut only on one face and at a shallow angle leaving at least one face with a good finish and the

ot
her
with a reduced chance of tear
-
out.


There are limitations that this design poses though. The width of material that can be cut by the saw is limited by the trave
l o
f the
blade. A radial arm saw can be expected to have as much as 40 inches of travel and this saw only requires around 37 inches so

th
e
limitations are not interfering with the design requirements yet. If the saw is used for wider pieces, simply changing the bl
ade

will
not be sufficient as with a chop saw, the arm would need to be designed in advance to be longer and accommodate the new width
.
This extension is outside the scope of the project, but may still be accounted for later in the design. This configuration wa
s s
elected
for it suitability to the problem and requirements.

Degree of Automation

-
Highly Automated (CNC)


With a highly automated system the bevel, miter and traverse are all automatically actuated. A cutting list can be entered in
to
the
controller and the machine needs only to be supplied with stock lumber and let run.


CNC machining is usually used with high production machines or more difficult operations such as drilling hole sets or profil
ing

faces. The strength of CNC machines is that they are automatically adjusted giving minimum down time between operations. The
additional hardware and software requirements make the design much more expensive and complex. For simpler operations, such
as this one, the speed advantage decreases and the machine is no longer economical. This control method was reject as being o
ver

designed and uneconomical.



-
Moderately Automated (PLC)


With a moderately automated machine the mitering and beveling are adjusted manually. The feed is automatic, since this is the

simplest operation, and can be done by a PLC controller. The mitering and beveling can be adjusted through electronic devices

such as motors, but controlled by an operator as opposed to the machine itself.


PLC machines do not require the complexity or CNC machines or the additional cost of more actuators and sensors. These more
economical machines are not as capable of carrying out different tasks effectively, but are designed to repeat the same opera
tio
n as
efficiently as possible. In this situation, the mitering and beveling angles will stay constant for long enough periods of op
era
tion to
gain a production increase from PLC technology. This control method was selected for being both economical and productive.

Beveling System

-
Indexed Cutter Head


The plate (shown left) supports the wheels and indexing pin. The plates mount in the rail through the wheels (shown centre),
and

the bracket for the motor and blade mounts to the plates (shown right). The pin moves through the top of the plate and into t
he
top
rail to lock the plate at a certain position and angle. As the plates run along the rails, the three wheels cause the whole m
oto
r and
blade assembly to rotate about the bottom of the blade. The pin rests on support block when the angle is being adjusted and d
rop
s
into the holes when the blade is at the desired angle.










In order to use this design, the motor and bracket need to be strategically shaped and positioned so as not to interfere with

th
e cut
when beveling at a larger angle. If the motor moves with the blade, a bevel gear system is required to keep the motor out of
the

way. This can be immediately rejected since the cost for an efficient gear system at the cutting speeds is too great. Since t
his

option
was rejected the motor must be stationary requiring a flexible coupling to allow the blade to bevel. This can also be rejecte
d o
n the
basis of part availability. A coupling able to flex 45 degrees in either direction is not readily available and should it bec
ome

available it will too expensive for this design. In addition to these problems, the indexing system needs to be very stiff in

or
der to
hold the blade and motor still. The large moments created from the motor weight and cutting forces make this system too heavy

to

operate efficiently. This system was rejected as being impractical even if the additional cost is not considered.

Beveling System

-
Indexed Arm


The beveling arm is pivoted at both ends, and the entire arm bevels about the bottom of the blade. Very similar in design to
the

indexed cutter head, the entire arm is now indexed and the cutter head does not need to bevel. The end plate and end support
(shown right) contain the indexing pin and the hole pattern respectively. The indexing pin is spring mounted to close and ope
ned

by a pneumatic piston. The arm rotates about the lowest point of the blade so this is where the plate and support meet to for
m a

pivot.











The motor could still affect the ability of the blade to cut while beveling, but there is much more space in which to build a

si
mpler
cutter head since it doesn’t need to bevel locally. The main concern is that the moment about the beveling axis will be high
sin
ce
the majority of the weight will need to be at least one blade radius away, and at most probably two blade diameters. The blad
e
sizes usually used for these saws range from 10 inches to 18 inches and so two diameters becomes substantial. This problem ca
n b
e
resolved by adding a counter weight to the end plate at a large radius. The beveling axis is going the be where the blade mee
ts
the
table, which is at least 30 inches high, so the counter weight arm can be as long as 30 inches. This would greatly reduce the

shearing stress in the pin. This design was chosen for simplicity and cost.

Arm Track Design

-
Linear Slider


The slider contains reciprocating ball bearings or roller bearings depending on the model used, usually four sets are used to

pr
event
the various moments. The main problem with these designs is that the are weak when resisting yaw and roll. With a poorly grou
nd
blade, the yawing moment can be substantial and the tolerance for twisting the blade in the cut is very low. This system was
rejected due to low moment resistance.







-
Double Row Slider


In the simplest form, this would be two bars with three linear sliders. Spreading the contact points to resist loads would in
cre
ase the
resistance to moments. The problem with this system is that it requires lubrication, which is not plausible in the dusty envi
ron
ment
in which it will operate. Metal bellows would require that the arm be further extended in order to maintain the travel distan
ce
and
rubber bellows would be defeated by the dry air and corrosive cedar dust. This system was reject due to being unsuitable for
the

environment.


Arm Track Design

-
Track and Carriage


The carriage contains three wheels; the two outside wheels of the carriage run against one side of the rail and the centre wh
eel

runs
against the other side. This system is better suited to its environment than the last two since the track and wheels are avai
lab
le in
stainless steel and the only lubrication is sealed inside the bearings where it cannot become contaminated by the dust. The m
ajo
r
flaw with this system is that it cannot resist roll moments that would come from a poorly ground saw blade. The shape of the
tra
ck
also allows dust to collect and may cause it to seize. This system was rejected primarily since it can’t resist moments.







-
Wheel and Track


This system is better suited to its environment than the lubricated options. The track and wheels are available in stainless
ste
el,
which removes the threat of corrosion from the cedar dust. Lubrication between the track and the wheel improves the performan
ce
of the system, but is not required for normal operation. The lubrication that is required is all sealed in the bearings and p
rot
ected
from contamination. The flaw with this design is that it is more expensive than the other systems since at least three wheels

an
d
two tracks are required. However, it was selected based on its suitability to the working environment and ability to resist m
ome
nts.

Cutter Head Design

-
Hanging Motor


The hanging motor design is an attempt to minimize the moment about the beveling axis. Most of the weight of the cuter head a
nd
the arm (excluding the end plates) is in the motor. This makes the arm easier to bevel when the motor is closer to the axis.
The

motor and the blade have been separated due to beveling complications and connected by a timing belt. Chains cannot be used h
ere

since they require lubrication and are not suitable to the working environment. A flange bearing holds the spindle horizontal

an
d
another bearing is needed to support the motor shaft. The feed mechanism can be attached to the top of the frame. A standard
bla
de
shield can be attached to the spindle or the frame and a vacuum hose can run supports beneath the frame parallel to the blade
.












The moment about the beveling arm is reduced at the expense of increasing the moment about the rail when beveling. It was
decided that the priorities for the cutter head were opposite to this since the moment about the rail limits the parts than c
an
be used
and therefore the cost of the track. The off
-
centre position of the motor is inescapable due to it’s dimensions. As noted earlie
r, a
gearbox cannot be used to change the orientation of the motor due to the rotary speed required. The moment about the beveling

axis is relatively high, and reducing the lever arm for the motor by a small amount doesn’t benefit the design greatly. This
des
ign
was rejected for offering minimal advantages and compounding existing problems.

Cutter Head Design

-
Split Arm


The split arm design is an attempt to minimize the moment about the arm by mounting the motor and the blade on opposite sides
.
The belt is now required to pass through the arm. The top pulley is held in place by the motor and a pillow block and the bot
tom

pulley is held by the spindle and a flange bearing. The pillow block may not be required but has been included in the concept
ual

design and can be easily removed at a later time. The belt then passes through a slot in the bracket and between the two halv
es
of
the arm. The bottom pulley is attached to the spindle with the nut and washer between the blade and the pulley. The spindle
diameter decreases where the pulley joins it allowing the nut to be removed without needing to thread the spindle where it jo
ins

the
pulley. A standard blade shield can be attached to the spindle or the frame and a vacuum hose can run under the motor.










The parts surrounding the blade are packed into a small space, but the blade also has sufficient clearance from the belt that

it

will
not cut or hinder it. The same is true of the mounting plate and although this clearance is smaller the assembly is stiffer h
ere
.
Cutting forces that will cause a moment adding to that of the motor are also reduced from the previous design since the tip o
f t
he
blade is closer to the rails. The weight of the blade creates a moment to counteract the moment from the weight of the motor.

Si
nce
the arm is already split into two parts, the top of the blade can be positioned inside the arm. This reduces the moment about

th
e
beveling axis and allows the belt to be shorter. This design was chosen for minimizing the cost of required components withou
t
causing any potential problems.

Feed System

-

Ball / Lead Screw


The nut or lead is attached to the cutter head and the screw runs along the length of the arm. Since this is the automated pa
rt
of the
machine, the screw is powered by a servo motor.














The problem with this design is that it is over designed. These screws are capable of moving huge loads with high precision,
but

neither are required in this case since the cutting forces from softwood are low and the controller is primarily concerned wi
th
constant velocity, not with position. The precise machining required for the screws and leads make them too expensive since t
he
benefits are not required. The screw needs to resist corrosion from the cedar dust and stainless steel or plastic add to the
cos
t and
friction of the screw. This system was rejected as over designed and uneconomical.

Feed System

-

Belt and Plate system


The belt and plate system is also driven by a servo motor and attached to the cutter head by a clamping plate specially machi
ned

to
fit into the tread. Belts were chosen for the same reasons as in the cutter head.












Belts do have the weakness of being susceptible to wear, but can be easily and cheaply replaced. The flex of the belt allows

fo
r
slight misalignment, which would not be acceptable when using a screw. The precision of this system depends mostly on the ser
vo
used as it would with the lead screw so no accuracy is lost. The back lash when changing directions will not matter since the

controller is only concerned with the speed and a PLC based system does not usually track position. This system was selected
for

its suitability to the environment, low cost, and ability to perform the required task. The timing belt and the vacuum hose c
an
be
adjusted so that they can both be placed below the motor.


Mitering System

-

Far End Track


This system does not require much stiffness in the arm and allows the arm to be lighter and cheaper. The far end (away from t
he
mitering axis) must be on a moving support (shown left). The support runs on a curved track and indexes at five degree increm
ent
s.
The pin is removed and replaced manually and the arm is also rotated by hand.
















The strength of the design is that it doesn’t require gears or motors to make it easy to operate. However, it is also quite e
xpe
nsive.
expensive. Like the arm track, it must be resistant to corrosion and not dependant on lubrication for smooth operation. This
des
ign
was reject for being uneconomical.


Mitering System

-

Gear Section and Servo


This design uses a stepper motor and gear system to rotate the main shaft, but is controlled by an operator through a simple
interface (shown left). The interface is positioned at the far end of the arm where an operator would usually stand and the m
oto
r is
mounted under the cutting table close to the dial. The motor affects the rotation through a gear system also mounted under th
e
cutting table and attached to the main support. The position is held by the motor .













Since the mitering angle is only adjusted when the saw is not cutting, the blade will be close to the axis when rotating redu
cin
g the
load on the motor. The gear ratio and gyroscopic effects reduce the load on the motor during cutting and enable it to hold th
e a
rm
in position against cutting forces and coriolis effects. Plastic gears remove the need for lubrication at an increased cost a
nd
also
reduce the weight of the gear section. Though the stepper motors are expensive, they are less expensive than the track propos
ed
in
the previous design and a coarse step motor will be sufficient for this application. This system was selected for offering a
mor
e
precise, elegant, and slightly cheaper solution.

Bevel Adjustment Design

Lead Screw


The nut is mounted on the end plate, which attaches to the arm, and the supports for the screw are mounted to the end support
. A
s
the screw is rotated, the nut moves horizontally causing the plate to rotate relative to the support. The screw is manually o
per
ated
by a handle at the right side. The nut also moves vertically on the plate along a track system similar to the arm track and i
s
connected to the carriage by a pin joint allowing the nut to remain aligned with the screw while the slider runs on the track
.











The main benefits of this design are that it is easy to use and the load that the screw can exert on the nut removes the need

fo
r a
counter weight cutting the cost of the overall system. While replacing the indexing pin, the screw doesn’t need to be held in

pl
ace
as the correct pitch will prevent any back
-
driving that the weight of the rotating assembly may induce. The screw doesn’t need
lubrication, since the majority of the sawdust is thrown in the opposite direction by the blade and the rotary motion will ca
use

most
of the dust to fall off the screw. A major cause for concern is that the pin joint connecting the nut to the carriage may not

be

ably to
support the large forces exerted by the screw. The main flaw with the design is the cost. The screw alone is an expensive opt
ion
,
but combined with a track system it is too costly. This system was rejected for being overly complex and expensive.

Bevel Adjustment Design

Worm Gear


The connection between the end plate and the support is extended from the initial concept and a worm gear is mounted on the
outside of the support (closest to where the operator of a conventional saw would stand). The worm is driven manually and is
oriented for right handed operators. The casing on the gear assembly has been ignored in the diagrams.













This system has no contact with the end plate and no translating parts. The gear will need the counter
-
weight suggested in the
original presentation of the beveling arm in order to reduce the moments and loads that the worm will be exposed to. The redu
ced

moment and the high gear ratios common to worm gears will prevent any back
-
driving. The gear system may require lubrication,
but can be completely enclosed to prevent contamination of the lubricant. Plastic gears offer a lubricant free option as well
. T
he
system is much less expensive than the lead screw design and is equally effective and easy to use. The is design was selected

as

the
cheapest effective solution.

Applicable Tier 1 Modules

The following modules affected the decisions outline in this module. The explicit and implicit requirements are identified in

th
ese
two modules.


VAC Saw


Requirements

Not Yet Implemented. A description of the requirements for the VAC Saw design


VAC Saw


Functional Structure

A functional break
-
down of the VAC Saw’s tasks


VAC Saw


Component Selection

Not Finished. A guide to the parts selected and the criteria and formulae used to select them.

Applicable Tier 2 Modules

Wood Saws and Sawing Practice


Further overview of existing saw types and blade design as well as how finish and energy consumption are effected by cutting
approach.