Wt5912 2012 u2-w3

WT5912
TECHNOLOGY EDUCATION &
WORKSHOP PRACTICE 2:
MATERIALS AND CONSTRUCTION
UNIT 2 – WEEK 3 Machine Anatomy
and Construction
Course Involved: Graduate Diploma in Technology Education
Studies Detail
University of Limerick
Department of Design & Manufacturing Technology
Lecturer/Teacher: Mr. Joseph Lyster
Academic Year 2012: Spring Semester
Technical Support: Mr. Joe Murray & Mr. Richie Hennessy
Notes Prepared by: Mr. Joseph Lyster
Available on www.slideshare.net/WT4603

UNIVERSITY of LIMERICK
OLLSCOIL LUIMNIGH

MACHINE ANATOMY

WT5912

Surface Planer Thicknesser Rip/Panel Saw

-Machine Parts
-Machine Design
-Machine Function
-Machine Safety/Use
-Machine Processes
-Machine Maintenance

SURFACE PLANER

 When planing wooden material a number of factors
combine to generate the flat surface.
 Number of cutting knives in the block
 Speed of the revolving block
 Feed speed of the material
 Knife cutter design
 Chip breaking aids
 Nature and species of the material

MACHINE DESIGN: CIRCULAR CUTTER BLOCK

• Reduced noise levels
• Better balance
• Safer clamping mechanism
• Can run head at higher speeds (RPM)
• Can produce better finish
• Easier and quicker maintenance

Department of Manufacturing & Operations Engineering


KNIFE CLAMPING MECHANISM



CUTTER PROJECTION

Use of a limiter to achieve limited cutter projection



CUTTER PROJECTION
 The cutter projection and the shape of the block face cause
the severed chip to bend back causing a crack across its
width
 This makes long grain riving less likely
(Chip breaker not shown)

MACHINE DESIGN: PLANER KNIVES

Planer Knives
Impor tant factor s when selecting a planer knife

 Suitability for cutter block

 Material being processed

 Finish required

 Volume being machined

 Clamping and setting mechanisms

 Planers can have 2,3,4,6……. Cutter knives.

 Most smaller machines such as those found in schools will have 2,3
or 4 knives.


 Knives can be made from Chrome Vanadium steel
alloy.
 This is suitable for machining softwoods and non
abrasive hardwoods.
 However with advances in machining technology
better materials have been developed to machine
wood and wood composites.
 Chrome Vanadium knives dull quickly on harder
more dense material.
 This requires more sharpening, setting up and
leads to a lot of time wastage.


 High Speed Steel (HSS) is a cobalt steel alloy with a small
percentage of Tungsten added.
 It is more suitable for machining all types of wood than the
chrome steel compounds.

 Abrasive stock should be machined using solid or tipped
cutters.
 Tungsten Carbide (TC) is the best tool compound for
machining manufactured boards.
 For general work HSS cutters are preferred to TC
 Cutters can be re-sharpened easily.
 A keener edge can be achieved on HSS giving a better finish


 The reason for this is that steel compounds are smelted and
shaped by rolling and forging while the metal is close to
melting point.

 The molecules of the compound flow and align themselves in
response to this pressure giving the material maximum strength
and edge holding capabilities



 Tungsten carbide is a sintered compound. The fine grain
powder from which the cutter will eventually will be made is
compressed into a mould ( the ‘blank’ un-edged cutter
required) under extremely high temperature (1500 C) and
pressure to form a solid block.

 Tungsten does not flow – it retains a granular structure and
will chip rather than deform if abused.



 Because if its brittle nature TC cutters require a more
obtuse sharpness angle than the HSS cutters (more support
for the cutting edge).

 This makes it less satisfactory for cutting softwoods than
HSS knives which can be ground to a more acute cutting
angle.



Cutter Cutter
Knife Knife

H SS
TC

Large grinding angle Smaller grinding angle
to support cutting edge produces keen edge


MACHINE FUNCTION: KNIFE CUTTER GEOMETRY

 Rake or Cutting angle

 Angle created between the
face of the cutting knife Cutting
and the centre of the cutter Angle
block

 Can have a wide range

 Softwoods 27 to 35
 Hardwoods 15 to 25



Bevel or Lip Angle

 Angle formed to give
the cutting edge
Bevel
 Minimum of usually Angle
35

 Greater for tipped
cutters



Clearance Angle

 Angle formed between
a line tangential to
cutting circle and the
bevel angle of the
Cutter Circle
knife Diameter
 Must be present Clearance
Angle
 Has a bearing on the
life of the cutting edge
 Usually 10 to 15



Peripheral Cutting
Speed
Cutter
Rotation
 A constant speed in
the range of 35-45
m/s will give best
results
 Increase in speed may Cutter Circle
cause loss of dynamic Diameter
balance due to
vibrations
 Poor finish
 Increased noise levels
Work Movement Direction


MACHINE FUNCTION

PITCH DISTANCE
 Combination of a rotary Pitch

cut and a linear feed
will leave the surface of

t
the material with a Work Piece
Fast Feed Rate
series of arcs on it
called Curtate Trochoids Pitch

 The pitch and depth of Work Piece

t
these arcs will Slower Feed Rate

determine how smooth
t = Cutter arc depth on
the surface finish will machined surface
be

MACHINE FUNCTION

P I T C H D I S TA N C E

 2mm to 3mm for non obvious joinery and painted
external work.

 1mm to 1.5 mm for internal painted work.

 0.5mm to 1mm for hardwood joinery and
furniture.


MACHINE FUNCTION

PITCH DISTANCE
The SI unit of time is the second , but the minute is acceptable.

Feed rate on wood working machines is expressed in metres per
minute. (m/min)

The formula for the pitch of the cutter marks is given by:
f
p = -------
nR
where p = pitch of cutter mark

f = fe e d r a te

n = n u m b e r o f e f fe c t i v e c u t te r s

R = r e v o l u t i o n s p e r m i n u te o f b l o c k


MACHINE FUNCTION

PITCH DISTANCE

The unit for “p” will be metres (m)

f m/min m min
p = ---- = --------- = ----- x ------ = m
nR 1/min min 1


MACHINE FUNCTION

PITCH DISTANCE

Problem 1

Calculate the cutter pitch of a 4 cutter block revolving at 4200
rev/min with a feed speed of 24m/min.

F 24 24
p = ------- = ------------ = --------- = 0.0014m = 1.4mm
nR 4 x 4200 16800
(Internal painted work)


MACHINE FUNCTION

PITCH DISTANCE

If a graded surface is specified and the machine has a multi -
speed feed gearbox, the same formula is used but “f” is
expressed in terms of n ,p, and R.

f
p = ------- f = nRp
nR


MACHINE PROCESSES: CHIP FORMATION


MACHINE SAFET Y AND USE

Continuous improvement


RISK MAGNITUDE


RISK ASSESSMENT

MACHINE PROCESSES: CHIP FORMATION

 Chip breaking aid
and pressure bar
prevent riving and
splintering


MACHINE MAINTENANCE

Cutter and Machine Maintenance

Involves:

1. Grinding and setting of knives

2. Roller and pressure bar setting

3. Prevention of resin build up on table and rollers.

4. Attention to:
 bearing wear
 feed complex adjustments
 rise and fall table


MACHINE MAINTENANCE

Grinding
 The grinding angle of a cutter can vary between 30 to 35
 This is increased to 40 for hardwoods (cutting edge lasts
longer)

Overheating
 May produce micro cracks in the cutting edge which can
run into gaps when the cutter is used.
 May cause the cutter to bow due to expansion.


MACHINE MAINTENANCE

Overheating can be avoided
 By taking light cuts.

 By ensuring that the grind wheel is ‘dressed’ when required to
ensure that the face is open and not glazed when grinding the
knives.

 By using a ‘soft’ grinding wheel on HSS cutters – the soft
structure of the wheel allows its grains to break away as soon
as they are blunt revealing sharper ones.

 By wet grinding – this is the grinding of cutters while partially
submerged in a mixture of water and soluble oil. The water is a
coolant to prevent frictional heat developing and to disperse it
should it occur. The oil prevents rust in the cutters and it provides
a degree of cutting lubrication .


MACHINE MAINTENANCE

Setting Cutters in Block

 Before setting the following points should be checked.

 The out feed table and cutter block must be clean and free
from dust resin.

 Method of adjusting cutters.

 Area where setting device is used from should be free from
resin and damage.

 Straightness of cutters.

 Cutters correctly balanced both in weight and end for end.


MACHINE MAINTENANCE

 Setting of knives will greatly depend on the type of
cutter block
 Knife cutter projection
 Chip breaker
 Knife parallel to table
 All knives in the same peripheral cutting circle
(Refer to machine manual for setting)


MACHINE MAINTENANCE

Setting devices
There are a number of cutter setting devices.
This device and procedure will often be supplied with the machine.
They can be loosely placed into the following four categories:

1. Bridge device

2. Precision cutter setter device

3. Pin locater device

4. Wooden straight edge device

5. Cutter s require accurate setting in the block because if the knives
are not revolving in the same cutting circle a poor finish will be
produced.


MACHINE PARTS/USE: THICKNESSER

CIRCULAR SAWING MACHINES

NOTE Circular sawing machines are high risk woodworking
machinery

Pupils should not be permitted to use this machine.
BS 4163:2000

The machine should be included in a planned maintenance
program that should include electrical safety tests.
Read Circular Sawing Machines (Week 6 Notes)

MACHINE DESIGN: SAW BLADE

 Hook Angle
 Edge Clearance
 Pitch
 Gullet
 Plate Tension
 Riving Knife
 Table Slot
 Guards
 Fence


TOOTH CONFIGURATION

 The shape of the saw blade tooth and the way the
teeth are grouped also affect the way the blade
cuts. The configuration of the teeth on a saw blade
has a lot to do with whether the blade will work
best for ripping, crosscutting, or laminates.

 Of course, no matter which tooth design you're
looking at, more teeth will give you a smoother cut
than fewer teeth.

TOOTH CONFIGURATION


TOOTH CONFIGURATION

A cross cut blade will do the
A ripping blade will have a Flat best job with an Alternating
Top Grind (FTG) for fast cutting Top Bevel (ATB), cutting across
with the grain. the grain like a knife and
producing a ver y smooth cut.

A blade with Triple Chip Grind (TCG) is
good for all-purpose cutting and also
gives you a ver y clean cut.
TCG blades are also good for cutting non -
ferrous metals and plastics.


TOOTH CONFIGURATION

 In general, blades with more teeth yield a smoother cut, and
blades with fewer teeth move material faster.

 A 250mm blade designed for ripping wood can have as few
as 24 teeth, and is designed to quickly move material along
the length of the grain.

 A rip blade isn't designed to yield a mirror -smooth cut, but a
good rip blade will move through wood with little ef fort and
leave a clean cut with a minimum of scoring.


TOOTH CONFIGURATION

 A crosscut blade is designed to give a smooth cut
across the grain of the wood, without any
splintering or tearing of the material.
 A crosscut blade will usually have from 60 to 80
teeth. More teeth mean that each tooth has to cut
less material.
 The result is a cleaner cut on edges and a smoother
cut surface. With a top-quality crosscut blade, the
cut surface will appear polished.


HOOK ANGLE
In both Rip and Cross -cutting saws the Hook angle determines

 The feel of the cut
 The quality of the finish
 The power consumed

 The approach angle of the saw varies according to the relative
position of the tooth in the downward cutting arc.

 This angle alter s from the top plane of the timber where the tooth
top makes fir st contact to compress the timber before the tooth
point engages, to a plane where the tooth angle and the timber face
are parallel.


HOOK ANGLE

Hook Angle


HOOK ANGLE
 The amount of Hook determines the degree to which
the tooth will drive into the timber during the cut.
 The effect is of the timber being drawn forward.
 The greater the hook angle the greater this tendency.
Too great of a hook angle will result in
 Harsh cut
 Tearing
 Poor finish
 Less rigid tooth
 Vibration.


HOOK ANGLE
 A blade with high positive hook angle (+20 ) will have a ver y
aggressive cut and a fast feed rate.
 A low or negative hook angle will slow the feed rate and will also
inhibit the blade's tendency to "climb" the material being cut.
 A blade for ripping wood on a table saw will generally have a high
hook angle, where an aggressive, fast cut is usually what you
want.
 Radial arms saws and sliding compound mitre saws, on the other
hand, require a blade with a ver y low or negative hook angle, to
inhibit overly fast feed rate, binding, and the blade's tendency to
tr y to "climb" the material


HOOK ANGLE
 On most saw blades, the tooth faces are tipped either toward
or away from the direction of rotation of the blade, rather than
being perfectly in line with the centre of the blade.
 Hook angle is the angle formed between the tooth face and a
line drawn from the centre of the blade across the tip of the
tooth.
 On a blade with a positive hook angle, the teeth are tipped
toward the direction of the blade's rotation.
 A negative hook angle means that teeth tip away from the
direction of rotation, and a zero degree hook angle means that
the teeth are in line with the centre of the blade.


GULLET
 The gullet is the space cut away from the blade plate in
front of each tooth to allow for chip removal.
 In a ripping operation, the feed rate is faster than in
crosscutting and the chip size is bigger, so the gullet
needs to be deep enough to make room for the large
amount of material it has to handle.
 In a crosscutting blade the chips are smaller and fewer
per tooth, so the gullet is much smaller. The gullets on
some crosscutting blades are purposely sized small to
inhibit a too-fast feed rate, which can be a problem,
especially on radial arm and sliding mitre saws.


GULLET
The gullets of a combination blade are
designed to handle both ripping and
crosscutting. The large gullets between the
groups of teeth help clear out the larger
amounts of material generated in ripping.
The smaller gullets between the grouped teeth
inhibit a too-fast feed rate in crosscutting


CLEARANCE
Work clearance must be provided.

 The saw tooth provides this clearance.
 The „Kerf‟ produced by the teeth must be wider than the
supporting saw plate.
 Steel saws had the kerf formed by bending or „setting‟
alternate teeth laterally.
 With tipped saws the tips are wider than the saw plate and
thus create the clearance.
 Clearance or relief bevels are ground on the sides and the
top of each tooth.


PLATE TENSION

 A flat disc will remain flat and true if turned at a slow
speed.
 When variable stresses are created on this disc due to:
 Braking effect of sawing
 Heating effect of friction
 Outward pull of centrifugal force
 the outer rim area of the disc will expand.

 If the whole area of the disc can expand at the same
rate the disc will remain flat and true.
 This does not happen with a saw blade.
 The central region of the blade is clamped between the
collars and does not expand.


PLATE TENSION
 Only the teeth of the saw blade should make contact with the work
and a por tion of the energy expended in cutting will unavoidably
be conver ted to heat.
 The peripher y of the blade will therefore tend to warm up more
quickly than the main plate body.
 This will cause the peripher y of the blade to expand.
 If this is not taken into account the blade will distor t.
 To prevent this saw blades are „tensioned‟ during the
manufacturing stage.
 Rim speed will determine the amount of tension required in a
par ticular saw blade.
 Thinner saw blades require greater tension.
 Faster saws require more tension.


PLATE TENSION
 Traditionally this was done by highly skilled labour but modern
saw manufacturers use machine operated roller s to achieve a
faster more uniform result.
 This within limits allows the plate to expand uniformly in uneven
temperature gradients.
 A blade which has lost its tension will be seen to be throwing from
side to side.
 This is most noticeable as the blade slows down af ter the machine
is switched of f.
 If this is the case the blade should be removed and sent for
ser vicing.
 This can be reduced by cooling the blade tip while in operation by
packing.


PLATE TENSION

 TC tipped blades have an extremely long life and to assist
the tension factor, slots are incorporated around the edge of
the blade.
 These allow a degree of individual expansion between
segments on the plate edge.
 They also break up harmonic frequencies, which build up
during the sawing process.

MACHINE DESIGN: BLADE GUARD

TOP BLADE GUARD

 Covers the top edge of the saw blade.

 Deflects waste.

 Prevents accidental contact with the uppermost teeth of the
blade.

 It can also limit the ef fects of material rejection.

MACHINE DESIGN: RIP FENCE

Rip Fence Setting

MACHINE DESIGN: RIP FENCE
SETTING
RIP-CUT CROSS-CUT

MACHINE FUNCTION: CALCULATIONS

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