wt5912 2012 u2-w3

C o u r s e I n v o l v e d : G r a d u a t e D i p l o m a i n Te c h n o l o g y E d u c a t i o nU n i v e r s i t y o f L i m e r i c kD e p a r t m e n t o f D e s i g n & M a n u f a c t u r i n g Te c h n o l o g yL e c t u r e r / Te a c h e r : M r. J o s e p h Ly s t e r A c a d e m i c Ye a r 2 0 1 2 : S p r i n g S e m e s t e rTe c h n i c a l S u p p o r t : M r. J o e M u r r a y & M r. R i c h i e H e n n e s s yN o t e s P r e p a r e d b y: M r. J o s e p h Ly s t e rAv a i l a b l e o n w w w. s l i d e s h a r e . n e t / W T 4 6 0 3

WT5912TECHNOLOGY EDUCATION & WORKSHOP PRACTICE 2: MATERIALS AND CONSTRUCTIONUNIT 2 – WEEK 3

UNIVERSITY of LIMERICKOLLSCOIL LUIMNIGH

Machine Anatomy and Construction Studies Detail

http://www.slideshare.net/WT4603

MACHINE ANATOMY

WT5912

ThicknesserSurface Planer

Rip/Panel Saw

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

When planing wooden material a number of factors combine to generate the flat surface.

Number of cutting knives in the blockSpeed of the revolving blockFeed speed of the materialKnife cutter designChip breaking aidsNature and species of the material

SURFACE PLANER

MACHINE PARTS

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 Important factors when selecting a planer knife Suitabil ity 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

fi nish

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 (1500C) 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.



CutterKnife

TC

KnifeCutter

HSS

Large grinding angle

to support cutting edge

Smaller grinding angle

produces keen edge



MACHINE FUNCTION: KNIFE CUTTER GEOMETRY

Rake or Cutting angle

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

Can have a wide range

Softwoods 27° to 35 °Hardwoods 15° to 25

°

CuttingAngle


Bevel or Lip Angle

Angle formed to give the cutting edge

Minimum of usually 35°

Greater for tipped cutters

BevelAngle



Clearance Angle

Angle formed between a line tangential to cutting circle and the bevel angle of the knife

Must be presentHas a bearing on the

life of the cutting edge

Usually 10° to 15°

ClearanceAngle

Cutter CircleDiameter



Peripheral Cutting Speed

A constant speed in the range of 35-45 m/s will give best results

Increase in speed may cause loss of dynamic balance due to vibrations

Poor finishIncreased noise

levels

Cutter Circ leDiameter

CutterRotation

Work Movement Direction



Combination of a rotary cut and a linear feed will leave the surface of the material with a series of arcs on it called Curtate Trochoids

The pitch and depth of these arcs will determine how smooth the surface finish will be

PITCH DISTANCE

Work PieceSlower Feed Rate

Work Piece

Pitch

Pitch

tt

t = Cutter arc depth on machined surface

Fast Feed Rate


MACHINE FUNCTION

PITCH DISTANCE

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:

fp = -------

nR where p = p i tch of cutter mark

f = feed rate

n = number of eff ect ive cutters

R = revo lut ions per minute of b lockDepartment of Manufacturing & Operations

Engineering

MACHINE FUNCTION

PITCH DISTANCE

The unit for “p” will be metres (m) f m/min m minp = ---- = --------- = ----- 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 24p = ------- = ------------ = --------- = 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 FUNCTION

MACHINE PROCESSES: CHIP FORMATION


MACHINE SAFETY AND USE


Continuous improvement


RISK MAGNITUDE


RISK ASSESSMENT

Chip breaking aid and pressure bar prevent riving and splintering


MACHINE PROCESSES: CHIP FORMATION

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


GrindingThe grinding angle of a cutter can vary between 30

to 35This is increased to 40 for hardwoods (cutting edge

lasts longer)

OverheatingMay 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 projectionChip breakerKnife parallel to tableAll knives in the same peripheral cutting

circle(Refer to machine manual for setting)


MACHINE MAINTENANCE

Setting devicesThere 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. Cutters require accurate setting in the block because if the knives are not revolving in the same cutting circle a poor fi nish will be produced.


MACHINE MAINTENANCE

MACHINE PARTS: THICKNESSER

MACHINE PARTS/USE: THICKNESSER


RISK MAGNITUDE


RISK ASSESSMENT

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 PARTS: RIP/PANEL SAW

MACHINE DESIGN: SAW BLADE

Hook AngleEdge

ClearancePitchGulletPlate TensionRiving KnifeTable SlotGuardsFence


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 ripping blade will have a Flat Top Grind (FTG) for fast cutting with the grain.

A cross cut blade will do the best job with an Alternating Top Bevel (ATB), cutting across the grain like a knife and producing a very smooth cut. A blade with Triple Chip Grind (TCG)

is good for all-purpose cutting and also gives you a very 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 eff ort 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 alters from the top plane of the timber where the tooth top makes fi rst 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 very 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 very low or negative hook angle, to inhibit overly fast feed rate, binding, and the blade's tendency to try 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 eff ect of sawing Heating eff ect 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 portion of the energy expended in cutting will unavoidably be converted to heat.

The periphery of the blade will therefore tend to warm up more quickly than the main plate body.

This will cause the periphery of the blade to expand. If this is not taken into account the blade will distort. To prevent this saw blades are ‘tensioned’ during the

manufacturing stage. Rim speed will determine the amount of tension required

in a particular 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 rollers 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 after the machine is switched off.

If this is the case the blade should be removed and sent for servicing.

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: TABLE SLOT

MACHINE DESIGN: RIVING KNIFE

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 eff ects of material rejection.

MACHINE DESIGN: BLADE GUARD

MACHINE DESIGN: RIP FENCE

Rip Fence Setting

MACHINE DESIGN: RIP FENCE

RIP-CUT CROSS-CUT

SETTING

MACHINE FUNCTION: CALCULATIONS


RISK MAGNITUDE


RISK ASSESSMENT

wt5912 2012 u2-w3

Education

cutter knives

planer knives knives

cutter block material

knife cutter geometrybevel

lip angle angle

planer knives tungsten

knife cutter geometry

cutter circleknife diameter