wt4603 unit4 week5_03-10-2011

WT4603 Wood Processing Safety & PracticeAutumn 2011Lecture Unit 4 (Week 5)

Circular Saws, Routers & Effective Poster Design Lecturer: Mr. Joseph Lyster [email protected] Notes prepared by: Mr. Joseph Lyster Notes available on www.slideshare.net/WT4603

mailto:[email protected]

http://www.slideshare.net/WT4603

Circular Sawing MachineNOTE 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)

Department of Manufacturing & Operations Engineering

WT4603

HazardsOperators should be aware of the following hazards.

a) The work piece can become jammed in the circular sawing machine or can kick back.

b) Hands or fingers can come into contact with the blade.c) Wood dust can be inhaled.d) Noise can cause permanent hearing damage.e) Inadvertent starting of the machine can present a

hazard.


WT4603

Risk control measuresIt is essential that the machine be provided with:

•A means of electrical isolation using a fused switch-disconnector on or adjacent to the machine, and that it is controlled by a starter incorporating overload protection and no-volt release

•A conveniently positioned, mushroom-headed stop button or suitable other control device that can quickly stop the machine in an emergency


WT4603

Risk control measures• Fixed guards (removable only with the use of a tool), or

alternatively interlocked guards that encloses the drive mechanisms.

• It should be possible to lock the machine to off when not in use, if a locking device is not incorporated in the machine.

• There should be sufficient space around the saw bench so that the timber can be handled safely. The floor of the work area should be level. The floor surface should be kept free from loose material and should be non-slippery.


WT4603

Saw Blade Terminology

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


WT4603

Hook Angle

Hook Angle


WT4603

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.


WT4603

Hook Angle

Positive Hook AngleDepartment of Manufacturing & Operations Engineering

WT4603

Hook Angle

Zero Hook AngleDepartment of Manufacturing & Operations Engineering

WT4603

Hook AngleIn both Rip and Cross-cutting saws the Hook angle determines

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


WT4603

Hook Angle

• 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 first contact to compress the timber before the tooth point engages, to a plane where the tooth angle and the timber face are parallel.


WT4603

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.


WT4603

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


WT4603

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.


WT4603

Tooth Configuration

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


WT4603

Tooth Configuration

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.


WT4603

Tooth Configuration

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.


WT4603

Tooth Configuration


WT4603

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 effort and leave a clean cut with a minimum of scoring.


WT4603

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.


WT4603

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.


WT4603

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


WT4603

Riving Knife

Note :

The thickness of the riving knife is to be approx. 10% thicker than the plate of the saw blade but must be less than the saw kerf “B”.

The riving knife must be tapered at its leading edge


WT4603

Riving Knife

Riving knife should not be set higher than the highest point of the saw blade


WT4603

Riving Knife

Max and min distances between saw blade and riving knife.Distances are measured in a radial direction


WT4603

Riving Knife

Shaded area can be included in the riving knife profile

Example 2 reduces the Ø of blade that can be fitted to the machine and has a weak point


WT4603

Riving Knife

When viewed in the direction of the blade edge the riving knife should not be visible to the operator.


WT4603

Table Slot

Table slot width max. and min. measurements for saw blade ranges.Min. and max. measurements for distance from blade face to edge of table slot.


WT4603

Table Slot

Max. distance between saw blade and front edge of table slot.(Blade raised to highest level)


WT4603

Table Slot

Max. distance between saw blade and front edge of table slot on machine with a scoring blade.(Blade raised to highest level)


WT4603

Clearance

The supporting body of the cutting tip is ‘relieved’ or ground back (X) so that only the cutting edge itself makes work contact.

For any machine cutting tool to work efficiently, only the cutting edge of the tool should be making contact with the work.


WT4603

ClearanceWork 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.Department of Manufacturing & Operations Engineering

WT4603

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.Department of Manufacturing & Operations Engineering

WT4603

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.


WT4603

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.


WT4603

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.


WT4603

Top 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 effects of material rejection.


WT4603

Top Guard


WT4603

Blade Guard

Blade guard that completely encloses the blade


WT4603

Blade Guard

Guard not connected to riving knifeGuard has lead in at the frontDust extraction integrated in the guard


WT4603

Fence


WT4603

Circular Sawing Machines

• Scoring blade rotates in the opposite direction to the saw blade

• Scoring blade cuts on the up stroke of the cut to ensure a clean cut is produced on the underside of the panel


WT4603


Work being fed into the bladeBlade rotates clockwise(Guarding not shown)


WT4603


Top surface – fibres being compressedBottom surface – fibres being ripped outWill damage the under side of the material


WT4603


Top cutting “into the wood”Bottom “cutting out of the wood”


WT4603


Scoring blade introducedWill make an initial shallow cut before the larger saw blade will cut the material


WT4603


In this diagram the scoring blade rotates in the same direction as the saw bladeIs this blade still cutting “out of the wood” on the underside ?


WT4603


Here the scoring blade revolves in an anti clockwise direction. As the material passes this blade the cut produced is “into the wood”


WT4603


• This can create a hazard as the blade is unguarded and tends to pull the material towards the saw blade

• Should only be used when crosscutting or ripping sheet material where a clean finished cut is required on both surfaces of the panel


WT4603

Calculations• Saw Calculations

• Rim Speed (P) = x x Spindle Speed (R)

• Where P = Rim SpeedR = Spindle Speed = Diameter in metres

• Units = m x 1/min = m/min

• This speed is expressed in metres per minute m/min• It is left in this format because spindle speed is expressed in

Rev/minDepartment of Manufacturing & Operations Engineering

WT4603

CalculationsProblem 1

A saw blade of 750mm is required to run at a rim speed of 3048m/minCalculate the number of revs per min that will achieve this speed.

P = x x R P 3048

R = ---------- = ----------------- = 1294.3 RPM x 3.142 x .750


WT4603

Calculations

• Problem 2

• A circular saw has a motor that revolves at 1500 Rev/min• The of the blade is 720mm.

• Calculate the rim speed for the blade.


WT4603

Saw Parts•Guard•Fence•Blade•Riving Knife• In feed table•Out feed table•Start / Stop•Foot stop


WT4603

Blade Guard


WT4603

Fence•Must be parallel to the

saw blade•Clamping mechanism

cam screw lock

•Sliding fence Horizontal position Vertical position


WT4603

Fence (Horizontal Position)


WT4603

Fence Position for cross-cutting


WT4603

Fence (Vertical Position)


WT4603

Fence position for cross-cutting


WT4603

Incorrect setting


WT4603

Incorrect setting

• Material once cut is positioned between the rotating blade and the fixed fence

• When the piece is moved by operator or vibration it will contact the moving blade and get ejected

• This will result in possible injury to the operator, damage to the blade and damage to the material


WT4603

Riving Knife


WT4603

In feed table


WT4603

Out feed table


WT4603

Start / Stop


WT4603

Foot Stop


WT4603


WT4603


WT4603

RECAP


WT4603


WT4603

Cutter selection & feed direction


WT4603

Hand Router


WT4603

•Cutting grooves•Cutting rebates•Cutting slots and recesses•Cutting beads or mouldings•Cutting dovetails•Cutting dovetailed slots and grooves•Edge trimming•Profiling (jigs/formers)

Hand Router


WT4603

• Large powerful routers are heavy and can be difficult to handle for light work.

• Generally in schools the type of work that the router will have to perform will be light to medium work.

• As a rough guide to classifying routers: 400 W to 600W are for light duty 750 W to 1200W are for medium duty 1250 W upwards are for heavy duty

Hand Router: Power

Speed

Machine speed can range from about 800 to 30000 rpm.

Nearly all modern routers have variable speed motors, the setting is by a simple numbered knob showing up to 5 or 6 positions.

The required speed will depend upon the size of cutter being used and the material being cut.

The appropriate speed setting for any combination will need to be determined by trial and error/experience.

The variable speed control should not be in a position where it could inadvertently be changed while routing.


WT4603

Hand Router•Router cutter (bit) is fitted to a collet on the lower

end of the motor• It is a direct drive system•Motor sizes can vary from ½ horse power to 3½ horse

power•The bigger the motor the heavier the router•Cutter profile will often determine the size of the

motor required for the job


WT4603

Hand Router

Collet• Simple but accurate chuck

• Attached directly to the bottom of the motor armature

• Collet holds the bit so that the motor can make it spin

• Two most common size collet are 6mm and 12mm

• 12mm collet will hold a bit with a 12mm shank which is stronger than the 6mm


WT4603

Hand Router• The base of the router is what holds the motor in position in

relation to the work• It usually incorporates two operating handles• Handles used to control the machine• Can be used to lock/release depth plunge• Can contain on off switch• Base plate of the router is a plastic sole on the bottom of the

base• Reduces frictional contact with material


WT4603

Hand RouterMotors rated on their horse power

Will also have an amperage rating

• Determines the maximum amount of current the motor can draw in continuous use without overheating and burning out

• Routers may have the same horsepower rating and different amperage rating

e.g. 1 ½ hp drawing 8 amps1 ½ hp drawing 10 amps


WT4603

Hand Router

• Router motor is of the universal brush type which is primarily used for intermittent, variable speed operations

• Induction motors (brushless) are primarily used for long term fixed speed operations such as the circular saw etc.

• This is the reason why a 1 ½ hp router motor is much smaller than a 1 ½ hp circular saw motor


WT4603

Cutter Speed

The router is a high speed cutting machine

• Generally it is taken that the higher the speed the smoother the cut

• However if the cutter diameter is increased the peripheral cutter speed increases which can make the machine hard to control and prone to damaging the material

• Can also lead to burning of the wood and blunting of the cutting edge


WT4603

Collet• Like a drill chuck it is designed to hold a round shank bit

• The collet makes almost full contact with the cutter shank unlike the three fingered shank of the drill chuck

• Router bit shanks must be sized to match the inside diameter of the collet

• Collet must hold cutter while revolving at high speed

• Must also be able to resist side loadingDepartment of Manufacturing & Operations Engineering

WT4603


WT4603

Feed direction• If you feed a router into a piece of

material without using a guide fence or bearing guide you will find that the router will pull to one side.

• If you push the router into the material from position (A), the router will pull to your left.

• If you pull the router into the material toward you from position (B), the router will pull to your right.

• This occurs as the cutter will climb on the material in front of the cutting edge.

• This motion must be utilised when using guide fences.


WT4603

Feed direction & the fence

To process a straight housing or trench you can use a straight edge guide (A) or the guide fence that is supplied with the router(B).


WT4603

Feed direction & the fence• In the photo the fence is securely

clamped in position.

• The router is being fed in the direction (F).

• The router will try to pull to the operators left hand side.

• With the fence clamped on the left of the router, the router will push against it as it is fed into the material.(Green arrows)

• If the fence were on the right hand side (when viewed from the operators position) of the router, it would pull away from the fence and result in the trench being crocked.

F


WT4603

Feed direction & the fence• The groove is produced as the router is

moved forward.

• Local extraction will remove the bulk of the dust produced.

• Some may be blown back in the direction of the operator.( )

• A suitable lab coat will protect the operators clothing.

• Appropriate dust mask should be used.

• Feeding the router in the opposite direction will cause any dust to be blown away from the operator.

• This will require the guide fence to be set up on the right hand side of the router and operator.

F


WT4603

Guide fence

Guide fence fixed to the router.Can be fixed from either side.


WT4603

Using the guide fence

F

P

When feeding the router forward (F) the router will tend to pull to the operators left hand side.

The fence should be set on the right hand side of the router.

When the cutter engages in the material it will pull to the left as indicated by the green arrow (P) and keep the fence tight against the materials edge.

Material should be securely calmped or placed on a non-slip router mat.


WT4603

• Profiles can be processed on material using templates.

• Templates can have the required profile as an internal shape or an external profile.

• To process the section marked (A)

• In the photo an internal template can be used to guide the router to produce the profile.

• Feed direction can be established using the right hand rule.


WT4603


WT4603

Fit the template guide to the router base plate.Set cutter plunge depth.Place over template at the starting position (A).Switch on the router and then plunge to depth (B).Feed router in a clockwise direction.

Using the template guide

Router Station 1Carry out the following operations:1. Isolate the router. 2. Select V- groove cutting bit.3. Fit the bit in the router securely.4. Set the depth of the cut to 3mm.5. Machine the profile shown on the drawing

using the guide fence. (Note: Guide fence is set. Do not adjust.)

6. Isolate the router.7. Remove the cutter from the router.

FEEDDIRECTION

ROUTER PULLS TO THE LEFT

FENCE PULLED TOWARDS

WORKPIECE


WT4603

Router Station 3Carry out the following operations:

1. Isolate the router.2. Select Ø 6mm cutting bit.3. Fit the bit in the router securely.4. Set the depth of the cut to 5mm.5. Set the depth turret to machine to a depth of

10mm on the second pass.6. Fit the guide fence to the router.7. Set the guide fence to the dimension shown on

the drawing.8. Machine the profile shown on the drawing using

the guide fence.9. Isolate the router.10. Remove the guide fence and Ø 6mm cutting bit

from the router.


WT4603

Router Station 4Carry out the following operations:

1. Isolate the router.2. Select Ø 12mm cutting bit cutting bit.3. Fit the bit in the router securely.4. Fix the template guide to the base of the

router.5. Set material in the template.6. Set the depth of the cut to 5mm.7. Set the depth turret to machine to a depth of

10mm on the second pass.8. Machine the profiles of the template using the

template guide.9. Isolate the router.10. Remove the template guide and Ø 12mm

cutting bit from the router.


WT4603

Designing An Effective Poster


WT4603

Function & Sizing


WT4603

• Posters must present information in a clear and coherent manner for user interpretation

• Posters vary in size depending on the purpose and space where it must be displayed

• Posters ranging from sizes A1-A3 are ideal for classroom settings

• In the case of this assignment you are required to produce an A2 poster

• It can be configured in either landscape or portrait orientation

• Student name and ID. must be visible on poster.

Graphics


WT4603

• In this case graphics are to be hand-sketched• Graphics must be sketched in proportion to the A2

page with enough room left to present supporting text• It is suggested that the largest graphic be placed at

the centre of the page• Graphics must be sketched neatly using no less than a

HB-2B pencil or a pro-marker if so desired.• Render appropriately i.e. shading or/and use of colour • The use of safety signs, as visible in lab, is also

encouraged but must be hand drawn and rendered.

Text


WT4603

• A poster must be readable from a distance of at least 3-5 metres, therefore the font size of text and size of graphics is very important.

• Poster text should be produced electronically, unless it can be presented clearly through other means.

• Hand written text is often ineffective unless technical print text is performed with care, which is also acceptable.

• The positioning of text is crucial in this poster assignment as you want to make it relevant to machine parts, operational use and health and safety.

• You may also apply the use of a key legend as a means to linking poster features with user information/activity sheets.

Colour


WT4603

• Different colours have been proven to encourage certain types of behaviour, for example:

• Blue = Mandatory/Information• Green = Safe/Perform Action• Red = Prohibition/Do Not Perform Action• Yellow/Orange = Danger/Warning/Caution

• The specific use of colours should be evident in the design of your safety posters

Background


WT4603

• Safety posters are primarily information posters so the use of colours such as blue should draw the user’s attention to the information given.

• In the case of this poster assignment it is suggested that blue is used appropriately, but not for the entire background…as this will waste ink and prove costly in terms of printing.

• It is suggested that a clear-white background be used with text information being presented in different colours, in particular instructional information (blue)

Layout


WT4603

• Similar to graphics, it is important that all items are arranged effectively on the poster.

• People tend naturally to view poster items in a clockwise manner unless there is a clear distinction of items on a given poster i.e. number sequence, separation of text and images/graphics, headings, sub-headings etc…

• This poster is pre-dominantly for classroom use for ages ranging from 13-18yrs of age, therefore a safety posters for any machine should be arrange in a simple and easy to follow manner

Methods of Producing a Poster


WT4603

1. Produced by Hand• All features/items produced by hand using pencils, pro-markers, etc…• Cut out/Stick on items are also a viable option, including printed text if

so desired. 2. Produced Electronically

• Use of electronic pro-sketch/ 3-D parametric modelling packages to produced items

• Text applied electronically through use of word/powerpoint/adobe photoshop of A2 configuration

3. Produced Using a Combination of Hand/Electronic• Sketched images are scanned into word/powerpoint/adobe of A2

configuration• Text applied electronically• Items arranged electronically

Example of Simple and Effective Poster


WT4603

Produced by Mr. Brendan Scally 08/09

wt4603 unit4 week5_03-10-2011

Education

joseph lyster

lecture unit

circular saws