HARVESTING EQUIPMENT, PREPARATION AND MAINTENANCE
|Contents - Previous - Next|
6.1 Machine Shearing
6.1.1 Harvesting Equipment
Although the modern handpiece appears to be a solid piece of machinery, it is a delicate precision tool.
The outer casing is a steel casting carefully machined to very fine tolerances, while moving parts are formed from specially hardened steel.
22.214.171.124 Setting Up The Handpiece
Select the most suitable comb for the job. Ensure that the comb and cutters to be used are properly ground.
Make sure the comb bed of the handpiece is properly cleaned. Place the comb on the handpiece and set it with the ground fact against the comb bed using one of the comb screws to secure it for the moment.
Turn the handpiece right side up and slip the cutter under the forked yokes, ensuring the pins sit in the holes in the cutter. Apply just enough tension to stop the cutter falling out.
Now adjust the position of the comb to get the correct lead and throw. The cutter should extend far enough each side to just cover the outside teeth on the comb. Secure the comb again so it will not slip.
Check again that the cutter is not placing any pressure on the comb before finally tightening the comb screws.
Recheck the lead and throw, then apply shearing tension to the cutter. The tension can be "fine tuned" when the handpiece is fitted to the dropper and the machine started. The handpiece should just turn in your hand when you relax your grip.
Note: Lead should never be less than 2 mm.
Insufficient lead is the main cause of skin cuts. Always use more lead in full wool, fine wool or when using thinner combs.
Figure 6.2 Lead
Note: If the tension is too loose it might be dangerous as the cutter may fly off or lock up the handpiece. It may also allow the wool get between the cutter and comb and will not then cut effectively, even if subsequently tightened. If the tension is too tight the handpiece will overheat and cause excessive comb and cutter wear.
The body or barrel of the handpiece contains one small oil reservoir which may need filling with clean grade 30 oil every two hours. At the same time, put a few drops of oil on the comb surface, the fork yoke sleeves, the tension pin cup, the crank roller and a squirt of oil down the ferrule on the back joint.
Periodically putting grease in the tension sleeve should complete an adequate lubrication job.Note: Do not put grease inside the tension nut.
Any sign of overheating around the tension nut will signal a lack of lubrication. Similarly, overheating around the post can generally be fixed by placing a drop of oil on the centre post.
126.96.36.199 Fault Finding
It is rare that a handpiece malfunctions except as the result of an accident which has damaged it. But there is a gradual deterioration in performance over time as the working parts wear.
Ninety percent of supposed handpiece malfunctions are due to poorly ground gear. First ensure that your combs are evenly ground over the whole surface with no white hairlines visible on the cutting edges. Cutters must be evenly ground over the whole surface with no dull tips.
These partially ground edges show up as dull tips or white hair lines on the edges of the teeth.
Figure 6.3 Cutter
Check the performance of the handpiece with properly sharpened gear before taking any other corrective measures.Next remove the comb screws, clean the comb bed and visually check that the comb bed is perfectly flat. Also check there is no wool caught in the cups. Ensure the fork yokes swivel freely in the fork.
If none of the above faults are evident it may be time to replace any worn parts.
Look for white lines on the cutting edges. These are actually rounded edges not quite ground out. Also check that there are no score marks on the combs. If faults are apparent repeat procedure.
188.8.131.52 Replacing Parts
Figure 6.5 Parts requiring regular replacement
There are some parts of the handpiece that require regular replacement. After wearing out a string of 50 cutters, which is the normal number a professional shearer would carry per handpiece, you should replace the tension sleeve, the tension pin and top cup. The centre post and bottom cup should also be replaced.
Fork yokes, back cogs, joint guard and drive pin will require periodic replacement.
There are three essential safety parts on any handpiece. NEVER operate a handpiece without them. They are there for the shearer's protection. They are the tension spring, the fork yoke retaining bar and the tension pin retaining spring.
The tension spring should be working properly, stopping the tension gradually coming off. Without the spring unnecessary tension is often used and accelerates the speed at which gear wears, requiring a major gear grinding job.
If a new spring is too tight, remove it and squeeze it up before refitting. This will allow it to retain tension without making it so tight that it makes changing cutters difficult.
Figure 6.6 Parts requiring periodic replacement
Fork Yoke Retaining Bar
This bar is designed to secure the fork yokes to the fork.
Tension Pin Retaining Spring
This simply holds the tension pin in place. The handpiece is unsafe to use without it in place as the pin could slip while changing cutters. Note: Absence of an effective tension spring will contribute to lockups.
Figure 6.7 Essential parts
It is dangerous to operate any handpiece without them.
Centre Post and Cup
With normal use the back of the post wears against the back of the bottom cup to form a smooth complementary pivot surface. Once this surface is created, it is most important that the post is not moved from its original working position.
The only time the post should be adjusted is when you are installing a new post and bottom cup. You would normally replace the centre post and bottom cup when you are setting up a new supply of cutters.
With the handpiece set up with a comb and half worn cutter the correct setting is when one third of the crank roller is visible above the fork body when you look down the barrel from the cutter end. On a new handpiece the centre post is normally correctly set but should be checked.
Once it is bedded into the cup the centre post SHOULD NOT be adjusted.
Worn post and cup
Do not adjust post once it is worn
Figure 6.8 New post and cup
The Comb Bed or Baseplate
The handpiece is a piece of precision machinery which can be easily distorted by rough treatment. Constant dropping on the floor, being kicked from the shearer's hand to smash against the wall or other maltreatment can bend the comb bed. This is a serious fault and is best fixed by sending the body of the handpiece to a suitably equipped engineer or agent who specialises in handpiece repairs.
A correctly aligned bed will be parallel to the screw bushing and at 90 degrees to the tension bushing.
|Comb bed and tension bushing should be at right angles.
Comb bed and screw bushing should be parallel.
If the comb bed is damaged, it must be repaired by a qualified shearing engineer.
184.108.40.206 Safety Tips
Do not operate the handpiece with badly worn fork yoke pins or when the fork yokes are sloppy inside the fork sleeves.
Do not start the handpiece without checking that:
- The comb screws are firmly tightened (note: excessive tightening will eventually strip threads in the handpiece body).
- The fork yoke pins are securely located in the cutter holes.
- The correct starting tension is applied. Using the thumb on the back
cogs, move the cutter across the surface of the comb. A safe
starting tension will leave a good impression of the cogs on your thumb.
220.127.116.11 The Spline Drive/Pin Option
The traditional connection of the handpiece onto the down tube has been a pin drive. Another option which is becoming popular with some shearers is a spline drive.
This has an important safety benefit if the shearer hits an ear tag, piece of wire or the handpiece locks up for some other reason.
When operating with a spline drive, the handpiece usually unlocks from the gut before any serious damage occurs. With a pin drive, a lock-up will normally result in expensive breakages and possible loss of work through injury.
Many machines are not fitted with spline drives. Safety conscious shearers can overcome this by carrying their own appropriate short gut and fitting it into the machine before they start. Don't forget to retrieve it at the end of the job though!
18.104.22.168 Dressing a New Comb
Dressing a comb should always be done in good light and involves shaping the teeth to the ideal profile. This should be done before the comb is ground and requires three stages.
1. Shape the bevel to the desired profile using a piece of fine emery working from the back of the comb over to the cutting face aiming at a high rounded point. There are three common faults which should be avoided:
(A) Too round: will not enter the wool properly and tends to ride out of the wool.
(B) Dropped point: with a tooth of this shape skin cuts will occur.
(C) Squared off points: will not enter the wool easily and skin cuts will occur.
(D) The correct shape: the most
important part of dressing a comb is the finish. All teeth must be dressed to the same
must also follow an even concave.
2. When the bevels are finished, the next step is to fine the bottom edge of the bevel (the edge that runs along the skin) down to approximately the thickness of the edge of a postcard.
Good fine teeth mean better combing. Using a fine wedged slip stone, emery or a tapered spinning disc grinder called a bright boy, start from the back of the tooth and work around to the point, taking care not to alter the point which has just been formed nor to go too far and damage the cutting edge of the comb. DO NOT OVERTHIN.
As illustrated, if the teeth have not been thinned, they will ride off the skin causing second cuts (A);
The comb best suited to quality work is where the tips have a fine white line around the end of the tooth (B);
Over thinning will cause skin cuts (C).
3. To get a smooth finish, use 1200 grade wet and dry sandpaper then check bevel fineness to make sure all the teeth are of the same thickness.
Polish the teeth by rubbing on a leather strap, an old rubber tyre or a machine buffer. Use polishing compound for a good shiny finish. Polishing combs helps to stop the greasy building up and allows for smoother entry and running.
When you've completed dressing and polishing combs grind them ready for shearing.
Figure 6.10 Common Faults
Figure 6.11 Thinning the teeth
Figure 6.12 Comb Tip
Dressing a Worn Comb
When combs are ground down so that the scallop grinds out and they become too sharp to use, repeat the process for dressing a new comb.
Each time the comb grinds out to a sharp tip, redressing is required. The teeth get shorter and slightly rounder each time. Note: Be careful not to sand along cutting edges.
Grinding is an extremely important part of shearing. It requires a high degree of precision and care. Shearers often blame their handpieces, the sheep or themselves for their difficulties. Often poor grinding technique or faulty machinery can be the cause.
- The grinder should be placed away from doorways and steps.
- It should be in a well-lit area with easy access for grinding.
- Never leave the grinder running unattended.
- Check the pins on the pendulum for length.
- Guards must be fitted to the grinder.
- The use of safety glasses is essential. (Carry a pair in your tool kit).
- Always check nuts are tight before turning grinder on.
Note: A grinder can be lethal. Do not rush when grinding, use common sense and safety equipment - for your own sake and the sake of others in the shed.
|Top magnetic bar is slightly
shorter than lower pressure bar so that the heel of the comb or cutter always
touches the disc first.
Figure 6.13 The Pendulum
|Bottom view of the pendulum
bar showing corners ground off. This will prevent an accurate grind.
Figure 6.14 A damaged holder will not grind properly
The exclusive use of a good pendulum on a correctly set grinder will ensure reliable and efficient grinding at all times.
The bottom bar of the pendulum applies pressure to the comb or cutter during grinding and it is essential that it is true. If the bar has the corners ground off, it will not give an accurate grind.
The recommended setting between the pressure bar and pins is 4 mm; a closer setting will heel grind; a wider pin setting will tip grind.
Make sure that the pins are long enough so that they maintain a hold on the comb or cutter.
- When not in use store so that the pendulum rod does not bend.
- Use a metal strip on the magnetic bar to retain magnetism.
Heel grinding results from use of pendulums where the pin settings are closer than the recommended 4 mm. To avoid tip grinding a small bevel may be removed from the heel of the comb.
Excessive heel grinding is not recommended because it:
- Prevents sufficient grinding pressure being applied to the tips of
the comb to sharpen cutting surfaces properly.
- Creates excessive flexibility in the heel of the comb.
- Affects the contact of the comb screws on the comb.
The Hollow Grind
The face of the grinder disc is shaped to give a very slight hollow grind between heel and tip of combs and cutters. This is essential to bring the cutting edges of the comb and cutter together properly under pressure.
The height setting of the pendulum is very important to produce the hollow grind on the face of the comb or cutter. When the pendulum rod is handing straight, a vertical flow of sparks from the tips will indicate the correct settings.
Using the hook to suspend the pendulum, the heel of the comb or cutter should touch the disc just before the tips. With the pendulum hanging straight, the magnetic bar should hand 25 mm from the outer edge of the disc.
The Disc has a half degree fall from centre to edge.
This produces a hollow grind in the gear from heel to toe.
22.214.171.124 Grinding Procedure
Combs should be ground on the coarse paper (40 grade) with the bottom tooth of the comb towards the outside of the disc. After ensuring the pins of the pendulum are in the holes of the comb, put the comb to the disc. Using a firm even pressure move the comb five or six times (six to eight seconds) across the paper, making sure it does not run off the edge or into the centre of the disc. Before removing the comb, hold it still with an even pressure for 2-3 seconds with the pendulum rod straight.
- Ensure that the sparks are even right across the comb.
- Remember too much pressure overheats and distorts the comb.
After grinding, check combs by looking across the teeth from side to side in good light.
The HEIGHT SETTING of the pendulum is
therefore MOST IMPORTANT.
A vertical glow of sparks indicates the ideal setting.
Pendulum rod must hand parallel to disc with the heel of the comb or cutter touching first.
Edge of magnetic head should hang 25 mm from edge of disc.
Pins must swing just under the centre of the shaft for cutters and to the bottom of the shaft for combs.
Combs: Cross section of one tooth, shows original sharp edge rounded with use.
Figure 6.18 Worn combs
Follow the same procedure as with combs using an even lighter pressure and reduce to two to four passes (3-4 seconds) across fine paper (80 grade).
Cutters should be ground evenly over the whole surface with no dull tips. If there are any faults repeat procedure.
Should be ground evenly over the whole surface with no dull tips or white hair lines on the edges of the teeth.
Figure 6.19 Cutters
Check that cutters are grinding down evenly on both sides. Also ensure that each cutter is wearing at the same rate. Rotating on a wire or cutter holder will help. The handpiece will work better and last longer if the cutters wear down at an even rate. For a full time professional shearer a string of 50 cutters is recommended.
If there are any faults after the check repeat the grinding procedure and recheck.
126.96.36.199 Grinding Equipment
Always store papers in dry conditions. Ensure that the disc is clean, free from old glue and dry. Place new paper on clamp. Spread glue onto the disc evenly and sparingly, then clamp the paper firmly but without excessive pressure. A thin flat sheet of cardboard between the emery and the clamp will reduce the crushing of the emery grit.
Care of Papers:
Do not grind first thing in the morning or when the atmosphere is damp. When the papers are partly worn they can be revived by using a rubber cleaning stick and a light stroke with a carborundum stone or wire brush. Light, even grinding will also make papers last longer.
Although discs are made of cast steel, they can be distorted by rough treatment or wear and tear.
- When not in use for long periods store discs on the clamps.
- Check that the back of the disc and the area where it connects to the grinder are clean when mounting discs.
- The centre of the paper should be cut out and any excessive glue cleaned away.
- Always use washers when setting paper and mounting discs on grinder.
- These machines are for sharpening shearing gear and should not be used as bench grinders.
- Discs in need of repair can be refaced and rebalanced by engineers specialising in shearing equipment.
Note: For best results, use your own grinder all the time or carry your own discs from shed to shed. Always use your own pendulum.
6.2 Hand Shears (Blades)
A new set of blades may appear sharp enough for general purposes, but a good deal of attention is required before they can be used.
The sharp edges necessary for successful shearing, will be maintained for a longer period if the blades are properly set. If any alterations made, it is always necessary to maintain as far as possible the makers' "set".
6.2.1 Pulling Back (for separating the blades)
Pulling back is carried out so that the shears will take more wool in each cut. The amount of opening up will vary according to the individual shearers and the type of fleece being shorn. In hard-cutting wools with little or no rise of the yolk, less wool should be taken than in open fleeces or those with a good rise.
If the shears are to be used for dagging only, it may not be necessary to pull them back at all. They are then less dangerous, especially to those not accustomed to using them.
There are several methods of pulling shears back. In all methods care must be taken to prevent twisting and warping, especially when using a vice. The pull must be even on each blade, so that the makers' set is maintained and no bend is put on the blade. In one method, each handle in turn is gripped in the vice, and the pull is straight back toward the operator. Another methods uses a small block of wool nailed onto a wall stud, above a dwang (Fig. 6.20).
Correctly pulled back blades should be about 30 mm apart at the tips, when fully closed.
Figure 6.20 Pulling
Figure 6.21 Adjustment
To adjust the shears, one of the blades is cut out with a hacksaw and filed so that a spike is shaped to impale a piece of 6 mm leather (knocker, see Fig. 6.21). The knocker prevents jarring, and eliminates the metallic noise when the blades come together.
When the knocker is pressed into place, the blades will not close fully at the points. This is corrected by cutting or filing the shoulder of the opposite blade until the points almost meet. Do not overdo this as the points must not overlap.
This is done in a vice. Secure the back of one blade horizontally in the vice, with its cutting edge upward. The blade is then bent one way or the other from the bow end so that, when closed, the rear cutting edge of the lower blade is 1.5 mm away from the top inside edge of the upper blade. The other blade is then set in the same way.
Figure 6.22 Setting
Figure 6.23 Grindingt
6.2.4 The Grindstone
A sand grindstone is used initially, to bring up an edge on each blade. This can then be finished easily and quickly with an oilstone.
The grindstone surface should be level. If there are bumps or hollows in the middle, they must be taken off by grinding against a heavy, sharp-edged piece of metal. Sometimes a small, hard flint or stone appears in the he surface. This can be carefully chipped out to prevent denting (gapping) the edge of the blade.
Water only is used to lubricate a sandstone. Any oil or grease contamination on stone or shears must be removed before grinding. Grease will fill up the pores of the stone, preventing good abrasion and making the stone slippery and dangerous.
The amount of water should be just enough to keep the stone nicely wet. Too much water will wash off all the surface grit that helps grinding, and a dry stone will burn the metal in the shears or take the temper out of it, leaving a soft spot that will not hold an edge.
6.2.5 Grinding The Blades
The blade is held at about a 10 degree angle to vertical. The marker's edge (the edge left by the manufacturer on a new blade) should be almost ground off. DO NOT OVERGRIND. The finished bevel should be as flat and level as possible and approximately 4 mm wide. After grinding, wash and dry blades thoroughly. Care must be taken not to hollow the grindstone out. When the stone gets a hollow in it, use an old file held across the stone to level it out again.
6.2.6 Grinding with a Bat
The ideal grinding technique is with the use of a bat. The blade is held in the bat and moved across the stone giving a hollow grind. Care must be taken not to grind the blade too thin. A white line should be clearly visible along the length of the blade. Remember, on a smaller grindstone you will get more of a hollow grind. Grinding with the bat is safer, gives a better grind and keeps the grindstone much flatter.
Traditional sandstone grindstones are not as common today as a few years ago, largely replaced by electric bench grinders.
You can use a 150 mm bench grinder using a white stone to grind your shears. However, care must be taken not to overheat the blades.
Figure 6.24 Grinding with a bat
Figure 6.25 Sharpening
6.2.7 The Oilstone
A number of different types and grades of oilstone are available. The oilstone must be looked after. Some hints on the care of an oilstone are:
r It is very brittle and should never be dropped.
r It must be kept clean of dirt
and congealed oil. A dirty stone should be boiled with washing soda and a little soap
makes carry directions to clean them with kerosene).
r The cutting face must be kept
flat. If it has a hollow (which it will slowly get), it can be levelled again by being
ground on the sand
grindstone or by being rubbed with coarse emery paper on a flat surface.
It should be oiled regularly with a thin, clear oil. An oiled rag can be placed under the stone. When the stone is picked up it will have a film of oil adhering to it, and when it is put down, the oil rag will take off any particles of dirt, dust and fine metal.
An oilstone should not be used on wet shears, because there is a danger of the stone slipping off the blade.
Using a fine carborundum or soft Arkansas oilstone hold the blade open at chest height on a 60 degree angle in the end slot of a sharpening peg. Using the slot, keep the blade steady and the angle constant. The stone is applied at a 45 degree angle to the blade and lightly rubbed with a smooth circular motion toward the operator. When there is a thin even line along the cutting edge, stoning is complete except for removing any feather edge which may be on the inside of the cutting edge.
Lay the stone flat across the inside of the blade and stroke gently from the back to the tip of the blade once or twice. To test if blades are sharp, place a staple of wool between them and cut. If the wool runs towards the tips, the blades are still blunt and more stoning is required.
6.2.9 Spring Tension
If the shears spring open too far, the spring can be weakened by placing the bows of the fully closed shears on the floor at a 45 degree angle, inserting a file in the bows and pressing down. Turn the shears over and repeat.
The blades should spring open so that the heels just meet. Make sure the bows are always centred in the middle of the handles when closed.
Figure 6.26 Spring Tension
Figure 6.27 The driver
6.2.10 The Driver
Shears should be equipped with a driver, otherwise there is a great risk of permanently injuring a hand, especially if the shears are pulled back.
A driver may be made of strip of leather which is soft and pliable, but which will not stretch. The uses of the driver are:
r To push the blade into the wool.
r To prevent the hand slipping up over the blades.
r To give assistance in guiding the shears while the hand is opening and closing.
r To prevent the shears being knocked or kicked out of the hand.
The driver can be bound to the forward end of the top handle, turned over the back of the hand, and tied back to the centre of the bows. Alternatively, it can be brought to the junction of the handle and bow of the bottom blade and half-hitched there with the free end tied securely on the outside of the bows.
|Contents - Previous - Next|