THE WORKINGS, NATURE AND PARTS OF THE MODERN MILLING MACHINE FOR ENGINEERING PURPOSES

Milling machines are very versatile in nature. They are usually used to machine flat surfaces, but can also produce irregular surfaces. They can also be used to drill, bore, cut gears, and produce slots. The type of milling machine most commonly found in student shops is a vertical spindle machine with a swiveling head. A milling machine removes metal by rotating a multi-toothed cutter that is fed into the moving work piece. The spindle can be fed up and down with a quill feed lever on the head. The bed can also by feed in the x, y, and z axes manually. Once an axis is located at a desired position and will no longer be fed, it should be locked into position with the Gibb locks.

Most milling machines are equipped with power feed for one or more axes. Power feed is smoother than manual feed and, therefore, can produce a better surface finish. Power feed also reduces operator fatigue on long cuts. On some machines, the power feed is controlled by a forward reverse lever and a speed control knob.

Trimming the head

The head of a vertical milling machine can be tilted from side to side and from front to back. This allows for versatility of the machine, but these adjustments can drift. Occasionally, one should check and adjust the head so that the spindle will be normal to the plane of the table. 

Install a dial indicator into the spindle so that the dial is offset at least six inches from the axis of the spindle and the indicator probe is facing down. Lower the spindle until the dial indicator contacts the table then registers about one half of a revolution. Set the dial indicator is toward you and set the bezel to zero. Rotate the spindle by hand 180 degrees. If the dial indicator still reads zero, the spindle is aligned front to back. If not, adjust the head until the dial reads half of the original reading and iterate the entire process until the error falls within acceptable limits. Repeat the process with the dial displaced left and right to alight the head side to side.

Squaring of the vise

Work on a milling machine is most often held in a vise clamped onto the bed. To make features aligned with the edges of the stock, it's necessary to align the vise with the feed axes of the mill. To do this, mount the vise on the bed and secure it with T-bolts, but only lightly so as to permit adjustment of the orientation of the vise. Mount a dial indicator in the spindle of the machine with the probe facing away from you. Lower the spindle and run the bed of the table back until the fixed jaw of the vise is in contact with the indicator and further until the indicator registers one half of a revolution. Set the bezel to zero. Use the cross feed to run the indicator across the face of the vise. If the vise is squared, the inductor will remain at zero. If the dial indicator does not read zero, tap lightly with a soft hammer to realign the vise reduce the indicator reading to half of its previous value. Iterate this procedure until the dial indicator reads zero through the full travel across the face of the vise. Tighten down the T-bolts be careful not to change the vise orientation. Recheck the alignment of the vise.

Different types of milling cutters

In vertical mills, milling cutters with solid shafts are usually used. Milling cutters with keyed holes are predominantly for use in horizontal mills. End mills are designed for cutting slots, key ways and pockets. Two fluted end mills can be used to plunge into work like a drill. End mills with more than two flutes should not be plunged into the work as well. Ball end mills can produce a fillet. Formed milling cutters can be used to produce a variety of features including round edges.

Removing and installation of milling cutters

To remove a tool, move the quill to the highest position and lock it in place. Then, engage the brake while loosening the draw bar with a wrench. Ensure that the draw bar's threads are still engaged in the collets. Tap on the end of the draw bar to release the collets from the spindle. If the threads of the draw bar are not engaged, the milling cutter will fall, and could be damaged. Finally, unscrew the drawbar from the collets.

To install a tool, place the desired milling cutter in collets that fits the shank of the cutter. Insert the collets into the spindle. Ensure that the key way on the collets mates properly with the key in the spindle. While holding the tool with one hand, start the threads of the draw bar into the collets by hand. Use a wrench to tighten the drawbar down with one hand while holding the brake.

Climb verses conventional milling

During milling, one should be aware of the difference between conventional, and climb milling. In conventional milling, the work piece is fed into the rotation of the cutter. This type of cut requires lower forces and is preferred for roughing cuts. In climb milling, the work moves with the rotation of the cutter. This produces a better finish. It is not recommended if the work piece cannot be held securely or cannot support high forces.

Calculating speeds and feeds during milling

Cutting speed refers to the speed at which the tool point of the cutter moves with respect to the work measured in feet per minute. Feed is the rate at which the work moves into the cutter measured in feed per tooth revolution. Feeds and speeds affect the time to finish a cut, tool life, finish of the machined surface and power required of the machine.

The cutting speed is mostly determined by the material to be cut and the material of the tool. To find the right speed for any task, refer to the Machinery's Handbook or other reference. To calculate the proper spindle speed, divide the desired cutting speed by the circumference of the tool expressed in feet. The feed rate depends on the width and depth of cut, finish desired and many other variables. To calculate the desired feed setting from the feed rate, multiply feed per tooth per revolution by number of teeth and rpm of the spindle.

Setting of the spindle speed

The setting of the spindle speed is varied by changing the geometry of the drive train. On many modern machines, it can be adjusted continuously with a hand crank. The spindle must be turning to make the adjustment. A dial indicator reads the speed in rpm.

Using an edge finder

Before doing precise work on a milling machine, you must be sure to locate the edges of a part accurately. An edge finder is designed to help you do this. An edge finder is composed of two concentric cylinders, spring loaded together. To use it, offset the two halves slightly so that there is a wobble as it spins. Then, move the part into the tool slowly. The edge finder will center up, and then break out of concentricity suddenly. At that point, reset the dial indicator or digital readout for that axis of the machine to a value equal the radius of the edge finder. Repeat the process at least once.

Using the micrometer dials

Most milling machine manual feeds are equipped with dial indicators. If you know how far you want to feed the bed, you can set the dial indicator to that number (in thousandths of an inch). Just turn the locking ring counterclockwise to free the dial indicator, set the dial, and lock in the setting. Be certain that the backlash in the mechanism driving the table is taken up prior to setting the dial indicator.

Squaring Stock

To create a square corner on a part, first orient an already finished edge vertically in the vise and clamp lightly onto the part. Set a machinist's square against the finished edge and the bottom of the vise. Lightly tap the part with a plastic hammer to align it with the square. Clamp the vise down securely. Now the top edge of the part is ready to be milled to horizontal.

Face milling

In face milling, it is often necessary to create a flat face on a large part. This can be done best with a facing cutter. Select a cutter about one inch wider than the work piece so that the facing can be accomplished in one pass.

CIRCUMSTANCES OF ACCIDENTS, CAUSATION AND EMERGENCIES ON FARM LANDS

Accidents with farming vehicles and machinery aren’t the only causes of injuries and fatalities. Falls from or through fragile roofs are common too in causing accident on the farm land. As it is vitally important to administer first aid as quickly as possible after an accident occurs, you are advised to have some members of staff trained in first aid administration to any occurance of accident. As back and muscle problems can be a major problem in the farming industry, you should make yourself aware of the main causes of these injuries and how they can be avoided

Lifting and handling

Most farming items and tools are very heavy and difficult to move without assistance. Bales of hay, feed bags and other items should be moved by mechanical means where possible, that is using a forklift that is operated by a properly trained personnel in the farm.

Note that it is also your responsibility to ensure that seat belts or lap straps are used when operating lifting equipment such as forklifts or telescopic handlers when working with raised loads. This is especially important when working on any sloping or rough terrain on your farm. Where there is the possibility of equipment rollover, belts or straps are essential for usage. The proper handling of bales or other heavy objects using safe lifting techniques should ensure that back injury is minimized at all times.

Preventing falls on the farm

In the farm during farm operations, falls from height are the second highest cause of deaths and major injuries in current agriculture. You must make sure that all work at height is properly planned, supervised and carried out by people who are competent and have the technical know-how to do the job. You should only use suitable and well-maintained access equipment too in the farm. In the farm, the key issues are:

Working on roofs: Roof work on or near fragile materials should be strictly avoided. You should 

also plan to ensure the right equipment; suitable weather conditions and enough time are available to do the task at hand safely

Stacking and loading: A falling stack of bales can be extremely dangerous to anyone around. You should make sure that staffs are properly trained and adequate equipment is used to secure bales while stacking operation is on.

Ladders: These can easily slip, and there is an extra danger if they lean against a fragile surface. If there is any alternative, such as a temporary work platform or scaffolding, consider using it. You should never undertake long-term planned work at height using ladders. It’s not advisable.

SAFETY AND HEALTH OF PEOPLE IN GENERAL IN THE OPERATIONS OF FARMING ACTIVITIES

Farming activities can pose risks to the health and safety of you and your employees around, and also to any contractors or visitors, including walkers, hikers and cyclists, that may come onto your farm land. Public safety and health should be a part of your overall health and safety policy. In the farm land, it is advisable to carry out a risk assessment; by this act you can minimize any risks to those on your farm land.

Rights of way

If you have people passing through on your farm land, you must minimize any risk of injury which may occur to them. You must take care to make sure that any invited visitors onto your farm land are reasonably safe, and that there are adequate warnings of any danger.

Livestock

If in your farm, an animal injures somebody or causes damage, you may be liable and held responsible for it. If you have fields that are accessible by the public and have livestock normally in them, you must make sure:

• That you do not keep bulls in fields with footpaths around
• That if you keep beef stock bulls in such fields, that they are accompanied by female stock and you put up suitable warning signs around
• That you assess the temperament of any cattle kept in fields with public access, and remove from the group any that may be aggressive among them

Disease control

As a farmer, you have all the responsibility to ensure that you do not inadvertently spread disease from your farm to humans, livestock or plants around. This means you must observe strict hygiene and health standards when storing, transporting or disposing of animal and plant matter. You must also report any incidents outbreak to the proper authorities, and strictly follow their instructions in the event of any disease outbreaks as well.

Open farms

If you open your farm up to the general public, you have certain responsibilities under health and safety law. Responsibility such as taking steps to protect people from harmful micro-organisms in and around your farm land.

Child safety

There are legal prohibitions on children under the age of 13 driving vehicles and machines for agricultural operations, and on children riding on machines, vehicles and farm implements to farming work. Older children of school age and above may undertake some of these activities which are subject to conditions.

Public highways

You should not obstruct a public highway or do anything that could cause inconvenience or danger to the public. This includes leaving compost, dung, rubbish or mud on a carriageway around your farm. Your farm should also include reflective road signs to direct traffic when it comes onto your farm land. Hedges, trees and shrubs should all be maintained to avoid any danger to the visiting public, and you must ensure that any ditches around have proper drainage.

Spray drift

When using pesticides, you must take reasonable precautions to protect human health and safety and the environment at large. Any queries about the use of pesticides on your farm should be directed to the HSE. It is your responsibility to ensure that the general public is not affected by any chemical drift from spraying operations on your farm land.

FARM HEALTHY CONDITIONS AND SAFETY RISK ASSESSMENTS

When it comes to farm healthy condition and safety risk assessments, it is important to be proactive about the health and safety aspects of your farm business and surroundings. All accidents can be avoided if the risks are properly managed. In order for you to identify and so avoid accidents on your farm, it is vital to undertake a risk assessment. This will enable you to see which areas of your farm pose the greatest risk to health and safety. Once you have identified and clarified these potential risks, you can then take practical steps to avoid accidents.

The management of health and safety at work regulations require that all employers or the self-employed assess their own risk, and the risk to anyone working for them regarding their working environment. The law requires you to take all reasonably practicable steps to avoid accidents in the workplace.

This does not mean that you are required to completely eliminate all health and safety risks on your farm, but rather that you take all steps that are reasonably practical to ensure you and your staffs work in a safe environment. This means practicing sensible risk management and introducing controls that are proportionate to the risks.

Buildings health and safety in the farm

Because of the nature of farming and the potential hazards that a typical farm may present, the Department for Environment, Food and Rural Affairs has also worked in partnership with the HSE to develop guidance for all farmers.

You as a farmer should;               

• Be certain that all buildings are kept in good repair and that floors are not overloaded, especially in feed lofts
• Provide handrails on stairs and ramps where needed
• Make sure there are safety hoops or rest stages on long vertical fixed ladders
• Keep all workshops tidy
• Equip inspection pits with accessible escape routes and cover pits when not in use
• Provide adequate lighting and replace any old lights
• Ensure there is good drainage and non-slip flooring for wet areas

Confined spaces in the farm

The farming workplace can provide a number of confined spaces like fuel storage tanks, grain silos and slurry pits and so on. These can present numerous risks that include drowning, asphyxiation and toxic gases. Accidents in confined spaces often result in multiple loss of life. To avoid any risks, you as a farmer should;

• Complete any work from outside the space whenever possible
• Enter confined spaces only when absolutely necessary and then only with adequate ventilation and after having tested that the atmosphere is safe for entry
• Fully assess the risks and decide on what control measures are necessary before entering a confined space
• Plan for emergencies including arrangements for rescue
• Be sure that sumps, slurry tanks, reception pits and spaces under slatted floors are properly ventilated and tested before entering

Construction in the farm

Any new buildings that are constructed in the farm, or that undergo significant modifications, must be undertaken in accordance with the Construction which is the design and management Regulations taking account of the relevant standards. Your local authority will have building inspectors that can advise whether planning permission and building regulations may apply to your proposed building work in the farm. If you are constructing a steel-framed building, these have a higher risk of collapse during their building process. You will need to take special precautions for this work.

Farm building roofs

Most farm buildings have a fragile roof. They were designed to keep the weather out, and not to bear weight. Fragile roofs should never be walked across unless suitable means to do so are in place to prevent injury from a fall. Once you have determined that work needs to be done, you will have to plan and carry out a risk assessment before work can begin in the farm. Decide if you have the skills needed to do this work safely, then select and use suitable access equipment. Any staging equipment or scaffolding must meet correct specifications.