Cutting A Thread (project 2)the Mechanic

Mill Machining, Milling Process, Horizontal & Vertical Milling Machines

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Definition

Milling is a process performed with a machine in which the cutters rotate to remove the material from the work piece present in the direction of the angle with the tool axis. With the help of the milling machines one can perform many operations and functions starting from small objects to large ones.

Milling machining is one of the very common manufacturing processes used in machinery shops and industries to manufacture high precision products and parts in different shapes and sizes.

Milling Machine

The milling machines are also known as the multi-tasking machines (MTMs) which are multi-purpose machines capable of milling and turning the materials as well. The milling machine has got the cutter installed up on it which helps in removing the material from the surface of the work piece. When the material gets cooled down then it is removed from the milling machine.

Milling Process

The milling machine involves the following processes or phases of cutting:

Milling Cutters

There are a lot of cutting tools used in the milling process. The milling cutters named end mills have special cutting surfaces on their end surfaces so that they can be placed onto the work piece by drilling. These also have extended cutting surfaces on each side for the purpose of peripheral milling. The milling cutters have small cutters at the end corners. The cutters are made from highly resistant materials that are durable and produce less friction.

Surface Finish

Any material put through the cutting area of the milling machine gets regular intervals. The side cutters have got regular ridges on them. The distance between the ridges depends on the feed rate, the diameter of the cutter and the quantity of cutting surfaces. These can be the significant variations in the height of the surfaces.

Gang Milling

This means that more than two milling cutters are involved in a setup like the horizontal milling. All the cutters perform a uniform operation or it may also be possible that the cutter may perform distinct operations. This is an important operation for producing duplicate parts.

Types of Milling Machines

The two main configurations of the milling machining operations are the types of milling machines. These are the vertical mill and the horizontal mill. They are further discussed below:

Vertical Milling Machines

The vertical mill has a vertically arranged spindle axis and rotate by staying at the same axis. The spindle can also be extended and performing functions such as drilling and cutting. Vertical mill has got two further categories as well: turret mill and bed mill.

The turret mill has got a table that moves perpendicularly and parallel to the spindle axis in order to cut the material. The spindle is, however, stationary. Two cutting methods can be performed with this by moving the knee and by lowering or raising the quill.

The other is the bed mill in which the table moves perpendicular to the axis of the spindle and the spindle moves parallel to its axis.

Horizontal Milling Machines

Cutting A Thread (project 2)the Mechanics

The horizontal mill is also the similar cutter but their cutters are placed on a horizontal arbor. A lot of horizontal mills have got rotary tables that help in milling in various angles. These tables are called the universal tables. Apart from this all the tools that are used in a vertical mill can also be used in the horizontal mill.

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Cutting A Thread (project 2)the Mechanical

General background and Pre-checks

• Determine which thread size you wish to cut
• Metric threads, M4, M5, M6, M8, M10 & M12 are commonly used.
• M4, for example, means the 'standard' M4 thread size: for a bolt, the outside of the thread would be 4mm in diameter, and the spacing between threads (the pitch) would be 0.70mm.
• There are 'non-standard' M4 thread forms, which will have different pitches, which are incompatible with standard M4. For example M4x0.5mm. This would be referred to as 'M4 fine', but some people would refer to any M4 pitch less than 0.70mm as M4 fine, so take care!
• Smaller than M4 you readily risk breaking taps in your workpiece (taps are harder than drill bits, so this might mean you've ruined your workpiece).
• There are alternatives threads to metric threads, such as UK imperial threads, the US has a different set of imperial threads, there are special Model Engineer threads, special Cycle threads. Pipe threads are common (though beware, the diameters of pipe threads refer to the internal diameters of the pipe, not the outside diameter of the thread) as are BA (British Association) threads.
• Find out the correct hole size to drill for the thread you wish to tap
• standard metric tapping drill sizes:
• M4 (x0.70mm pitch) - tapping drill 3.3mm
• M5 (x0.80mm pitch) - tapping drill 4.2mm
• M6 (x1.00mm pitch) - tapping drill 5.0mm
• M8 (x1.25mm pitch) - tapping drill 6.8mm
• M10 (x1.50mm pitch) - tapping drill 8.5mm
• M12 (x1.75mm pitch) - tapping drill 10.2mm

Step by step (Internal) Threaded Holes (Using a Tap)

1. Turn the handle of the wrench to wideren the jaws, fit the threading tap with with single groove to start.
2. Use a centre punch mark to centre the drill point.
3. Drill a hole smaller than the measure needed for the tap
4. Put some Rocol cutting compound on the end of the tap.
5. Holding the level and square to the material turn the tap wrench until the first cut into the material has been made.
6. Once a grip on the material has been made turn half a turn into the material and then a quarter turn back this will ensure that the tap doesn't get clogged with the offcuts of material and a better thread is created.
7. Keep turning until all the way through the material and most of the way through the thread, there should be no resistance once the cut has been made the full distance through the material when turning in or out using the tap wrench.
8. Once through the material using this tap repeat the process using the tap with 2 grooves and then finally again using the tap with no grooves.
9. Check the threading using the approparate sized bolt.

Step by step External Threads on Rods (Using a Die)

1. Fit the die with the sizing information on the die facing up and the top screw fitting into the slot, making sure all the screws are loose to allow the die to sit flush.
2. Tighten up the screw on the die holder to keep the die in place, ensure all the screws fit in the indences in the die.
3. Put some Rocol cutting greese on the end of the rod to be threaded,
4. Place the rod in a vice square and tighten, use a set square to ensure the rod is square in the vice.
5. Place the dice on top of the rod and turn to create the first cut.
6. Once a grip on the material has been made turn half a turn into the material and then a quarter turn back this will ensure that the die doesn't get clogged with the offcuts of material and a better thread is created.
7. Keep turning until the depth of thread is achieved, there should be no resistance once the cut has been made level and squre to the rod
8. Check the threading using the approparate sized nut.

Addition Thread Data

Data for other thread types is shown below:

The following sources of data are taken from the now discontinued site www.alanstepney.info :

• Data on various common UK imperial thread sizes
• Data on various common US imperial thread sizes

RLR20, 23 March 2016