Milling

David A Clark

• Éditeur: Crowood
• Année: 2014
• ISBN:
  9781847977755
• Sujet: Technik & Maschinenbau
• Sous-sujet: Technische & produzierende Gewerbe

Milling is one of the principal and most versatile machining processes for sizing parts in the workshop. Whether a professional engineer looking for advice, or an amateur looking to install your first milling machine, this book will show you how to make full use of your milling machine safely and effectively, and enhance your milling skills. Focusing on the commonly used vertical mill and vertical turret mill, and with practical advice and diagrams throughout, the book includes: a guide to buying, installing and using a small milling machine and accessories; basic cutting tool principles and more advanced milling methods, including drilling, tapping and reaming; and instruction on a variety of techniques ranging from work holding in the vice to using a rotary table. Aimed at anyone with a workshop, and particularly home metalworkers, engineers and professionals, and fully illustrated with 167 colour illustrations and 45 diagrams.

1 The Milling Machine

The machines we will be discussing in this book are the vertical milling machine and the vertical turret milling machine. The principles of milling are also applicable to the horizontal milling machine, and some horizontal milling machines can be fitted with a vertical head (when they are known as universal mills). Usually these are fixed heads and do not have a moving quill, however, so the only way to adjust the depth of cut is to raise and lower the mill’s table. Also available are slotting heads which bolt on in place of the vertical head, and the tool moves up and down rather than rotating.

The vertical milling machine is basically the same as a turret milling machine, but the turret milling machine is much more versatile. While both types of milling machine have their spindles in the vertical plane, the turret milling machine spindle can usually be tilted to the left or right and sometimes forwards and backwards. The plain vertical milling machine can usually only be tipped to the left and the right, often by tilting the whole vertical column that the head is mounted on.

A typical example of a turret milling machine is the Bridgeport style mill. This is quite a large machine, but many are finding their way into the home workshop. These mills are a standard item in many industrial workshops and are often available at a reasonable price. They do however require a specialist machinery transport company to move them as they are very heavy and are not really suitable for the amateur engineer to move by themselves.

Fig. 1.1 A typical bench mounting vertical milling machine as used in home workshops is the Warco WM 14 milling machine shown here. You can buy purpose-designed cabinet stands for most of the Warco range.

Fig. 1.2 The Warco WM 16 milling machine can also be supplied for bench mounting.

A typical vertical milling machine will be much smaller than the Bridgeport milling machine and can often be moved by two people, possibly assisted by an engine crane if it is a larger mill. It is usually possible to split the milling machine into two parts: the base unit complete with the machine’s table, and the column with the head and motor assembly combined. When you have lifted the base onto the bench or machine stand, you can then add the column and head.

Also available are much smaller turret mills than the Bridgeport, often called VMCs (vertical machining centres). On a turret milling machine the head can usually be twisted to the right and left and rotated around the column, but it cannot usually be tilted forwards and backwards.

Fig. 1.3 A Bridgeport milling machine can often be found in commercial factories, but more and more are finding their way into home workshops. They usually have a self-contained X axis power feed gearbox for moving the table under power feed.

Fig. 1.4. This Warco WM 16 milling machine, seen here on its purpose-made stand, is often found in the home workshop.

CHOOSING A MILL

Size

The first thing to decide is: what is the largest piece of work you will be milling on the machine, and what is the largest diameter you will want to hold in the dividing head.

It may be that the longest and widest item you will want to hold is a pair of locomotive mainframes. Perhaps the largest diameter is a traction engine rear wheel for drilling for the spokes and strakes and so on. The locomotive frames can be moved along the table so the table length and movement is not too critical. They can also be rotated 180 degrees to access the far side of the frame plates.

Fig. 1.5. A small turret milling machine will be found to be very useful in the small workshop. This example by Warco is typical of this type of machine. It is quite easy to fit a digital readout, a power feed attachment and a machine light to improve on the machine’s facilities.

A Bridgeport milling machine will usually have an X axis travel of 26in (660mm) and a Y axis travel of 12in (300mm) although I think this may vary slightly on some models. This will be sufficient for all but the largest models.

A typical medium-size, hobby-type milling machine will have an X axis travel of about 19in (485mm) and a Y axis travel of 7in (175mm). A small milling machine will have an X axis travel of about 13in (330mm) and a Y axis travel of 5.5in (145mm). These dimensions will vary with different manufacturers and should be considered a starting point only.

When mounted in the dividing head, the traction engine wheel can be almost twice the diameter of the Y axis movement, as the wheel rim can be rotated so that every part of the wheel can be beneath the centre of the milling machine spindle.

You will also be able to do larger work on a turret milling machine than on the vertical milling machine, as often the milling head can be moved in and out on the machine’s ram. (The ram is a large dovetailed slide on the top of the milling machine’s column that allows the milling machine’s head to move in and out and often to rotate.) In this case, you leave the work in the same position on the table and re-datum the work after moving the head on the ram. Often, the ram can pivot to the left and to the right to access all areas of the workpiece. If you are machining a large traction engine wheel rim on a turret milling machine where the head can swivel to the side, you can place the wheel on the table so that the table is in the centre and completely surrounded by the wheel.

Speed

The speeds required for milling will depend on the work you are doing, but unless you are doing very fine work such as engraving, a maximum speed of about 2,000rpm will be more than sufficient. A lot of the modern small mills will have an electronic speed control, sometimes combined with a high/ low gearbox. A Bridgeport milling machine will often have a two-speed motor as well as bac...