The vertical gantry is a type of construction used in machine tools that run on computer numerical control. This type of structure can be found in CNC milling machines and machining centres.
The vertical gantry in machining centres
The vertical gantry in machining centres is designed for machining large workpieces for heavy industry. That is why this type of machinery is commonly used to manufacture parts for the aeronautical, aerospace and automotive industries, which need to machine very large, complex parts with specific structures and components.
In a vertical gantry machining centre, the machine's spindle axis is perpendicular to the worktable. These machines can also be programmed in different ways and even adapted to machine several workpieces. Machines built with this structure offer a wide range of axis configurations, which vary according to the machining requirements.
In terms of structure, these machining centres have two columns, a cross-rail and sliding saddles. They are available with a fixed cross-rail, a moving cross-rail or travelling columns; it all depends on the type of gantry. For example, there are machining centres in which the upper cross-rail is fixed while the worktable moves. In others, the cross-rail moves up and down and the table moves forwards and backwards.
CNC vertical gantry milling machines
Milling machines were the first machine tools to be fitted with a computer so that processes could be carried out automatically. These machines run on computer numerical control, which means that the machine's computer controls the machining in every process. It is the computer that sets the cutting speed, depth of cut, feed rate and so on.
To machine large workpieces, milling machines also evolved and adopted the vertical gantry. That is why, together with machining centres, gantry milling machines are among the most widely used machines for producing workpieces, spare parts and components for heavy industry.
These milling machines have a frame (the gantry) and a long horizontal bed. The machine can work the surface of the workpiece with several milling cutters at the same time; remember that the milling cutter is the most important cutting tool on any milling machine and has multiple rotating cutting edges that remove chips when they come into contact with the surface of the workpiece. This is why machining accuracy and production efficiency are high on vertical gantry milling machines.
A vertical gantry milling machine includes not only CNC but also other mechanical, hydraulic, electrical and numerical systems. As a result, it can machine planes, surfaces and holes using a variety of processes such as milling, boring, drilling and tapping. The milling machine performs all these operations in a single set-up, so the operator does not need to reposition the workpiece: the machine itself can rotate and position it as required by the previously programmed machining sequence.
The main features of these machines include:
- Numerical control for centralised control of the machine.
- Servo drive systems.
- Rack-and-pinion drive systems and roller guides.
- Rigidity.
- High efficiency.
- Simple structure.
- Requires minimal human intervention.
If the gantry moves, the machine can be a fixed-table moving-gantry type or a moving bridge-type gantry. Bridge-type gantry milling machines have a small footprint and a high capacity for heavy loads. To give you an idea of the size of these machines, the gantry can travel up to 20 metres.
Machining centre or gantry milling machine?
Now that you know the vertical gantry is found in both machining centres and milling machines, you may be wondering what the difference is between the two, since both can machine large workpieces. A machining centre has a tool magazine and changes tools automatically; on a gantry milling machine, however, tools have to be changed manually.
This does not mean that milling machines offer lower performance than machining centres. A milling machine, for example, can perform different machining functions and use several milling cutters simultaneously to shape the workpiece. The production capacity of both machines has made them indispensable for machining large workpieces.