Three, four or five axes?

When buying a machine, sooner or later it comes into question how many axes are necessary with main spindles.

The slogans "3-D processing" and "5-axis“ are hugely popular in advertisement. But are 5 axes really this necessary and do they come with all benefits? In fact: even with a 3-axis machine, the respective clamping devices and the according software one is able to produce many 3D-moulds, even a sphere, in two clampings. Most of the 5-axis machines cannot mill any spheres in a clamping either, as the processing from below and the process height are limited.

Benefits of 5-axis machines:

• Each point within the processing range can be approached in each desired angle. So it's possible to apply end mills with each desired shape perpendicular to the workpiece surface. Even more important for most of the users is the positioning of drills and saw blades in each desired angle.
• Unlike 10 years ago machines with 5-axis today are relatively cost-effective, the price difference to the 4-axis machine amounts to less than 10% with cheaper models. But those 10% may account for more than ten thousand euros.

Disadvantages of 5-axis machines:

• If only vertically milling is mostly happening anyhow, one should reconsider buying a 5-axis machine. The spindle only has two additional pivoting joints which tend to give at higher cutting force which may at its worst cause vibrations and/or inaccuracies.

Some manufacturers thus have developed systems which block the pivoting axis if vertical spindles are used. However one simple, vertical spindle is always construction-dependently stiffer than a 5-axis spindle.

• Because of the large freedom of movement the suction hoods of 5-axis spindles have to be arranged in a significantly larger distance from the spindle than with 3-or 4-axis spindles. This means a possiblly worse extraction and the necessity of applying an extraction with higher flow rate, which in return leads to more costs.

If one can already guess that the workpiece processing is not necessary on arbitrary angles and if one wants to execute a saw cut once in a while, one will go better with a 3-axis or 4-acis machine plus unit. The costs for the purchase but also the follow-up costs are lower and the operating quality is dependent on fewer factors.

But it's also necessary to consider that purchasing many units may eventually lead to procurement costs of a 4-axis machine to be the same or even higher than of a 5-axis.

Pure 3-axis machines are rarely to be found nowadays. They are rather mostly drilling machines with additional milling spindles. Here tools can be clamped in a mere vertical position.

The usage of angular units is also possible with 3-axis machines. An additional fixation, the torque support, facilitates milling of lock cases on doors.

But if an diagonal saw cut or e.g. a horizontal drilling on the cabinet side for a roof slope needs to be done, 3 axis are more than sufficient.

The fourth (C-axis) facilitates the controlled positioning of the torque support and thus the use of angular units in each desired rotation angle. The „inter polishing“ 4 axis which can sometimes be found in ad texts sometimes - meaning an axis pivoting during processing - is not important in practice, except when using an edgebanding unit.

... or 4 1/2 axis afterall?

An utterly popular alternative to the 5-axis machine from 10-15 years ago are units which facilitate a 5th axis on a 4-axis machine.

As the technology is associated to high costs und today 5-axis machines are on the market in the lower price segment, the market share of such units has decreased drastically in the last couple of years. Some manufacturers have taken this unit out of the program and have solely focused on the further development of 5-axis spindles.

Machines with such technology only have 4 driven axis but have an additional interface in command on which the drive of the C-axis can be switched over. The corresponding units have the same interface in command over which the tool can be panned in the unit. In case of pivoting the unit, the C-axis is applied as in any other 4-axis machine. In case the tool is to be pivoted in the unit, the drive switches the C-axis on over to the additional interface and pivots the tool.

A special form is the Flex 5 Axis technology developed by Weeke and Benz. Here the machine has over 5 driven axis in command, which don't position the spindles but the axis of an according unit. In theory a "real" 5-axis operation were possible with this unit but such has never been developed in software-form.