CNC Routers

Machining of wood materials, e.g. softwood, hardwood and sheet materials, aluminium, as well as plastics is possible with the CNC router.

This depends on the CNC router cutter used. For a clean top edge, we recommend CNC spiral flute cutters VHM with left-hand twist. The pressure on the material produces absolutely tear-free cutting edges. For the bottom side, a router with right-hand twist is used. If both cutting edges are to be machined in one process, so-called compression routers or dual-cut routers can be used, which have an opposite twist in different areas of the cutting edges. The left-hand twist at the end of the shaft ensures a tear-free top side, while the right-hand twist at the tip of the router ensures a tear-free bottom side.

For example, with whirling, the offset cut often results in unclean edges, which then have to be machined either manually or by a further CNC work step. Rough milling cutters also do not leave a high surface quality. Here, too, reworking is necessary, either manually or with a final finishing pass. In most CAM programs, it is possible to perform a final finishing pass, which is usually performed over the entire thickness of the material. Here the material is delivered to the area of the uniform cut edge.

One of the main factors for a successful routing result is the interaction of feed and speed. If the tool rotates too fast compared to the feed rate, no real chip is removed and the tool rubs more against the workpiece and generates dust. With wood, this leads to burns on the material and the router bit also wears out very quickly. With plastics and aluminium, this can quickly cause major problems.

• Plastic: gets too hot and melts instead of being cut.
• Aluminium: it can cause the aluminium to weld itself to the router bit, destroying both the workpiece and the router bit.

If, on the contrary, the speed is too low, this means too high cutting forces for the router bit, which often leads either to breakage of the router bit or to step losses at the stepper motors. This then leads to incorrectly converted routing paths and a destroyed workpiece.

In principle, there are also special tools designed for different materials and cutting types. These differ both in the material (HSS, carbide, etc.) and in the cutting geometries.

Roughing cutters, for example, have a rather aggressive cutting angle in order to remove a lot of material quickly without attaching great importance to the quality of the cut.

Finishing cutters remove little material and leave a clean cutting edge. Accordingly, flatter cutting angles are used here.

Routers with carbide cutting edges are suitable for wood and aluminium. These are either soldered to a steel shank (classic end mills for routers) or consist entirely of a carbide mixture. The number of cutting edges also plays a role in the tool life and the milling result. For aluminium, for example, single-edged cutters are often used to give the machine more time and to be able to remove the cut chips cleanly.

The most important key figures in routing are: Feed rate, speed and infeed

When routing pockets with many parallel toolpaths, a transverse infeed of <50% is often used. This means that each milling path overlaps only half of the previous path. The additional milling time required can then be compensated by a higher feed rate. The decision "climb milling or up-cut milling" can also have a decisive influence on the milling result. The correct cutting speed cannot be answered in a blanket manner. The best results are achieved when the CNC router is used to carry out some test routing in scrap stock.

If possible, it should be plunged outside the contours to be routed in order to then approach the contour to be routed from the side. In addition, a final finishing pass often leads to a cleaner, better result, as only a little material is removed and the router is also only loaded with 10-20% cross feed. When routing very delicate details (e.g. 0.5 mm cutter), patience is a virtue. Even if router and machine would manage higher feeds and speeds without any problems, with wood materials more defensive cutting values often lead to less tear-out on intricate routed parts.

When machining manually, e.g. at the router table with a router, only up-cut routing is permitted. When routing in the same direction, the material is drawn towards the cutter, which entails some safety risks and dangers. When machining on the CNC, the situation is different. The overall rigidity and the backlash of the machine determine whether down cutting is possible or useful.

If the machine allows it, however, down cuttingis preferred in the CNC area, as it has a number of advantages:

• Longer routing cutter service life
• Lower cutting forces
• Chip ejection behind the router and thus less "multiple machining" of chips
• Better surface quality