The road to excellent, high-quality routing: simplified

When you start routing with a CNC router, at first you might think it’s easy, but quickly it will dawn on you routing might even be considered a kind of black art. Especially when trying to understand or master certain applications. However, do not be discouraged because in this blog you will soon learn to get the most out of routing, in a simplified understandable way.

The first thing to consider before you start routing is the choice of the bit. A bit can differ in various ways, depending on the type of flute, coating, purpose, spiral shape, etc. Knowing the difference between these bits is indispensable to optimally process your specific routing job. Here are a few key points to consider when choosing your bit for the job.

Multi-purpose versus material-specific bits

Most bit manufacturers offer either multi-purpose or material-specific bits.

Multi-purpose bits generally cut through most types of material and are, therefore, considered to be a safe bet. However, although they will give you a decent finish at all times, it might not be the best possible finish. Also, in terms of durability, these bits will hold a decent lifespan, yet not the longest possible.

Material-specific routing bits, on the other hand, can offer you the best possible finish and the longest bit-lifespan as they are dedicated to that particular type of material. These bits have specific coatings, resulting in a smoother and nicer finish, whilst offering an extended lifespan in comparison to the multi-purpose bits.

A common mistake with the multi-purpose bits is that operators tend to use these bits on a multitude of materials – for they are indeed called multi-purpose bits. However, it is better to keep the following rule of thumb in mind: if you use a multi-purpose bit on one type of material, make sure you dedicate this particular bit to that type of material only. Then each type of material wears down the bit in its specific way. So, if you use this multi-purpose bit in the same type of material, this will result in more gradual wear of the bit, which will, in return, result in the most optimal lifespan of your bit.

Upcut versus downcut bits

In general, bits have a spiral on them, which will rotate around the shaft towards the top. The type of spiral will then dictate whether the chips are transported towards the top (upcut spiral) or towards the bottom (downcut spiral) of the bit.

Most used spirals (bits) in the field are upcut spirals because they tend to assist in keeping a nice and clean surface as the debris is pushed towards the vacuum cleaner brush. However, if you need to route very small pieces you are far better off using a downcut bit. Otherwise, with the upcut bit, you’ll end up searching for the routed pieces in your vacuum cleaner’s bag. Moreover, the upward force, generated by the spiral of the bit will cause the small pieces to move around whilst routing. If you would use a downcut bit in this case, the routed pieces will be pushed downwards onto the router bed instead.

Therefore, the choice between upcut or downcut bits, with their exerted forces, are definitely something to take into account. Another example, if you notice that the top part of the routing path is frayed, it is better to exchange the upcut bit into a downcut bit, as the upward forces exerted on the surface of your material might be too large for the top layer of the material when routing with an upcut bit. Often signmakers will do the test by sticking a piece of vinyl on top of the hard material before routing. If the top vinyl is torn apart whilst routing this means the upward force is too large. A downcut bit would be more suited here.

Single flute versus multi-flute bits

Single flute and multi-flute are two other bit categories to take into account when routing. Choosing one or another has much to do with the so-called chip load, which applies when cutting. The chip size is related to the rotational speed of the bit and its feed rate (or cutting speed). Every bit contains a specified ‘chip load’ for a specific material. Chip load is basically the relation between the size of a cut material chip and the size of the flute and/or the number of flutes.

Generally speaking, between these two options, the single fluted bits are safer and easier to use. A single fluted bit will chop off a chip of a specific size as soon as it hits the material. By using a single fluted bit, set at a certain RPM (Revolutions Per Minute), you will be able to cut at a specific speed, dictated by the chip load.

So, when do you better opt for the multi-fluted bits? If you are cutting too slow with the single fluted bits, they will generate too small chips, which would result in your material being ploughed instead of cut. On the other hand, cutting too fast will generate too large chips and will wear your bit quickly or even break it. If you then replace the single-fluted bit with a multi-flute version, smaller chips will be generated at a similar speed as the single-flute version, enabling you to use higher cutting speeds. Consequently, your productivity will increase considerably.

Be aware that the multi-fluted bit has its restrictions, as well. When calculating the necessary speed for a certain chip load of material, a multi-fluted bit could dictate a cutting speed, which is so high your router can’t handle it, or too fast for the vacuum cleaner to clean. If this is the case, replacing the bit into a single-fluted one does the trick. Thanks to the larger extraction channel, a single fluted bit will have fewer issues getting rid of your chips, while the multi-fluted bits would struggle and get clogged up quickly. Also, with multi-fluted bits, it is more difficult to create the perfect edge geometry, since they are a lot smaller. And the better the edge geometry, the better the bit will cut, thus resulting in a better finish.

As with many things, it's a matter of trial and error to find out which bit works the best for your particular job.

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The higher the power, the quicker the cut, or so you might think…

A common mistake is to look at the power of the router motor to determine the router’s productivity. But if you want to achieve high cutting speeds, this doesn’t imply you need raw power (watts). What you do need, is Revolutions Per Minute (RPM). So the more your bit rotates, the more the cutting edge will strike your material and the quicker it will cut. However, there’s a ‘but’ here.

We already came to the conclusion that the higher the wattage on the router motor, the larger the routing bits you can use, resulting in more material being removed in one rotation, which will generate higher cutting speeds. Yet, consider this if you have a 1Kw router running at 40.000 RPM and a 3kW router, which is also running at 40.000 RPM. Basically, both routers are cutting at the same speed, when using the same bit. However, if you want to cut at a higher speed on the 3kW router, you’ll need to use a larger bit diameter. The drawback here is, that you are removing a lot more material, resulting in fewer details in your designs.

So remember, it’s all about RPM, not power.