Why your Router Table should be Rigid and Heavy
Unicam makes its Router Table rigid and heavy, but why spend money on solid Router Table? It all depends on the speed and the quality of cut that you want from your Router Table. If you get a light Router Table, then it will vibrate, and you will only be able to cut at a low feed rate or you will break cutters or have rough cutting surfaces. A heavy solid table on the other hand will vibrate less, and this will allow you to run at a higher feed-rate.
What makes the Router Table Vibrate?
If you look at most of the European Router Tables that are imported into South Africa, they have Cast Iron or Welded frames with Large Bent Sheet Steel components as part of their frames. Why do they use these solid Router Tables?
When you look at what is happening when a Router is cutting, the spindle is turning at between 10 000 and 40 000 Revs per Minute. The spindle has a cutter with between 1 and 4 Flutes. Each time one of the cutting faces bites into the material that you are cutting, a shock wave is produced. This shock wave causes vibration which affects the quality of the Cut.
Let’s look at a scenario where you are cutting aluminium with a single flute cutter at 16 000 RPM, with a feed speed of 5 Meters a Minute.
Calculating the frequency and distance of induced vibration
16000 RPM / 60 Sec x 1 Flute = 266 impacts per second
5000 mm / 60 Sec = 83 mm per second
83 mm / 266 impacts = 0.31 mm
This will result in a surface that has a repetitive pattern every 0.31 mm, or to us, it will have a roughness. For most applications, you would think this is acceptable, but the frame also distorts from this impact, and it may not be at the primary frequency, it may be at one of the harmonics that suit the frame’s resonant frequencies.
Let’s assume that the above cutting is happening on a machine that can distort at a natural frequency at 88 Hz. This would mean that the third harmonic of the cutting frequency would resonate and give you a cut that has a 0.93 mm-wave in it. If the distortion of the frame were 0.5 mm, then the wave would be 0.93 mm long with an amplitude of 0.5 mm.
This would result in having to clean up the edges of your cuts by hand after machine.
So how can we improve the cut quality?
- More Rigid and Solid machines to reduce machine flex.
- Heavier base to lower the natural frequency of the base.
- Reducing Backlash on the drive system.
- Use a cutter with more flutes.
- Use a cutter with better cutting geometry.
- Better material fixing.
- Faster spindle speed.
- Slower feed speed.
- Using a more ridged cutter.
Other resources on this subject
Although this subject has major implications for all serious users of CNC routers, relevant information on the internet is misleading and conflicting. This is partly because the internet gets most of its information from unqualified people on forums, so when looking for information, try to find serious websites that are trying to help their customers get better finishes on their own machines. Another reason why information is often conflicting is because the environment that is being discussed is different. For example, chatter on a milling machine at 50 Hz is a completely different situation to chatter on a router at 20 000 Hz.