How-To: Feed Rate Calculation

[Lee Roberts]

Today I received a question about feed rates regarding PCB’s on a DIY cnc router, so here we go.

In general when it comes to building a tool path; you will need to determine the correct feed rate. Different materials have different surface speed ratings for any given type of cutter.

As you can imagine the harder a material is, the slower we would set our speeds to. So, if we take the diameter of the cutter we would like to use and then also the surface speed of the material we would like to use, we can then calculate the correct RPM’s for our spindle.

Next we need to know the tooth load and also the number of teeth for the cutter, now we can determine the correct feed rate.

We can do this with the following calculations:

Spindle Speed = 3.82 * Material Surface Speed / Cutter Diameter
Feed Rate = Tooth Load * Number of Teeth * Spindle Speed

So using the above we could take a 6mm Cutter, a Surface Speed of 280 and this would give us a Spindle Speed of 178.3rpm. Now we can take our Tooth Load, times it by the Number of Teeth our Cutter has, and then times that by our Spindle Speed. This gives us a feed rate of 0.7, all units being in English of course!

Hope you found this useful and can use it to get that feed rate you have been after!

Lee