Nomad 3 and RPM setiings

[jcspball13 (Jason Cox)]

Being very new to CNC, I am wondering how the RPM setting effect the parts I am making

I am just working with aluminum right now, and have experimented with 16k-20k, but have not been able to figure out the difference

Can anyone point me in the right direction, such as rpm for certain flutes, etc. Any info would be great!

[Julien]

Long answer here. It’s in the “Shapeoko” ebook but that part applies to the Nomad (or any other desktop CNC) too

Shorter answer: chip thickness equals feedrate divided by (RPM x nb of flutes), so modifying the RPM while keeping other parameters unchanged will modify the chip thickness, so at some point it will impact the quality of your cut: too small and you will start rubbing, too large and you will exceed the maximum torque of the spindle. Other factors to be considered:

• cutting forces decrease with RPM increasing, so it’s often beneficial to max out RPM
• but some materials (metals, mostly) have a narrow “surface speed” (SFM, Surface Feet per Min) of the endmill that they tolerate, and surface speed is directly linked to RPM (and cutter diameter), so in those cases max RPM may not be the right choice.