Feeds and Speeds - Guide for beginners

SFM = surface feet per minute
I rarely use this parameter.

I also like this chart.

It’s important to remember that these charts are for industrial CNC routers that approach theoretically perfect rigidity and are equipped with large powerful spindles. While the 1F is really rigid for a machine in its class, starting out at a smaller chip load and working your way up is OK. Don’t burn up your tools using <.001” chip loads, but experimenting around the recommended values is always worth it. There are also various combinations that yield the same chipload, so trying different spindle speeds and feed rates for the same chipload can be valuable.

Cutting tool quality is another factor worth considering when selecting feeds and speeds. I’ve usually gotten what I’ve paid for with tools. Maybe reduce your chip load a little if you spent <$1 for a 1/4” solid carbide bit :joy:

If you think about it, the chips are what evacuate heat from the cut. If the chips are tiny, they have very little thermal mass and won’t move any heat away from the cut. This can cause burning in the extreme cases. That heat also makes the bit material more ductile and the cutting edges dull more quickly. BUT if you try to make huge chips for crazy long tool life, the surface finish will be really poor and/or you could stall your machine or spindle/router. It’s about finding the balance for your setup, workholding, finish requirements, etc… all the theory provides a good stating point, but there’s nothing like making chips to determine what size they should be for YOUR project.