CC Feeds and Speeds Suggested Rates

Just trying to wrap my head around the feeds and speeds topic (again, new at this, so pardon the naivete) and how seriously I need to take this as I am learning my way around my machine. I definitely understand the basic concept and understand that it takes some complex math and calculations to properly set things up manually. I’ve reviewed a couple of the spreadsheet type applications that some folks have posted, but, honestly, still don’t quite get all the variables and still can’t bring myself to understand how to “program in” the various parameters to get to the basics: how fast to plunge, how fast to cut, how deep to cut, how far to step-over, RPM, etc.

So, to my question: Is there a problem with using the F&S settings that are suggested by CC when one sets up his/her toolpaths? They seem to be be based off of the material being selected, the size of the cutter, and the operation being performed, etc. I was thinking that the software was doing some sort of internal calculation and was providing appropriate parameters for F&S when the toolpath was created. Am I off base here, or should I be committing some extra brain cells to more thoroughly understanding how to set F&S manually?

Thanks.

The whole feeds and speeds thing is a little daunting, so there are basically two ways to approach this:

  • follow recipes, from CC or somewhere/someone else
    • default feeds and speeds in CC are OK(-ish), so that is usually a reasonable starting point, and in most cases that will work out ok.
    • the only significant issue with CC feeds and speeds is that they are (still, sigh…) tuned for the Nomad, and specifically the Nomad’s RPM range. The Shapeoko has a very different RPM range (10-30k) and if you don’t understand yet the relationship between RPM, feedrate, and endmill type, your feeds and speeds can be way off. Look out for any case where CC recommends a sub-10k RPM.
    • sooner or later, you will need to adapt a predefined feeds and speeds recommendation to your specific case, and that’s when it helps to understand at least one simple formula:
      • chipload = feedrate / (nb_flutes x RPM)
  • follow guidelines to select individual cutting parameters as a function of [many things], and use calculators to make sure they are consistent with each other.
    • I have attempted to provide such guidelines here, it may still look a tad complicated, but in the end there are not that many parameters that you need to play with: nb of flutes, endmill diameter, target chipload, RPM, WOC and DOC.
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The stock feeds and speeds are extremely slow. You can do it without math, just seeing and hearing how the machine is performing is enough. If your chips are dust, your moving too slow and spindle speed to high. Something closer to pencil shavings is your goal. If you start skipping belt slow feed rates down/ increase spindle speed. Do some reading in the forum on other ppl s projects and try their settings, you’d be amazed how much faster things can be made

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And this, right here, is examplifying that you can either try to figure out the math, or just proceed to experiment and use your eyes and ears, both can be equally successful !

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Some rules of thumb:
If you are cutting wood, it’s probably better to run at a higher rpm than too low, although the typical routers only go down to 10k-12k rpm at the lowest setting. That is easy enough to adjust on the fly however. I usually try to run at a the lowest rpm possible, just to keep the noise down.

Also pay attention to the number of flutes on your cutter. A 2-flute cutter can be run at twice the feed of a single-flute cutter, for example. Smaller diameter cutters typically should be run at higher speeds, but lower feeds. Set your stepover to be 50% typically. Again, this is for cutting wood.

Also keep in mind that slotting is much tougher than pocketing because the cutter is basically doing a 100% stepover when cutting a slot, and chips may get clogged up in the slot. So you may need to use a smaller depth of cut or slower feed when cutting a slot.

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