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  1. #1
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    Speeds of Cut

    Did I figure this out or did I overlook something? Different materials have different SFM because of how much heat they generate? Basically the tougher the material, the more heat, the slower you need to go? Is this correct? Is there more to it than this?

  2. #2
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    Re: Speeds of Cut

    It's the most basic, but heat is usually the most significant factor in SFM. Generally best to consult the manufacturers recommendations though, as different tools may want different speeds for the same material (HSS tooling nearly always should be run slower than carbide, but coatings and geometries come into play as well.)

  3. #3
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    Re: Speeds of Cut

    Merci Beaucoup. Interesting that aluminium is always listed with such high SFM given that it's pretty gummy.

  4. #4
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    Re: Speeds of Cut

    Aluminum you generally need to use coolant with because of that (flood, mist or MQL work. Or standing over it squirting it with WD40 if you have to.) It makes big chips and can be sticky, so you need something to lubricate it and clear it out.

  5. #5
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    Re: Speeds of Cut

    There's many factors to SFM, Have you heard the old saying? "You can't cut, what you can't hold" That saying is very true. SFM recommendations may work on a rigid machine with 1000psi through spindle coolant at 1200sfm and 200ipm feed but use that same tool on an older machine and you have to cut everything in half plus add a peck cycle. There's many variables..

  6. #6
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    Re: Speeds of Cut

    Spent some more time on this... yep, lots of factors for SFM, and the worst part is that most places you look have different recommended values!

    Another question.

    So I was playing around with a feeds and speeds calculator yesterday (GWizard) for a few hours and I was taking it as it came, but I had a think and something didn't make sense to me.

    I kept width of cut constant and was varying only the depth of cut. Why was the RPM and federate changing?

    To calculate RPM you just (Cutting speeds x 12)/(Pi x Diameter), so RPM shouldn't change no matter what depth no?

    The feed rate was obviously changing because the RPM was changing because chip load was locked in as constant also. But I don't understand why the RPM was changing with depth of cut?

  7. #7
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    Re: Speeds of Cut

    Beyond certain DOC or WOC (or combo of the two,) most manufacturers recommend reducing both the SFM and the chip load.

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