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  1. #1

    Join Date
    Jun 2020

    Feed questions

    Hi all,

    I am a pretty new member with some experience in CNC with routers. We recently acquired a 3 axis milling machine. A Primero KM 450L.
    To give an idea of the specs:

    X axis 450mm
    Y axis 300mm
    Z axis 450mm
    Spindle nose to table max 580mm
    Spindle nose to table min 140mm

    Spintech 7.5 kW 8.000 rpm
    BT40 Servo Mitsubishi & Vector Drive Fuji
    Oil cooled

    Cutting feed 10m/min
    Rapid X,Y and Z @ 20m/min

    I think the rest are irrelevant.

    We are cutting and engraving polycarbonate, acetal, HDPE and aluiminium (6000 series). The tools we are using vary, we get JJ Tools (Korea), SARA, and Maykestag. So far the tools behave ok. Our main field is motorsports, we manufacture parts for racing motorbikes. We were outsourcing them so far, and it was decided that we have to get into the manufacturing to decrease lead times and have a bit more control on the production, at least in some of the parts/designs.
    Software-wise, we use Autodesk Inventor with CAM, and we have good results, both when using the adaptive clearance functions and the normal CAM cutting ones.

    Based in Europe, we are using the metric system, and although I have tried online for quite a while now to find some basic rules of thumb as to where we can start our cutting speeds (feed, cutting speed and rpm) , I have not been able to find something. Most threads or internet information, seems to favor routers because the rpms mentioned are sky high.

    I would like to kindly ask the community if there is a way to do that, of course depending on the number of flutes etc. But for example is there a rule of thumb for the feed per tooth so we work backwards? I have found that the specs that the tool manufacturers give is usually on the fastest side, so we are going lower than what they specify, but still when we are out of their spec range (for engraving they are talking about 24k rpm for example), then we go max rpm and slow feed. Just to be safe.

    Your help is much appreciated,
    Many thanks everybody, I kept reading since almost January to get information and it is a joy


  2. #2
    Gold Member
    Join Date
    Apr 2004

    Re: Feed questions

    The first thing you need to figure out is the "chip load per tooth" of the endmill you plan to use, for the material you want to cut. Here's one for metals that's metric: https://www.the-carbide-end-mill-sto...c.pdf?direct=1 There are other ones for plastics.

    Once you've got that, you can plug it into a feed/speed formula (like these: https://zero-divide.net/?shell_id=15...feeds-formulas ) to juggle other factors like feedrate, RPMs, and depth of cut; all these things vary depending on your machine, your tool, and what you're machining. As you've noticed, most of these charts or calculators tend to err on the high side, assuming you've got a fast, rigid, powerful and correspondingly expensive machine. If yours lacks in those respects, you'll need to back off on the recommended speeds. It's also important not to go with too conservative a chip load, since if it's too small you're not actually forming a chip, and you can melt the plastic or burn the wood by rubbing more than cutting. Here's a lot more info if you want to dig deeper into this topic: https://www.cnccookbook.com/feeds-speeds/
    Andrew Werby

  3. #3
    Join Date
    Jan 2018

    Re: Feed questions

    There's these examples for 3 flute

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