Feedrate and RPM for plywood 6mm compression bit


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Thread: Feedrate and RPM for plywood 6mm compression bit

  1. #1
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    Default Feedrate and RPM for plywood 6mm compression bit

    Hi,
    I'm using a 6mm diameter compression bit to mill a 10mm thick plywood sheet.

    I have a MM-1000 spindle with a Stepcraft machine.

    My settings are:
    21000 RPM
    40mm/sec feedrate
    1.3 pass depth

    For some reason the spindle lags and jumps a bit sometimes, as if it's running through a tough spot in the wood. That's how it "sounds" like, because it soudns like it's skipping a few spins, but the plywood
    doesn't have tough spots and I don't understand why it's not a smooth sound.

    Has anyone run into this issue?
    I've tried going 30mm/sec but that didn't really help.


    Thanks

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    Default Re: Feedrate and RPM for plywood 6mm compression bit

    1.3mm pass depth with a compression bit seems to be a pointless use of the tool as it will be acting as an upcut only. It also looks like an ambitious feed rate for a fairly tiny spindle-the fact that it comes as standard with a 1/8" collet is a clue that you can't expect too much from it.Have you tried a smaller bit,perhaps a straight 4mm,so the motor doesn't have to work as hard?



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    Default Re: Feedrate and RPM for plywood 6mm compression bit

    Hi,
    Thanks for the reply.

    I understand what you say about the compression bit pass depth, but I'm trying to achieve a relatively clean border edge. From my experience the upcut alone creates more splinters at the edge which is quite ugly...

    I can try to use my 1/8" compression bit for example, would that work better?
    I still need to keep the pass depth at 1/2 of the bit diameter, so I'm not sure how deep I can safely go with an 1/8" bit... any advice?

    Would you recommend:

    1/8" compression bit or upcut bit
    21000 RPM (or lower??)
    30mm/sec feedrate


    Thanks!



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    Default Re: Feedrate and RPM for plywood 6mm compression bit

    I still need to keep the pass depth at 1/2 of the bit diameter
    For what reason? You can easily cut 1/8" deep/pass with a 1/8" bit.

    The main limiting factor in how deep you can cut is your spindle power, and machine rigidity.

    For some reason the spindle lags and jumps a bit sometimes, as if it's running through a tough spot in the wood. That's how it "sounds" like, because it sounds like it's skipping a few spins
    Spindles don't "skip". Variable speed routers like that can slow and speed up as the cutting load changes, which may be what you are seeing. This would be more apparent during changes in direction, when the machine slows down, and speeds up.


    21,000 rpm is too high for what you are doing, but what a good rpm would be depends on how rigid your machine is. I would slowly reduce rpm, until you see the cut quality decline.

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: Feedrate and RPM for plywood 6mm compression bit

    I usually don't go too deep relative to the bit diameter because it already happened that the spindle couldn't handle it and was dragging really bad through the wood.
    I think my machine rigidity is very poor.

    How would you set it up in this case?



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    Default Re: Feedrate and RPM for plywood 6mm compression bit

    I agree that an upcut will create splinters and that is why I suggested a straight tool,by which I mean one with no twist.If you are running a compression tool at very shallow dop it is acting as an upcut and you are likely to experience splintering.A smaller diameter will reduce the work the spindle has to do and may allow a little more feed speed.I expect your machine will seem less flexible if it doesn't have to push quite as hard.Good luck.



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    Default Re: Feedrate and RPM for plywood 6mm compression bit

    Okay, thanks! I'll try that.



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    Default Re: Feedrate and RPM for plywood 6mm compression bit

    I tried going for the smaller bit diameter. It seemed to work much better. I'm not sure if it's perfect but going 4mm or less is definitely improving the process.

    Thanks.



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