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IndustryArena Forum > CNC Electronics > Spindles / VFD > How low can I drop my rpms on my spindle?
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  1. #1
    Join Date
    Mar 2017
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    173

    How low can I drop my rpms on my spindle?

    Hi guys
    I have a 2.2kw water cooled spindle and my vfd is the askpower 131. I attach the manual of my vfd.
    I have been dropping it as low as 100hz which means 6000rpm. I would like to know if I can drop it lower without hurting the spindle. Say 50hz or even lower if possible?

  2. #2
    Join Date
    Mar 2017
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    173

    Re: How low can I drop my rpms on my spindle?

    Anyone has any info?

  3. #3
    Join Date
    Nov 2013
    Posts
    4282

    Re: How low can I drop my rpms on my spindle?

    Hi,
    yes you can drop it lower but you won't get any increase in torque.

    Many spindles are air cooled and because the fan the fan slows as the spindle running such spindles at low speed is to risk a bad overheat situation.
    Your spindle being water cooled is less prone to overheat, but if you notice it getting hot stop immediately.

    A 2.2kW spindle has a rated torque of:

    T= (24000 / 60)*2*PI /2200
    =1.14Nm

    So don't expect to drive a 10mm tool in steel, in fact without taking light cuts a 6mm tool will stall a 1.14Nm spindle.

    Craig

  4. #4
    Join Date
    Jan 2005
    Posts
    15362

    Re: How low can I drop my rpms on my spindle?

    Quote Originally Posted by jimskeet View Post
    Hi guys
    I have a 2.2kw water cooled spindle and my vfd is the askpower 131. I attach the manual of my vfd.
    I have been dropping it as low as 100hz which means 6000rpm. I would like to know if I can drop it lower without hurting the spindle. Say 50hz or even lower if possible?
    Only if the Spindle you have has a 3000 RPM rating which some do, it won't have any useful torque below 6,000 RPM and most don't go below 7,200=120Hz as they mostly cut at this speed, at 6,000 RPM they barely make it and have a high possibility of stalling, once you stall your spindle damage is quite possible
    Mactec54

  5. #5
    Join Date
    Mar 2017
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    173

    Re: How low can I drop my rpms on my spindle?

    I want to drive 3mm tool to take light cuts on stainless. Like 0.3mm stepdown passes.
    I have run it at 6000 rpm very often.

  6. #6
    Join Date
    Nov 2013
    Posts
    4282

    Re: How low can I drop my rpms on my spindle?

    Hi,
    you can run 24000 rpm asynchronuos spindles slowly but they are far from their optimum.

    I was so dissapointed that my 24000 rpm spindle could not be run slowly and that it has so little torque to render it almost
    useless in steel and stainless that I made a second spindle using a direct coupled 1.8kW AC servo, 3500rpm, 6.2Nm comt, 18Nm
    overload. Works a treat in steel and stainless.

    Craig

  7. #7
    Join Date
    Mar 2017
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    173

    Re: How low can I drop my rpms on my spindle?

    Thanks for the info

  8. #8
    Join Date
    Mar 2017
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    173

    Re: How low can I drop my rpms on my spindle?

    Hi guys.
    I am bringing back the topic.
    Is it safe to run 6 and 8 mm drills at 3000rpm or lower to drill wood with the 2.2kw chinese watercooled spindle? The drilling operation I need is one 8mm and one 6mm holes that are 35mm deep. I do them at 6000rpm now but I would like to do them with lower rpm if possible. Any thoughts?

  9. #9
    Join Date
    Dec 2003
    Posts
    24216

    Re: How low can I drop my rpms on my spindle?

    Running them lower than the recommended limit can result in a burn out of VFD and/or motor.
    The inductive reactance of the motor is so low at the lower frequencies, it has to be kept in the higher range otherwise the current/heat is destructive.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  10. #10
    Join Date
    Mar 2017
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    173

    Re: How low can I drop my rpms on my spindle?

    Thanks for the answer. The operation lasts a few seconds. You think it is enough to create a problem?

  11. #11
    Join Date
    Dec 2003
    Posts
    24216

    Re: How low can I drop my rpms on my spindle?

    Depends if you want to roll the dice!
    O/L can happen in milli -seconds!
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  12. #12
    Join Date
    Mar 2017
    Posts
    173

    Re: How low can I drop my rpms on my spindle?

    Got it.
    Thanks again

  13. #13
    Join Date
    Jan 2005
    Posts
    15362

    Re: How low can I drop my rpms on my spindle?

    Quote Originally Posted by jimskeet View Post
    Got it.
    Thanks again
    There are some of these spindle that can run at 3000RPM but they have a higher torque than the standard and there amp rating of 10.5a is higher for the 2.2Kw spindle, they have a longer body and rotor

    Just remember a drill requires more torque than milling so if you go to low and stall your motor then you will damage it and the drive, it may take it a few times before total failure

    Get quality drills and they will run ok with coolant at the 6000 RPM most likely your minimum speed below 6000RPM there is no useful torque with these motors and even at 6000 RPM most find 7200 RPM is around what most find as an ok running speed as far as torque goes
    Mactec54

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