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Thread: How to Increase RPM on PM-25MV (or similar G0704)

  1. #25
    *Registered User* CNCJoseph's Avatar
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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    Quote Originally Posted by rcheli View Post
    When I said 2:1 I meant 1:2 motor:spindle. But you understood what I meant. I suppose it would work if the pulses were exactly 180 degrees apart on the encoder on the motor.

    This is how I made my index sensor. The reason there are two sensors is one feeds the CNC control and the other feed a tach on my DRO that I had from before CNC.
    I also made that slot a lot bigger by the time I finished it.

    Attachment 405188
    Rcheli,

    That is a very nice clean setup. I have actually thought about a similar setup with a few extra parts for a DIY encoder. Do you mind sharing the part number on your slot type photo sensor? Thanks.



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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    CNCJoesph. Check out the VESC controller. I suspect with some bigger IGBTs you could drive it just fine. I have a few of the VESC controllers here I bought for my daughter's electric Jeep toy. It is tempting to use one of them to play.



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    Member arizonavideo's Avatar
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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    OK I have a simple answer for the RPM problem if you want to stick with the stock motor which should be fine for most people.

    Make a new front pulley. In order to get to lets say 5K or 6K it has to be smaller. The large bore prevents you from going vary small. Just make the new pulley taller. This allows for the hi speed pulley to have a OD of about 1.3" and you now have room to make it a three speed setup over the stock two speed.

    For the motor it needs to be raised up about 1.2" If you don't make a new pulley a spacer might work. If you make a new motor stand then you can make room for as large of a pulley as you might want so any RPM could be had.

    If you guys watched the 9000 RPM video I made I said I dont think you should run the thing that fast.

    You might get lucky on the balance of your spindle but with a bolt on pulley it will never be totally balanced. On the belt drives that I used to make for the IH mills I would mount the pulley to the flange and then mount the spindle in the bearing holder and then finish turning the groves on the pulley. I could hold .002" of runout that way and it still at 8000 RPM or so you still have vibration.

    youtube videos of the G0704 under the name arizonavideo99


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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    Quote Originally Posted by CNCJoseph View Post
    Rcheli,

    That is a very nice clean setup. I have actually thought about a similar setup with a few extra parts for a DIY encoder. Do you mind sharing the part number on your slot type photo sensor? Thanks.
    Sharp GP1A51HRJ00F form Mouser https://www.mouser.com/datasheet/2/3...EN-1140738.pdf

    Here is my wiring note.
    How to Increase RPM on PM-25MV (or similar G0704)-img_5136-jpg
    This is a picture of the setup as I am running it.

    How to Increase RPM on PM-25MV (or similar G0704)-img_5131-jpg



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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    Was still doing some putting around myself and was about to pull the trigger myself on a 3PH AC motor and get 220 outlets installed when I came across this thread on this site talking more about DMM servos. I know rcheli is using a 1.8kw servo with good results, but the post also mentioned .75kw ones that already max out at 5k rpm. Not to mention it's something like $400 vs $600 (give or take). Can anyone weigh in on this? The post mentions there should still be plenty of low end torque and hopefully high end torque for both steel and aluminum cutting. Just looking at the .75kw vs the 1.8kw it's rated for 2.4nm torque and 7.1nm max instant vs. 11.5nm and 28.7nm max instant. That's quite the difference, so does 2.4nm even compare on mills these size? What do the torque values on these 3PH AC motors look like? I wish we had torque numbers for the stock motors on these benchtop mills to compare to.

    One of the other appeals to this (besides money) is that it can run off either 110v or 220v. Correct me if I'm wrong, but if the .75kw motor is rated for 150v and I only apply 110v to the drive, wouldn't that take away from some of the torque/horsepower? And vice versa if I apply 220v to the drive it will A. step down the voltage to the max rated voltage of the motor(150v on the .75kw, and 200v on the 1.8kw) and make max power/torque available and B. it should use less current than on 110 because...that's how it works if I'm not mistaken. Another appeal is an included encoder (so rigid tapping should be pretty easy) and should, in theory, help combat motor bog since it knows exactly what RPM the motor should be going vs. what it's actually going at.

    So would a .75kw DMM servo on 110v seem viable for a G0704 sized machine, or is it a joke and I should continue with my 3PH AC search?



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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    Check with DMM tech support to confirm the speed you will get with 110v. My 1.8 can also run on 110 or 220 but on 110 it will only go to 1500 rpm.



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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    Quote Originally Posted by rcheli View Post
    Check with DMM tech support to confirm the speed you will get with 110v. My 1.8 can also run on 110 or 220 but on 110 it will only go to 1500 rpm.
    Interesting-I wouldn't have thought power input would cut the RPM. Maybe it cuts RPM to compromise and keep the HP/torque. I'll send them an email and find out for sure.

    There's a good chance I'll get 220 outlets anyway since that's a good excuse to buy a welder too, so if I had it on 220v do you have any idea how a .75kw would hold up? Not that I'd really expect you to know when you have the big boy version of the motor but I figure it can't hurt to ask.



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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    Not sure about how it would perform but in order to get to your original low-end goal of 7500 RPM would have to gear the motor a 1:1.5. That would mean about .67 HP at the spindle.



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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    rcheli, keep in mind that spinning 7500 RPM will also be running a smaller diameter cutter. The power requirements are not nearly the same as a 2.5" face mill or some other tool that struggles with the factory motor. I'm not saying it won't need more power, just don't get too focused on the drop.



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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    Quote Originally Posted by hackish View Post
    rcheli, keep in mind that spinning 7500 RPM will also be running a smaller diameter cutter. The power requirements are not nearly the same as a 2.5" face mill or some other tool that struggles with the factory motor. I'm not saying it won't need more power, just don't get too focused on the drop.
    You know, that's actually a great point. I could always have a 1:1 speed and high speed (1.5:1 or whatever) set that's swapable. Use 1:1 basically all the time so I can utilize rigid tapping and general use and swap to high speed and just do the math when I program if I want 7500 RPM with a 1.5:1 ratio for a 1/8" tool just tell my program to go 5000RPM and It will reach 7500 at the spindle. Now I just need a 4th axis to make all these custom pulleys...



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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    I was thinking of a solution with my acorn setup for rigid tapping. Put an encoder on the spindle for the Acorn, but run the servo in torque/speed mode. The acorn can then control the speed and the Z travel for rigid tapping while the servo controller manages the motor to produce and maintain the speed that the acorn is asking for. We know that there is no way to control the servo motor except with the encoder on its shaft, and any ratio changes or pulley slippage is going to mess things up for the motion controller. That make sense?



  12. #36
    *Registered User* CNCJoseph's Avatar
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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    Thanks so much to everyone for all the invaluable input up until this point.

    The exciting news is that I went ahead an pulled the trigger on a Leeson 1.5 hp motor this morning. I think it will work perfect for what I am trying to do. The only catch is that these motor are on back order for the next 6 weeks. One of the Leeson motor reps bent over backwards and checked every warehouse in the entire country for me. However, like everyone else who has the CNC bug, I've got plenty of other project to work on in the meantime.

    Out of all the other options I looked into, rcheli's suggestion to use DMM Technologies DYN4 1.8 kw servo as the spindle motor as he did on his Sieg X3 conversion project was my favorite. This option is pricey, but you get a lot of power. Also, even though the DMM Technologies servo has a built in spindle, you still need to build a separate encoder with one line per rev on the spindle. In my mind, if I'm going to do the work, I may as well just "upgrade" this to a complete spindle encoder solution and use a less expensive 3-phase motor / VFD.



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