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KBIC DC controller/chopsaw motor question

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  • KBIC DC controller/chopsaw motor question

    Is it possible to use a KBIC DC speed controller to slow down your typical wood munching miter saw motor? I'm guessing that since they have brushes, they're similar to a shunt-wound DC motor and as such might be speed controlled if wired correctly with a KBIC?

    Not looking to slow it down to a crawl but maybe 1/2 speed for cutting aluminum with a carbide blade. Got the miter saw, got the KBIC and am curious. Yes I'll admit to being electrically naive...stupid idea?
    Milton

    "Accuracy is the sum total of your compensating mistakes."

    "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

  • #2
    It should be possible, but I have never tried it, the saw has a Universal motor so it it will run on the DC output of the KIBC as long as the current rating of the motor is suitable.
    Being a series motor it is bad on RPM control under load without some kind of feedback, and basically operates in a runaway condition due to field weakening.
    I have used the SuperPID which is the way to go if you need precise speed of a tool with a universal motor.
    http://www.vhipe.com/product-private/SuperPID.htm
    BTW, there was one make of treadmill that used a Universal motor and a DC controller, but used a simple form of tach for feedback.
    Max.
    Last edited by MaxHeadRoom; 03-13-2012, 11:43 AM.

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    • #3
      Thanks Max, when you say runaway does that mean the speed cycling up & down uncontrollably?

      The exact speed isn't important, I'm just trying to slow it down to get a better finish and make the process less frantic.
      Milton

      "Accuracy is the sum total of your compensating mistakes."

      "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

      Comment


      • #4
        A series motor is only slowed down by friction windage etc, the field current gets progressively weaker with rpm, this is why/how universal motors achieve the 20,000 some odd rpm they are capable of.
        If you slow it down to something like 5krpm It should be OK on light cuts otherwise the rpm will vary quite a bit at that rpm without some form of feedback to correct it.
        Max.

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        • #5
          Sounds like it may be worth a try, thanks. If the deal I'm working on comes through, I may be chopping off a lot of 1 1/4" sq. aluminum bar.

          I'm thinking that if I go down to a smaller dia. blade & reduce the motor speed, I should be able to get the +/-.010" length spec. that's called for and a reasonable finish without having to mill the ends. I can almost do that now but blade flex and resonant vibes (?) makes the cut inconsistent. It'd be nice to have a cold saw but that's out of my budget for this year.
          Milton

          "Accuracy is the sum total of your compensating mistakes."

          "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

          Comment


          • #6
            The KB motor controller features built in speed control (back EMF sensing) that improves speed regulation for series wound motors. You will have to tweak the settings on the KBC drive but in the end your saw should run better under the drive at say half-speed than uncontrolled at full speed - if the drive is selected to suit the motor ratings, set up correctly, and the current, back EMF, and other trim pots are adjusted to optimize perfromance.

            Which KB drive do you have? There's about a dozen.

            http://www.kbelectronics.com/Variabl...es_Chassis.htm

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            • #7
              Thanks for the input Forrest. I have KBIC-120's. They're a great piece of engineering and can't be beat for the money. (Thanks again Max for leading me to them a while ago.)

              I need to ck. the motor's data plate and see what its rating is before hacking into it. May be too much for a -120 but I doubt it.
              Milton

              "Accuracy is the sum total of your compensating mistakes."

              "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

              Comment


              • #8
                I would tend to use a slightly higher value of current limit resistor, this would avoid over taxing the drive if motor current were to go too high, you could always drop the value to suit.
                This is what I have done in the past.
                Max.

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                • #9
                  I have done 60mm bar on mine without slowing it down. Get a big plastic bag you can put the whole miter saw in. Put the miter saw in the bag set up the stock (Use clamps) and bring the bag over the top to seal it up. I do hit the blade with WD40 before cutting. This keeps the chips confined to places other than down your shirt.

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                  • #10
                    I have cut 11/2" aluminum bar on my table saw with a carbide blade with good results. I used a blade stabilizer to reduce flex. I used a sled on the saw and clamped the bar to the sled so I could concentrate on feeding very slow, also a little shot of WD40 helps. There are carbide blades made for cutting non ferrous metals that have a negative rake to reduce grabbing. Just a suggestion.

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                    • #11
                      Good idea on confining the chips in a bag. I'll have to remember that one.

                      I've used mine to cut a 2"x4"x72" stick down to manageable chunks and it made short work of it. The blade was flexing & vibrating though and left a rough finish and was too inaccurate for use on this project. The blade I have now is a cheap 10" 80T carbide made for cutting wood but I'm looking around for a deal on a made for aluminum blade in a smaller size to reduce the SFM and try the speed control if the smaller blade doesn't work well enough.
                      Milton

                      "Accuracy is the sum total of your compensating mistakes."

                      "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

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                      • #12
                        Cut thru the vise

                        One thing that will greatly improve accuracy and finish and cut down on vibration would be holding onto both sides of the cut .This works well for me

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