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Cooling off a hot treadmill motor.

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  • Cooling off a hot treadmill motor.

    I’m getting a teeny bit closer on my little CNC mill/lathe project and after test running the treadmill motor driven spindle wide open for a while to check the bearing preload, I found that the motor was heating up considerably since it had no cooling fan. I thought about mounting a fan blade on the rear shaft but figured it wouldn’t be enough at lower speeds. I had previously stripped down an old PC power supply to get its power socket for the motor hookup and thought hey, here’s a perfect little cooling fan motor as well!

    I whipped up an aluminum bracket to mount the fan on the rear of the motor and in tests it easily kept the motor nice & cool. It’s a 12V motor and runs great with an old 12v 150 mah wall wart wired into the system relay.

    I noticed that a lot of the air was wasted so I decided to make a duct to force all the air through the motor. I made v1.0 from stiff cardboard using a shareware cone generator program that outputs a .dxf. After playing CAD “paper dolls” and cutting out various templates, I wasn’t satisfied with the results and decided to try the old heat-shrink-the-2-liter-soda-bottle trick I used many times to make custom engine cowlings and canopies back in my model aircraft days. The P.E.T. plastic (polyethylene terephthalate) shrinks about 25-30% at approx. 400 deg f. and is amazingly tough stuff after shrinking.

    I made a wood plug that duplicated the shape of the fan housing and the motor O.D. I turned the round end in the lathe, shaped the transition from round to square with the mill, a plane and coarse sandpaper. I then glued on a pair of blocks to make bumps to clear the brush boxes and then shrunk a bottle tightly around it. I slit it down one side to remove it from the plug and then installed it with a tyrap, a piece of aluminum 200 mph tape and a strip of filament tape. It fits perfectly! I’ll eventually put a screen on the inlet side to keep stray chips out of the works but am happy with how it came out for now.







    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
    Wow nice trick, I will have to remember that one.
    Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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    • #3
      That is excellent.

      It is now a bookmark!!!!!

      Very good

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      • #4
        Now there is something I didn't know that is worth remembering.
        A big THANKYOU for that tidbit.
        ...lew...

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        • #5
          Polyethylene terephthalate has a recycle code of 1 (picks up nearly empty jar of peanut butter -- much heaver than soda bottle) Hmmmmm What shall I make????

          Thank you very much DICKEYBIRD, I too am going to try this!

          If you could seal up the end and put vacuum on the other end, might be able to do more complex shapes????
          Last edited by fredf; 04-17-2011, 01:14 AM.

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          • #6
            Excellent job. PET-G is one of the nicest plastics to mess with. It has an extremely wide temperature range in which it is moldable but not liquid. It softens at about boiling of water and the liquidus is over 400F so it doesn't suddenly slump into a mess if you add a little too much heat.

            PET-G soda bottles aren't virgin material and they don't mold as nice as the pure stock. I have sheets of the virgin stuff for future experiments including one 4x8' sheet of 0.100" thick material. PET-G is nearly as strong as Lexan but unlike Lexan doesn't need to be pre dried before before molding thin sections. It also can be bent like sheet metal in a brake without cracking and it doesn't turn white at the bends.

            PET-G is very good for droop molding such as this nearly optically perfect dish shape. It's excellent for making replacement instrument crystals.

            Free software for calculating bolt circles and similar: Click Here

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            • #7
              Thanks guys, glad you liked it. Not only does the stuff do a great job, it's dirt cheap too. Did I say I like cheap...yeah, I love cheap. I'd still love cheap even if I was rich!
              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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              • #8
                Originally posted by Evan
                PET-G is very good for droop molding such as this nearly optically perfect dish shape. It's excellent for making replacement instrument crystals.
                What is an instrument crystal? Google fails me.
                Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                • #9
                  Originally posted by Black_Moons
                  What is an instrument crystal? Google fails me.
                  -Like the protective glass cover over the face of a watch or dial indicator.

                  Nicely done ducting, DB. Poor man's vacuum forming.

                  Doc.
                  Doc's Machine. (Probably not what you expect.)

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                  • #10
                    hot air gun to form?

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                    • #11
                      Neat job,I like it,I'm guessing with a bottle cap adapter and some air pressue the bottles could be blow moulded into other shapes as well.
                      I just need one more tool,just one!

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                      • #12
                        Originally posted by mike os
                        hot air gun to form?
                        Yes, I use the gun left over from covering model airplanes with MonoKote heat shrink iron on covering but any heat gun should do.

                        You shove the plug all the way in and start shrinking at the open end to capture it and then do the rest. Easy as pie!

                        Vacuum or blow molding would work as well but the mold would need a better finish if you were making something that needed to look good. You can make numerous shapes and sizes from different bottle sizes using the same method. Smaller plugs can be used by gluing on a spacer to make sure the plastic shrinks tightly around it.

                        Here's some pics of some model airplane parts I made back in the day.









                        The one on the left in the last pic looks a little wierd because it's a gyrocopter and needed a bunch of downthrust, hence the odd downward angle.
                        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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                        • #13
                          In your pix of the final product the fan inlet (outlet?) seems rather
                          close to the chip making end of the mill/lathe heads. If the fan is
                          blowing I would be a bit concerned about chips being blown through
                          the motor. The motor has a large PM cylinder that would glom up
                          any ferrous chips and be a mess to clean out. Not clear that any
                          metallic chips would be good for the brush/commutator interface.
                          Treadmill motors are pretty wide open at both ends. Plastic chips
                          would just tend to clog up the airflow over time.
                          Steve

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                          • #14
                            Thanks Steve...I was already planning to add a fine mesh screen to the inlet side to keep out the swarf. I may use some foam filter material I squirreled away in the shop somehere if I can lay hands on 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

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                            • #15
                              Something to keep in mind, if the motor is getting exceedingly hot off load, it will get even hotter on load, the heat in a DC motor is produced by the armature, not the stator, so by the time the heat has reached the stator, the armature heat is very much higher.
                              Max.

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