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Thread: Fan Duct !

  1. #1
    Join Date
    Sep 2012
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    Thumbs up Fan Duct !

    Hi Guys,

    I decided that it was about time that I got my finger out and finished making a fan duct to go on top of the motor on the mill.

    These DC motors get hot quite quickly and since all the heat is effectively trapped in the armature windings and it can only slowly escape via conduction through the spindle and top and bottom bearings. In addition to a very poor fan on the armature shaft sucking air in from the bottom and it being passed up the inside of the motor frame, providing not much cooling at all. Due to the centrifugal action of the spinning armature forcing the bulk of the air flow outwards and up between the gap inbetween the field magnets, I though that an auxiliary fan would be of benefit.

    Also having a suitable 12 volt fan, wall wart, some PVC pipe and a tin of pvc cement decided to make a cooling system that sat on top of the motor and sucked the hot air out. This is what I came up with !

    06-05-2021-001.JPG 06-05-2021-002.JPG

    I trepanned the centre out of this piece of plastic material on the lathe using a piece of 1/16" by 5/16" HSS that I had. I mounted the piece of material on a 1/4" mandrel and cut from both sides.

    06-05-2021-007.JPG 06-05-2021-006.JPG

    I had some PVC pipe which was a little too big so I cut a slice out and used it to hold the gap together whilst the adhesive set. As can be seen I used a couple of tie-wraps to hold things in place. I made this pipe weeks ago but other things got in the way.

    06-05-2021-005.jpg 06-05-2021-004.JPG 06-05-2021-003.JPG

    This is how it looks now. The four mounting screws thread into the corner holes in the fan. The fan runs at 3K rpm and shifts a lot of air. I'll post a picture of it on top of the motor later, the camera battery went flat on me before I got chance to take its photograph.
    Best Regards:
    Baron J.

  2. #2
    BobL is offline Member: Blue and white apron brigade
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    Default

    Neat - I've made a few fittings like that.

    WHen I had to make quite a few I even made a flange junction former as a heat mould to use on my woodie lathe.
    Former.jpg
    35 mm ring of PVC is pushed onto the former and heated with a hot air gun and pushed onto the flared end using a segment of PVC.
    Method.jpg

    Then it's removed from the former and further heated and pushed over a room temp piece of PVC
    Flangeb.jpg

    Here is one using a very high radius of curvature formed directly onto the end of a segment of PVC.
    IMG_1924.jpg

    One thing I've noticed is that given that ~90% of the air flow from a prop type fan comes from the outer 20% of the tblades it looks like you are blocking most of the air flow ?

  3. #3
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    Hi Bob, Guys,

    Thanks for the pictures in your post, very interesting technique !

    One thing I've noticed is that given that ~90% of the air flow from a prop type fan comes from the outer 20% of the blades it looks like you are blocking most of the air flow ?
    I agree ! However the device is intended to sit on top of the mill motor with the fan on top sucking the air out of the quite small vents in the top of the motor case. Anyway this is the only 6" inch, 12 volt fan that I have.

    I had considered making the air tube fit over the diameter of the motor so the air got pulled from around the outside as well, but decided that since all the heat is contained within the armature and conducted out to the motor frame via the bearings, it would be more effective to pull the hot air out and rely on cooler air flowing up the inside of the motor.
    Best Regards:
    Baron J.

  4. #4
    Join Date
    Sep 2012
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    Hi Guys,

    Just a couple or three pictures of the duct and the top of the motor so you can see what path the air flow has to take to get out of the motor.

    07-05-2021-001.JPG

    This first picture is the duct on top of the mill motor showing how it just sits sucking the air out.

    07-05-2021-003.JPG 07-05-2021-002.JPG

    These two show the total amount of venting and the duct sat on top of the motor. The vents on the bottom motor casting are exactly the same. Just to give an Idea of size that motor cap is 3.75 inches in diameter and those slots are 6 mm wide.
    Best Regards:
    Baron J.

  5. #5
    Join Date
    Sep 2006
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    Australind , WA
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    Default

    Looks good John.

    Sent from my SM-G970F using Tapatalk

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