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  1. #1
    Join Date
    Apr 2009
    Location
    Kingswood
    Posts
    930

    Default Harrison M250 Motor Belt Problems

    When first acquired, the motor pulley had problems and a new pulley made.
    Several years have passed with great performance from a VFD.

    Recently, I occasionally get 'bump' noises.

    Investigation reveals the 'bump' is associated with the belt.
    I can initiate the bump by leaning on the motor to increase the belt tension.
    The tension adjustment is one-way only using a pivot shaft and jacking screw, so easy to lean on it to increase then tension.
    It seems to be associated with the belt passing around the motor pulley, always the same part of the belt.
    The belt appears to be constant in section and appearance throughout its length.

    Do belts have localized stiff areas that flex differently to the general belt performance ?

    Tomorrow, I will increase the belt tension, check belt details and order a spare.

    This post is just a general inquiry for any suggestions of specific inspection, test or investigation aspect that might be followed.

    Keep well,
    John.

  2. #2
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    6,439

    Default

    Hi John, Guys,

    When I did the bandsaw refurbishment, because I made a new motor mounting plate, I needed a new slightly longer belt. I got one that was intended for a car water pump. From new it had a lump in it. I later bought a Fenner belt and that runs perfectly smoothly.

    I cut the water pump belt up and found that they used a round cloth like dowel to make a join, this bit of the belt is fatter than the rest of it and caused a bump and also caused the motor to kick each time it hit the pulleys.
    Best Regards:
    Baron J.

  3. #3
    Join Date
    Jan 2004
    Location
    Mackay North Qld
    Posts
    6,446

    Default

    Hi electroseam,

    Could it be from the lathe sitting inactive in the cold weather for a time?

    The belts, like the tires of a car that has sat around for a while, take on a shape and its noticeable when the car is driven.

    Is a similar thing happening with the lathe belt ?

    Perhaps not flat spot like the car, but basically,the belt taking on a a semi permanent new shape .

    Time will tell perhaps when you obtain a new belt and fit it.

    Grahame

  4. #4
    Join Date
    Oct 2004
    Location
    Southern Highlands NSW
    Posts
    1,894

    Default

    When the replacement pulley was made, did it take into account its diameter?
    As I understand it, there are different V angles suggested, according to how much the V-belt is to bend around the pulleys.
    The cross section shape of the belt does not remain constant, but changes as it bends, the more so the greater the bend.
    You might get better performance with a different belt, such as one of those that have notches, which I think help maintain their shape.

  5. #5
    Join Date
    Nov 2017
    Location
    Geelong, Australia
    Age
    57
    Posts
    2,651

    Default

    Thanks Nadroj - one of those snippets that's only obvious once you know about it.
    Its going to be a good day - only 8am and I've already learned something.

    Steve

  6. #6
    Join Date
    Sep 2008
    Location
    Riddells Creek, Vic.
    Posts
    831

    Default

    Quote Originally Posted by nadroj View Post
    When the replacement pulley was made, did it take into account its diameter?
    As I understand it, there are different V angles suggested, according to how much the V-belt is to bend around the pulleys.
    The cross section shape of the belt does not remain constant, but changes as it bends, the more so the greater the bend.
    You might get better performance with a different belt, such as one of those that have notches, which I think help maintain their shape.
    If you are referring to the angle of the V in the pulley, that would require custom made pulleys for each application. A V groove in a standard pulley has an angular tolerance of a few degrees.

  7. #7
    Join Date
    Nov 2017
    Location
    Geelong, Australia
    Age
    57
    Posts
    2,651

    Default

    Quote Originally Posted by Techo1 View Post
    If you are referring to the angle of the V in the pulley, that would require custom made pulleys for each application. A V groove in a standard pulley has an angular tolerance of a few degrees.
    Sounds like you're thinking the degree of wrap is involved, but its only the diameter that controls the angle.
    I'd always thought they were just a tolerance, but a bit of research online turns up consistent info that smaller diameter pulleys need to be at the smallest angle (34deg for an 1.5" A section) and then increasing up to 38deg for 7" diameter and over.

    Steve

  8. #8
    Join Date
    Apr 2009
    Location
    Kingswood
    Posts
    930

    Default

    The belt taking a set overnight in cold weather will be checked.

    Pulley size and shape was carefully considered before manufacture and, as mentioned in the first post, the belt has performed faultlessly for a few years.
    The belt does have notches at the bottom.

    Inspection does not reveal visually any variations in the belt but, a DTI picks up a sideways bulge as the belt tracks past the DTI (slowly !).
    A chalk mark at the 'bulge' coincides with the 'bump' as it passes around the motor pulley.
    One can also see the belt track higher up the V groove as the 'bulge' goes round.

    A new belt will be purchased but, progress will be slow as are other projects are keeping me busy, and the lathe is usable.

    John

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