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  1. #46
    Join Date
    May 2003
    Location
    Central Coast, NSW
    Posts
    3,330

    Default More progress and more questions

    Well I found the clutch motor too difficult to use and lacking too many features like reverse and overspeed protection. I therefore swapped it out for a servo motor. It’s a rather cheaply built little motor but it will do for now. This motor allows me to set minimum and maximum speeds and reverse direction.

    I’m still using the same ill-fitting belt and pulleys, but have decided to replace them as one when I’m happy with how it works. Till then I have had to add even more temporary blocks of wood and plywood.

    I also remade the turntable and got it running very smooth with no wobble. Unfortunately it’s made from hmr pine board (melamine faced) so it will absorb water and degrade fairly quickly.

    Two questions arise when considering this motor.
    1. As you can see the pulley on the motor is small and the one on the shaft is even smaller. This gives me a minimum speed of 245rpm at the turntable as the motors minimum speed is 200 rpm. If I replace the pulley on the shaft with a larger one then I will obviously be gearing it down and lowering the minimum speed. Does this automatically increase the torque (which is currently borderline at low speeds)?

    It seems intuitively correct to me to gear it down so the ideal turntable speed of 300rpm is achieved in the middle of the motors rev range.

    Also, how do I calculate required pulley and belt sizes. Let’s say I want to reduce the speed at turntable by half and don’t want to change the pulley on the motor but rather the one on the shaft. Do I simply double it’s circumference, and how do I reckon the belt size from that (with my minimal maths skills)?

    4E8A916C-2B8F-4703-B61C-D63F6C7E1576.jpeg

    Anyway, the need at this stage was to see how the wheel would perform with a lump of clay on it before making any refinements, but buying clay at Christmas on the Central Coast is impossible so I harvested my own from the back yard and processed it. Just enough to see how well the wheel works. We have a lot of clay, something that has been a problem trying to get an orchard going. The clay actually wasn’t brilliant for wheel work, but here it is, my first pot. I used the dry method for processing the raw clay, the wet method would probably have given me a more compliant medium as it would have removed the organic matter and the bush sand so I’ll try that next time - I just wanted immediate results today. I know it’s an underwhelming result but it made some shortcomings very obvious which was the intention.

    AF386C85-3DBB-41C5-8C0D-8627DD4C2BAC.jpeg

    Also, my first attempt at pottery. It’s kind of like wood turning but without the dust.

    Cheers
    Arron
    Apologies for unnoticed autocomplete errors.

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  3. #47
    Join Date
    Jan 2005
    Location
    Campbelltown NSW
    Age
    77
    Posts
    335

    Default

    Quote Originally Posted by Arron View Post
    Also, how do I calculate required pulley and belt sizes. Let’s say I want to reduce the speed at turntable by half and don’t want to change the pulley on the motor but rather the one on the shaft. Do I simply double it’s circumference, and how do I reckon the belt size from that (with my minimal maths skills)?

    Cheers
    Arron
    Speed is calculated from the motor speed and the ratio of the two pulley diameters. All the calculations you need are here including belt length.

  4. #48
    Join Date
    May 2003
    Location
    Central Coast, NSW
    Posts
    3,330

    Default

    Quote Originally Posted by apple8 View Post
    Speed is calculated from the motor speed and the ratio of the two pulley diameters. All the calculations you need are here including belt length.
    Cheers, thanks
    Apologies for unnoticed autocomplete errors.

  5. #49
    Join Date
    May 2003
    Location
    Central Coast, NSW
    Posts
    3,330

    Default

    Quote Originally Posted by apple8 View Post
    Speed is calculated from the motor speed and the ratio of the two pulley diameters. All the calculations you need are here including belt length.
    Cheers, thanks. That is an excellent resource.
    Apologies for unnoticed autocomplete errors.

  6. #50
    Join Date
    May 2003
    Location
    Central Coast, NSW
    Posts
    3,330

    Default

    So, given a motor pulley diameter of 64mm and a distance between centres of 280mm, if I target running the motor at 900 rpm I need a pulley of 190mm and a belt of 973mm (or nearby) to get the turntable spinning at optimum speed of 300 rpm.

    The target speed for normal running is just a guess of course, but one I’d like to reality check. Because my main issue is maintaining torque, does torque increase as you gear down. Is my thinking right that if I increase motor speed but gear down to reduce turntable speed then I increase torque, as compared to say a 1 to 1 ratio?
    Apologies for unnoticed autocomplete errors.

  7. #51
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    27,756

    Default

    Quote Originally Posted by Arron View Post
    So, given a motor pulley diameter of 64mm and a distance between centres of 280mm, if I target running the motor at 900 rpm I need a pulley of 190mm and a belt of 973mm (or nearby) to get the turntable spinning at optimum speed of 300 rpm.
    Yep (192 mm to be precise).

    The target speed for normal running is just a guess of course, but one I’d like to reality check. Because my main issue is maintaining torque, does torque increase as you gear down. Is my thinking right that if I increase motor speed but gear down to reduce turntable speed then I increase torque, as compared to say a 1 to 1 ratio?
    Yep basically correct. If the motor power does not change, less revs will result in more torque.

  8. #52
    Join Date
    Jan 2005
    Location
    Campbelltown NSW
    Age
    77
    Posts
    335

    Default

    Yes if the pulley is larger than the motor pulley the torque increases in the same ratio as the pulley sizes. Think of belt drive air compressors where the motor pulley is smaller than the compressor pulley.

  9. #53
    Join Date
    Dec 2019
    Location
    Vancouver Island
    Posts
    1

    Default

    If you have a drill motor or drill press with a 1/2” chuck you could chuck the shaft and turn it with the motor and then use the emery to work the shaft down.

    Another method is to strip the emery into into narrow strips that are a meter long then do a full wrap on the shaft and pull it back and forth, the full wrap helps to equally work and keep the shaft round. WD40 makes a good lube while doing this. We used to use this method for hand polishing crankshafts.

  10. #54
    Join Date
    Oct 2002
    Location
    NSW
    Posts
    1,610

    Default

    Whereabouts on the Central Coast?
    We have several packages of clay from when my daughter was interested in pottery...

  11. #55
    Join Date
    May 2003
    Location
    Central Coast, NSW
    Posts
    3,330

    Default

    Quote Originally Posted by arose62 View Post
    Whereabouts on the Central Coast?
    We have several packages of clay from when my daughter was interested in pottery...
    Sending pm
    Apologies for unnoticed autocomplete errors.

  12. #56
    Join Date
    May 2003
    Location
    Central Coast, NSW
    Posts
    3,330

    Default

    Hey Arose62, did you get my PM? I’m concerned you may not have received it.

    Cheers
    Arron
    Apologies for unnoticed autocomplete errors.

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