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

    Default Lathe V-belt PCD Rating

    My recently acquired Harrison M250 lathe is fitted with a 2900 RPM 1.3 kW 3-phase motor and a headstock geared for a maximum spindle speed of 3000 RPM.
    When operated with an inverter at 50 Hz and maximum speed selected, severe belt slip on the motor pulley was noted.
    Inspection revealed severe wear of the aluminium pulley, it looks like it has been slipping for some time.

    The pulley has been machined down to achieve correct V-belt fit dimensions following advice to reduce the included angle in the pulley enclosed angle from the nominal 38 degrees to 34 degrees for small PCD pulleys.
    The outside pulley diameter is now 52 mm, giving a V-belt wrap diameter at the PCD of about 42 mm.
    This PCD is, I believe, borderline for the designated SPZ800 V-belt.

    Can anyone recommend an alternative to a standard belt that will operate at such a small wrap PCD ?

    Thanks in advance,
    John

  2. #2
    Join Date
    May 2012
    Location
    Kimberley, West Australia
    Posts
    176

    Default Belts and pulleys

    Hello John,
    A 52mm pulley is way below recommended size for what I assume is an A section belt, and an alloy pulley is only adding to your problem. Can you afford to step up to a 65mm pulley in cast iron, and have the option to reduce speed via your inverter drive, or use lower secondary reduction ratios? Forget alloy pulleys in small sizes. They are no joy at all.
    Once you have a cast iron pulley in your chosen size, select a belt in the automotive range, in the "cog belt" design. The ones with the teeth on the back are OK, but the ones with teeth on the underside are much better at conforming to small (undersize) pulleys. Less heat and more grip. If you get blank looks in the auto spares shop, go to a Caterpillar Spares department, and get the parts jockey to pull out a reference and cross-match book called "One Safe Source". They can match any industrial type to a Cat cog belt which will outlast most belts and won't be too damn expensive. Ran a range of machines on Cat belts and solved a lot of problems.
    You should be able to tighten a cog belt enough on the smaller iron pulley to transmit most of your 1.3kw without slippage. Ordinary industrial A section belts require a minimum of a 75mm pulley to avoid slippage, belt heating and destruction in continuous service. Hope this helps. Combustor.

    Oops! Just looked up your SPZ800 belt, realised it's only 10mm wide, not a 12 or 13mm A type. However, still recommend an iron pulley, bigger if you can accommodate it, not sure if cog belts go down to 10mm. Combustor.
    Last edited by Combustor; 4th May 2013 at 12:25 AM. Reason: Extra info.
    Old iron in the Outback, Kimberley WA.

  3. #3
    Join Date
    Apr 2009
    Location
    Kingswood
    Posts
    930

    Default

    Combustor,
    Thanks for the input, all your suggestions will be considered.

    I can easily use a bigger pulley, but that puts the top speed up also, and there is no room for a bigger pulley on the headstock.
    The Harrison M250 was only supplied for a short time with 3000 RPM spindles, they soon reverted to 2000 and 2500, presumably because the 3000 gave problems.

    But, I don't want to give up too readily on the spindle power by just reducing the VFD frequency.

    Still looking at catalogs, perhaps an 8mm wide belt (SPZ is 10 mm) would be OK in this application.

    John.

  4. #4
    Join Date
    Sep 2006
    Location
    Mallacoota,VIC,Australia
    Age
    53
    Posts
    1,010

    Default

    HI John,
    My first thought was a Cogged Belt, because a Cogged Belt will 'WRAP' itself around a small Pulley better than a plain belt. I just did a Google search ie SPZ800 V Belt cogged version and came up with XPZ800 which is a cogged belt and the dimensions appear to be the same. Personally I would be trying a Cogged Belt before I started changing Pulleys.
    I hope this Helps.
    All The Best steran50 Stewart

    The shortest way to do many things is to do only one thing at once.

  5. #5
    Join Date
    Mar 2009
    Location
    Blue Mountains
    Posts
    195

    Default

    Hello John,
    You could try a Z section belt, it is the same width and pitch size as an SPZ but is only 8 mm high as opposed to 10 mm for the SPZ. This allows it to go around smaller pulleys, down to 54 mm pitch dia. according to the standard I have (AS 2754-1985). The pitch dia. is measured at the pulley and belt width of 8.5 mm. These Z section belts are also called M section in some parts of the world and the way of designating length is also different but the cross section dimensions are identical.
    I am going to Penrith once a week at the moment and have a collection of Z section belts you are welcome to try, give me a PM if interested.
    Mm. (Phillip).

  6. #6
    Join Date
    May 2012
    Location
    Kimberley, West Australia
    Posts
    176

    Default Belts and pulleys.

    Hi again John,
    Sorry I went off on a sidetrack. Sounds like your alloy pulley is already out of time if it has been worn and re-machined. Steran50's suggestion of an XPZ belt sounds good. Tried looking up pulley suppliers for SPZ but did not readily find an Australian one. Any good belt and bearing shop should know where they are found. Sure I have seen similar on washing machines.Look in tips and junkyards or auto electrics.
    Another way is to get a 1440rpm motor, quiet and more efficient. 3 phase can be had for scrap price ex larger aircons etc. Then fit a 100mm pulley, at that size an alloy one will do the job. Could even fit an A pulley, groove it out deeper if needed. They are on every shelf. Hope you find an easy answer. Regards, Combustor.
    Old iron in the Outback, Kimberley WA.

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