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Thread: How much is too much ?(weight)

  1. #1
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    Nov 2007
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    Default How much is too much ?(weight)

    I have a customer that I've been doing turnings for , they need a colum 8"dia with 1"x1/2"deep flutes. It would be a hollow turning , but still a lot of weight. I have the 6" indexer on my PRS Alpha. I was woundering if that would be too heavy.Oh yea the walls would be 1 1/4"thick , about the same volume of wood as a 6x6x72" solid post

  2. #2
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    Feb 2006
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    I think you'll be alright if you keep the indexer rotation speed moderate. Compare the circumfrence of the workpiece to the indexer rotation speed (deg/sec) and calculate the true inch/sec. You can even experiment with the ramping speeds for the indexer to minimize the backlash.

  3. #3
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    Thanks Scott , I am now thinking of an indexer speed of 60rpm , that would be about 25" sec. with a stepover of .02" with a 1/2" round nose. May seem slow , but that should leave a good surface. ...and new bits all around.

  4. #4
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    Can the stepper accurately stop that much weight from turning at that speed?

    I don't know the answer to the question but that is the real question.

  5. #5
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    Joe... well now that is a good question. Maybe 30rpm?. It will be in continuos motion while turning to round , the flutes are straight , I think 30 or 60 rpm will be slow enough to position the blank. ...I think

  6. #6
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    I think it's not just the weight of the blank but the weight of the blank and the resistance of the bit in the cut that puts the strain on the motor. So if you take a reasonabe cut and since you are only using a portion of the bit for the cut at any one time you should be able to take a reasonable (rough)cut to get to your diameter then follow up with a shallow fine cut to get a good surface.

  7. #7
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    Hey Stephen,

    There's some information on calculating speeds in the ShopBot wiki. It's focused on people using regular lathes with a ShopBot, but the math is pretty much the same.

    http://shopbotwiki.com/index.php?title=CalcLatheSpeed

    Bill

  8. #8
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    Nov 2007
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    Jack , I plan on taking light cuts , .15-rough , .02 finish. At that slow speed I think i will get a good surface. There are only two posts , they can take all day. I'd rather take it easy on the equipment and take more time.
    Thanks Bill , I saved that page .
    The job is not due till the end of Feb , a little time to practise making staved posts.

  9. #9
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    Feb 2008
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    I have read in past posts that with loading heavier items in the indexer, you have to be carefull of not letting the weight turn the indexer motor. They claimed it would "fry" the system somehow. I don't know if this is a true fact/myth, but I have loaded many very heavy pieces and always taken extreme caution. It has been written that it's better if the conrol box is shut off while loading, and I would tend to agree.

    Jim

  10. #10
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    Mar 2006
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    Jim,
    I would disagree, using this reasoning. While the control box is on, it has control of the indexer and if you've ever tried to turn the indexer manually while box is on, it is almost impossible. For that reason your blank is held solidly when mounting. I have an alpha maybe that makes a difference?

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