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  1. #1
    Join Date
    Nov 2015
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    Brisbane Australia
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    85

    Default Speed calculator on a dial for a lathe

    As you do on a rainy Friday night I was perusing through the used lathes on ebay and came across a Swedish lathe with a great idea, I have not seen one before but it does imperial feet/ minute and metres/ minute.
    You move the dial to the diameter and cutting speed for the metal, rotate to suite and it tells you on the bottom how fast to have the machine.
    Being the novice I am I think it is a great idea.

    Screen Shot 2019-03-15 at 20.37.35.png


    Maybe the picture didn't come out but here is the link to the Ebay page
    If you zoom in on the left you will see what I am talking about.

    Big Metal Lathe - BOSS says SELL CHEAP | eBay

  2. #2
    Join Date
    Aug 2008
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    near Rockhampton
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    6,216

    Default

    The Macson 18/21" swing lathes had a dial thing on the headstock. I think it was some sort of spindle speed calculator.
    Attached Images Attached Images
    Gold, the colour of choice for the discerning person.

  3. #3
    Join Date
    Nov 2010
    Location
    Gippsland Victoria
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    733

    Default

    If you like it you could maybe make one out of two pieces of paper or cardboard and keep it beside your lathe.

    I've seen another graphical calculator you might find useful with material type, cutting speed and diameter shown on three straight parallel lines knowing any two you can draw the line connecting two points to estimate the third

    https://vanhack.ca/lib/exe/fetch.php...ting-speed.png

    Am sure it is in one of the basic beginners turning books but cannot find it on my shelf, the above link shows a version of it.

    This sort of graph is called a nomogram. Have done some googling but cannot find the version I am thinking of.

    Bill

  4. #4
    Join Date
    Oct 2011
    Location
    Norwood-ish, Adelaide
    Age
    59
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    6,540

    Default

    Here's another one
    Speed calc.jpg
    At one stage I was going to make a copy but I find (especially with my lathe) that just because you can run work that fast does not mean it is practical - flex, chatter, shape all conspire to mean that you need to cut speed.

    Michael

  5. #5
    Join Date
    May 2011
    Location
    Murray Bridge S Aust.
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    71
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    5,942

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    That's a good point Michael, but for a beginner, it's a good starting point, as it would vary according to the lathe, overhang of the tool, and many other variables.
    Kryn
    To grow old is mandatory, growing up is optional.

  6. #6
    Join Date
    Aug 2011
    Location
    Melbourne
    Posts
    4,779

    Default

    When I first started turning I felt I really needed a quick and easy spindle speed guide, so I made up an excel spread sheet and printed it out. The horizontal rows had the desired speed in M/min, the vertical columns had the diameter of the material and the corresponding cell contained the required RPM for the correct surface speed.


    I hardly use it now. I go by initial guess and then feel.


    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  7. #7
    Join Date
    Aug 2008
    Location
    Melbourne
    Age
    34
    Posts
    1,075

    Default

    Here's the nomogram from the standard TAFE textbook "Fitting and Machining"

    IMAG3239.jpg

    What I really want is a feed chart; I can usually pick a good speed, but getting the chips to break nicely and leave a good finish as well is still very hit-and-miss for me.

    It seems to be affected by tip radius as well, are there any rules-of-thumb?

  8. #8
    Join Date
    Jun 2007
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    sydney ( st marys )
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    Default

    Don't exceed the nose radius.

  9. #9
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    Aug 2008
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    Melbourne
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    But the only way I'm getting a bright finish is by going deeper than the nose radius

    0.5-1.0mm deep on a 0.4 rad comes up better than grinding, but 0.2 deep on the same tool comes out chewed up and horrible.

    EDIT: Never mind, that's depth, not feed.

  10. #10
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    6,439

    Default

    Quote Originally Posted by simonl View Post
    When I first started turning I felt I really needed a quick and easy spindle speed guide, so I made up an excel spread sheet and printed it out. The horizontal rows had the desired speed in M/min, the vertical columns had the diameter of the material and the corresponding cell contained the required RPM for the correct surface speed.


    I hardly use it now. I go by initial guess and then feel.


    Simon
    Hi Simon,

    That is a good skill to learn ! Its surprising how many tasks where you can take advantage of that skill.
    Best Regards:
    Baron J.

  11. #11
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    Jun 2007
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    sydney ( st marys )
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    Quote Originally Posted by elanjacobs View Post
    But the only way I'm getting a bright finish is by going deeper than the nose radius

    0.5-1.0mm deep on a 0.4 rad comes up better than grinding, but 0.2 deep on the same tool comes out chewed up and horrible.

    EDIT: Never mind, that's depth, not feed.
    If you have the HP you can go 2/3rds the the length of the cutting edge.

  12. #12
    Join Date
    Nov 2007
    Location
    melbourne australia
    Posts
    3,228

    Default Speed calculator on a dial for a lathe

    I did similar to Simon when I started out. Fitted a tacho to the lathe and made a table of RPM vs stock diameter for various materials. Not long after I removed the tacho and threw out the table. I now make an educated guess of RPM based on the type of material, its diameter and the tool doing the work. Set the VFD and start cutting. Adjust RPM as required to give a nice finish or stop the chatter when parting off.

    I actually found some of the recommended speeds and feeds didn't work. I suspect they are designed for much more rigid machines than my Hercus 260.
    Chris

  13. #13
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    Jun 2007
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    sydney ( st marys )
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    Default

    It's theory.

  14. #14
    Join Date
    Nov 2010
    Location
    Gippsland Victoria
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    733

    Default

    Quote Originally Posted by elanjacobs View Post
    But the only way I'm getting a bright finish is by going deeper than the nose radius

    0.5-1.0mm deep on a 0.4 rad comes up better than grinding, but 0.2 deep on the same tool comes out chewed up and horrible.

    EDIT: Never mind, that's depth, not feed.
    I often get a very good finish by turning the knife tool around to present a flat edge to the workpiece and take a tiny fluff cut. Sometimes doc can be as little as pushing slightly on the toolpost with my hand.

    If you want to be geometrical about it that is an infinite tip radius and a microtadge depth of cut.


    Bill

  15. #15
    Join Date
    Aug 2007
    Location
    Saskatoon, Saskatchewan, Canada
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    Default

    Search for machining apps and download one or two to your cell phone. Some basic ones are free and the better ones cost a few bucks. Now you have the info for lathes, milling, drilling, tapping and shop math in your pocket. They are designed for industry and carbide so you may want to be less aggressive depending on your machine but they get a newby like me in the ball park.

    Pete

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