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Airie and Bessel points

Discussion in 'A BEGINNER'S FORUM (Learn How To Machine Here!)' started by Moderatemixed, Aug 24, 2017.

  1. Moderatemixed

    Moderatemixed Canada Active Member Active Member

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    Hey everybody..... my second post in 2 days. Apologies, but to be honest, the experience level here is fantastic and I appreciate being able to draw from it. So I scored a Starrett 24" X 36" x 4" toolroom grade surface plate. I have read a bunch of posts here about how to mount it and really all that I have determined is that it should be supported at three points.

    Then it seems that arguing and sarcasm take over and the threads fall apart. So my plan was to take 9 hockey pucks and make three sets of 3 in three positions as feet (supports). I don't know if that is right or wrong but I can't seem to make heads or tails of what size supports to use and where do they go? I've seen .577 a couple other numbers but I have no idea what they mean. Perhaps someone would just tell me for example: use 4 inch diameter supports, put them 8 inches in from the end and 8 inches in from the front and back on the left side (2) and the one on the left side is 12 inches in from the back and 12 inches in from the right side....... essentially how do I mount it, please someone just tell me.

    Best regards to you all, and thanks in advance. Too, if someone knows where to clearly find an answer be it internet or machinist handbook, I am happy to check the reference.

    Cheers.

    Derek


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  2. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    Just do it like the people who make the plates do it. They know what they are doing. On the plate itself you want three mounting points and only three mounting points. Stand to floor, do what you want to... Still, you cannot go wrong with following the instructions on this page:
    http://standridgegranite.com/forms/installation-instructions
     
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  3. mikey

    mikey Active User H-M Supporter-Premium

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    Starrett's instructions are not as precise as Standridge is re placement; I would follow the advice in the link from Bob. Your hockey puck material is a good choice. Personally, I would cut it square to fit the width of the support bar of your table. By that, I mean if the bar the feet will contact is 2" wide then I would make the support pad 2" X 2". There is no size requirement for the supports as far as I know; only where they are placed.
     
  4. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    Many plates already have round plastic or wood plates glued to the bottom of them in the correct locations, typically around 2" in diameter and 1/4" thick, to keep point shock loading from damaging the plate and to help spread the point loading a bit.
     
  5. mikey

    mikey Active User H-M Supporter-Premium

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    Aah, what do I know. I'm using 1/2" X 1" pieces of my wife's cutting board and it works fine. :)
     
  6. Moderatemixed

    Moderatemixed Canada Active Member Active Member

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    Ok great! Thanks gentlemen! The plate is sitting on a 2.5 inch thick solid walnut benchtop. I will use 3 pucks squared accurately in the lathe. The plate doesn't have the spots marked unfortunately. My plan then will be look at the Standridge guidance and see what it says for positioning. Not that my level of accuracy will ever warrant the effort but if you are going to go to the trouble of doing something you might just as well do it as best as you can. Cheers guys!


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  7. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    Standridge gives a range of mounting position locations that will work well. There is probably 2-3 inches of latitude for where you position the mounts in each direction on your 24x36 plate. Follow the guidelines and all will be good.
     
  8. Moderatemixed

    Moderatemixed Canada Active Member Active Member

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    I have it sorted out. Starrett also puts out some good directions that I had not found to this point. Regards all.


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  9. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    Probably this one:
    12) How should my surface plate be supported? Does it need to be level?

    A) A surface plate should be supported at 3 points, ideally located 20% of the length in from the ends of the plate. Two supports should be located 20% of the width in from the long sides, and the remaining support should be centered. Only 3 points can rest solidly on anything but a precision surface.

    The plate should be supported at these points during production, and it should be supported only at these three points while in use. Attempting to support the plate at more than three points will cause the plate to receive its support from various combinations of three points, which will not be the same 3 points on which it was supported during production. This will introduce errors as the plate deflects to conform to the new support arrangement. All Tru-Stone steel stands have support beams designed to line up with the proper support points.

    If the plate is properly supported, precise leveling is only necessary if your application calls for it. Leveling is not necessary to maintain the accuracy of a properly supported plate.
     
  10. Moderatemixed

    Moderatemixed Canada Active Member Active Member

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    You nailed it! Cheers.


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  11. Wreck™Wreck

    Wreck™Wreck United States Active User H-M Supporter-Premium

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    You are thinking way to hard, are you making parts that have to work in an assembly consisting of many parts made by many different vendors thousands of miles apart?
    If you do such work a reliable surface is quite useful. On the other hand if you a banging out plain bearings for the neighbors 1969 Dodge Dart control arms you do not need a surface plate at all.
     

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