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Surface plate support quick question

Discussion in 'METROLOGY - MEASURE, SETUP & FIT' started by expressline99, Mar 15, 2017.

  1. expressline99

    expressline99 H-M Supporter - Premium Content H-M Supporter-Premium

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    I just read in an excerpt from a early 1900's book that it's best to support your surface plate in a 3 point configuration. The part I read didn't go into any detail at all about what this was about. So is this valid or a typo? I'm sure it was referencing cast iron plates. (I think.)

    Paul
     
  2. MonkMan

    MonkMan United States H-M Supporter - Premium Content H-M Supporter-Premium

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    Found this on Rock of Ages site.

    SURFACE PLATE SUPPORT

    In accordance to GGG-P-463c, Rock of Ages insures accurate readings of surface plates by supporting the plate properly on three support points. Three points are preferred and are located 1/5 the length and width from the ends and sides. Three supports are used because it is the only way to consistently support a surface plate object without the weight shifting from one leg to another. Any attempt to use more than 3 points may cause the plate to receive its support on various combinations of three points and the plate will settle differently and possibly deflect out of tolerance.

    Rock of Ages provides various options for supporting surface plates:

    • stationary stands with leveling screws
    • stands with casters
    • stands with casters and leveling screws
    All models with casters come with wheel locks as standard. Any working height can be specified to meet your application need.

    - See more at: http://www.rockofages.com/en/industrial/products/surface-plates/#sthash.zSMXeVRf.dpuf
     
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  3. ewkearns

    ewkearns United States Active Member Active Member

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    A plane is defined by three points, therefore is much easier to level. Personally, I would think one would find a surface plate on casters less useful than one carefully leveled and stable.
     
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  4. Tony Wells

    Tony Wells United States Vice President Staff Member Administrator

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    Read up on Airy and Bessel points. It explains why.
     
  5. Rustrp

    Rustrp United States Active Member Active Member

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    Given the weight and it's setup location, a surface plate on casters may expedite shop projects. Level isn't the primary purpose of a surface plate, although having one set up in the level position seems to jump out as important. My concern would be the possibility of it getting tipped over and damaged.
     
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  6. ewkearns

    ewkearns United States Active Member Active Member

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    Yeah, in my downsized shop, I'm looking at casters for a LOT of things, but I'm going to arrange them such that I can have a hardened point leveling the [whatever] against the floor.
     
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  7. Rustrp

    Rustrp United States Active Member Active Member

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    In many of the carts and movable frames I've fabricated I like the foot operated brake that has about 3/4" of travel to use on the caster side of the table.
     
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  8. expressline99

    expressline99 H-M Supporter - Premium Content H-M Supporter-Premium

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    So is there a possibility of tipping on a 3 point stand? I'm considering a 24 x 24 plate. Probably the heaviest thing I would put on it would be 30-60 pound cross slides.
     
  9. ferlum

    ferlum United States Active Member Active Member

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    This.

    Also, I came across this recently, shows some configurations the OP might find useful (including examples of the three support points).

    http://www.precisiongraniteusa.com/pdffiles/5502.pdf
     
  10. ezduzit

    ezduzit United States Active User Active Member

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    On a small surface plate I wouldn't worry about 3-point mounting. And I likewise wouldn't worry about it tipping, using a 3-point mount, as long as there was a full support surface just beneath the 3 points. Mine is 12" x 18" (IIRC) and sits on a rollaway cabinet.
     
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  11. Rustrp

    Rustrp United States Active Member Active Member

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    Three legged milk stools have been around a long time. :)

    As ezduzit stated, the support for the three points would be the important factor. Most of the signage I've seen on the work benches or carts in machine shops always detail a **DO NOT** preceeding a list, with some type of physical harm done if said action was ignored. I think by the very nature of the surface plate being a precision tool, logic says we treat it with care. With that said; I stopped using "Would you treat your tools that way?" years ago.

    I've seen plenty of surface plates supported on work benches and carts. I don't think I would be inclined to place one on a three point stand. Many websites show the plate inset into or surrounded by a protective frame to prevent a **what if**. My experience in fabrication is the employee struggle with when to use a level versus a square. It isn't necessary for the plate support to be precicely level, just structurally sound.
     
    Last edited: Mar 16, 2017
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  12. expressline99

    expressline99 H-M Supporter - Premium Content H-M Supporter-Premium

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    This is all great information thank you guys.
    Paul
     
  13. tertiaryjim

    tertiaryjim Active User H-M Supporter-Premium

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    I would think a cart should have a frame slightly larger than the plate so the plate couldn't bump anything as it's rolled around.
    You could still mount the plate on three points with a square or rectangular frame and support the frame with four wheels.
     
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  14. todd774

    todd774 United States Active Member Active Member

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    Leveling could be an important factor if you what to do some static balancing. As with 2 knife edge straight edges.
     
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  15. Rustrp

    Rustrp United States Active Member Active Member

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    Yes it would, but if the intent was to facilitate timeliness in a machining project(s) to save steps back to the surface plate, it isn't likely related to static balancing. There's multiple tasks where a surface plate needs to be level.
     
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  16. todd774

    todd774 United States Active Member Active Member

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    I suppose you could seat the knife edges on 4 posts. 3 of which are adjustable.
    The reason I even mentioned it was because I just very recently purchased a surface plate. I was thinking of how I should mount it. While planning it out in my head I realized I could
    Balance Harley Davidson fly wheels with that kind of set up. My original purpose of purchasing the plate was to scrape the ways of a cheap Chinese milling machine.
    Mine will also be on a heavy duty cart with casters.
     
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  17. expressline99

    expressline99 H-M Supporter - Premium Content H-M Supporter-Premium

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    Static balancing... well it's gone over my head again. lol
     
  18. Rustrp

    Rustrp United States Active Member Active Member

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    Imagine a round rod placed in the mounting hole of a lawnmower blade so you can tell which side needs to be ground down to balance the blade. Something requiring more accuracy might be the stone/wheel for a surface grinder. Static balancing would be the least expensive way to check for an out of balance condition, but it's also a quick way to answer a vibration question. e.g. vibrating bench grinder.

    PS. Okay, I just assumed you had balanced a lawnmower blade, or that you had lawn that needs mowing. :)
     
  19. Rustrp

    Rustrp United States Active Member Active Member

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    I did chuckle. I imagine a guy sitting on a Harley thinking; Hmmm, maybe my flywheel is out of balance. :D
     
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  20. todd774

    todd774 United States Active Member Active Member

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    If ya think about it, if you didn't know better the first time you sat on a Harley you'd probably say:
    "Hmmm, maybe my flywheel is out of balance. Maybe I need a surface plate"
     
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  21. Dabbler

    Dabbler Active Member Active Member

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    All of the higher end Standridge stands use two adjustable elevator bolts, and two more on a rocker arm, making the leveling as per a 3 point system, but supporting on all 4 Bessel points. For long term flatness, the surface plate (especially large ones) need to be supported equally on all 4 Bessel points. (.2204 from the edges, as I dimly recall)
     
  22. expressline99

    expressline99 H-M Supporter - Premium Content H-M Supporter-Premium

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    >.2204 from the edges... are you a suspect for photographic memory?

    So after re-reading all this is it a yea or nay for 3 points? It sounds like on the large plates (3'x3' Or bigger?) that they need 4. At the largest I would have a 3' x 3' . I just wonder at what width or thickness would it start to flex, twist or distort. If I'm using it to scrape small ways my wooden workbench might not be where I want to set this thing up. I know my garage floor is bowed like >insert anything you want here< . I know I won't have a Harley in there. So I guess I'm still up in the air on this. Then it gets back to will I ever get my work to a level quality that would require this amount of OCD in advance. :chemist: Perhaps!

    Paul
     
  23. ddickey

    ddickey United States H-M Supporter - Premium Content H-M Supporter-Premium

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  24. Dabbler

    Dabbler Active Member Active Member

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    I have 3 surface plates, and here's what I'm doing with them:

    - an 11"X 9"X2.5" (unknown grade) from China - used only as a bench plate, for lapping only. supported by bench. stored in a drawer.
    - a 12"X18"X3", (B grade) - just unmounted it from its stand, because I'm reusing the stand. It will be mounted on 3 points, just because it's easier.
    - a newly acquired 18" X 24" Mitutoyo A grade plate. see below...

    ... first a short story: I have a friend that bought a Mitutoyo AA grade surface plate in the 36 X 48 X 5 inch size - and mounted it using the 4 corners... After 36 years, it has dropped about .006 in the centre. It is now worse than a shop grade plate. I wouldn't take it if he gave it to me.

    So being a little OCD and/or anal-retentitive (yes it does have a hyphen BTW), and because I'm not from Standridge Granite I am mounting my new surface plate on a rolling Tool and Die cart, also recently acquired, which is made of 10 gauge pressed steel. The plate will be mounted using 4 Bessel points with a pivot...

    The best advice I can give to you is that if you are mounting it on a non-movable table, make the feet of the table adjustable so ti is properly supported( so the table won't twist) . No use twisting your surface plate for the lack of 1$ worth of leveling bolts. If it is on a moving base, the your plate's sub-base must be overly rigid, so as to support the plate properly. No matter what, the plate has to ber very rigidly supported to maintain calibration.

    3 or 4? your choice - if your manufacturer won't commit, I'd use 4. If you go with a Standridge 24 X 36, they explicitly say use 3 because they calibrate them that way. I hope this is more helpful than confusing,...
     
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  25. expressline99

    expressline99 H-M Supporter - Premium Content H-M Supporter-Premium

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    This guy is great. I'm surprised he wasn't on my subscribed to list.
    Paul
    Unreal how multi-million year old granite moves in a few years. This does help me quite a bit. I'll have to buy some really ridged box tubing to weld up once I select a plate. I've got a lot of measuring equipment to purchase going forward. Seems the surface plate is the base point for being able to measure with accuracy.

    Being as new to it as I am I've got a long way to go. Since there is never an end to the learning on this topic I think I've picked the perfect hobby.

    Paul
     
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  26. Rustrp

    Rustrp United States Active Member Active Member

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    Yes there is! Door #3 has a tunnel with an infinite length filled with infinite cubby holes just waiting for someone to say; "I didn't know that."

    Now, I'll say I was with him up to the point where he puts a beam on the third support. I still think we get stuck thinking **level** when all we are really striving for is flat. The plate is certified (if it is of certifiable quality) and it needs to be supported so there's no force or tension on any specific point. I don't think there's been proof that a plate supported on three points ends up with to of the corners drooping. I think if we replace the word support with suspend we arrive where we need to be.

    With that said, I wouldn't want the workbench or support to be out of level to a point where things roll off the plate.
     
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  27. Tony Wells

    Tony Wells United States Vice President Staff Member Administrator

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    I think if I ever get room and need for a larger plate, I will build a heavy stand with leveling feet, just because it may have to move some time in the future.....never know. But I will build the top as a tray and fill it about an inch deep with self leveling floor compound. That stuff seems to flow out really nicely and should give even support. HOWEVER, the catch is that there is no guarantee that the top and bottom of any plate are parallel, nor that the bottom is actually flat. But if I time it right and sit the plate in the compound just before it sets up, then I would have virtually 100% contact and therefore support for the entire plate. It wouldn't matter so much if it weren't perfectly level at that point, as I would adjust it with the feet. It doesn't have to be level, but it sure is nice at times to have a known level surface. And I mean really level, so close I could use it (to a degree) to calibrate levels. Like the one I'm about to build as soon as I talk Ken into scrounging me a piece of nice, aged CI.
     
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  28. ezduzit

    ezduzit United States Active User Active Member

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    TW--that is bound to fail as changes in the mounting surface will impart stress on the surface plate. If that were a workable solution, the big guys would be using it already.
     
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  29. expressline99

    expressline99 H-M Supporter - Premium Content H-M Supporter-Premium

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    OK to take this a step beyond this. Could you mount the surface plate support system in a way that it would be stabilized and protected from vibration. Much like they earth quake proof buildings? Almost in a stiffened rubberized mount that would take the stress or any expansion of the bench material?
     
  30. Rustrp

    Rustrp United States Active Member Active Member

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    There's no such thing as an earthquake proof building. :grin big::grin big:

    ....but we do keep trying.
     

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