Surface plate resting pad source?
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  1. #1
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    Default Surface plate resting pad source?

    Dad has had a 24"x36"x4" toolroom grade surface plate for probably ten years now, but it's wooden crate is still covering it as it sits on the steel stand.

    Recently I picked up a B&S vernier height gauge, a Starrett No.258 Digi-Chek and other assorted surface plate-oriented goodies for him. I want to uncover the plate and ditch the wood, level it and actually see it being used now that he's got a surface grinder.

    The steel stand this piece of granite came with doesn't seem to have any of the dense (rubber?) pads at the airy points this rock should be sitting upon. Any idea what to use and where to get them? I've searched Starrett's site but found no useful information. Any ideas?

    Thanks!

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    Lightbulb

    Simplest item to find is the small machine leveling feet that swivel. The pad should not be resilient. That's the reason for using machine feet, since they're designed to support significant weight without deforming.

    Mount them upside down with the feet against the plate. You should use three of them.

    - Leigh

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    I'm going to respectively disagree. In looking over as much information as I could find on the internet, I discovered that the Starrett granite surface plates of that size are fitted with pads made of some type of resilient or "compliant" material. This is also what I've seen in looking at some other plates already installed at other shops.

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    It really depends on personal preference, in my opinion, and how obsessive you wish to be. If you select a compliant pad material, you should simply expect that over some period of time, compression and creep will occur, reducing the effective thickness of the material. Compensate by buying something thicker and/or denser. This type if installation will also allow slight chages in plate leveling to occur over a time span, but they will be small for this scale of installation.
    The swivel pad/hard mount is an excellent method for having zero change in Z location, so when it's leveled, it stays that way.
    It should be that the compliant pad will allow for better compensation in linear thermal expansion and contraction in an uncontrolled, or less well-controlled, shop environment. Lastly, if the plate and stand are on wheels, and subject to being moved around, the compliant pad mounts function somewhat as shock absorbers, making the plate less likely to crack or break(!) when rolling it over those big joints in the concrete.
    I use compliant pads for my setups at work, and actually have 4 pads on the larger of the 2 plates, just for stability. I don't think that the compliant material will overconstrain, and 4 compliant pads will compress to some sort of equilibrium over a short time in any case. McMaster-Carr has avariety of rubber washer/bumper type items to sort through.

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    I've seen surface plate pads made of hard rubber, phenolic, rubber inserted gasket material, steel, fabeeka, wood from pine to hard maple, plant fiber. Most anything else you can think of that doedn't rot would work, I imagine.

    All that's required of surface plate Airey point pads is presence. Stability Vs compliance can be debated endlessly. I prefer steel pads bonded with epoxy or elastomer adhesive. If I really have my druthers I like leveing jack screws and a rigid stand so I can level the surface plate should I wish to. I'd also like four anti-tip blocks at the corners so heavy parts won't tip out the surface plate and corner stops so the plate won't slip sideways over time.

    How about plopping your plate on a welcome mat?

    I see this thread going on for 4 pages as each partisan weighs in with personal preferences. I got mine in early; did I win anything?

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    Quote Originally Posted by Forrest Addy View Post
    I got mine in early; did I win anything?
    nope


    Tom

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    I use hockey pucks. Very solid, durable, easily obtainable, and a couple bucks a piece.

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    +1 on the hockey pucks. Bench levelers will work, too.

    Woodworking Assembly Hardware - Bench Levelers

    It's a rock, not rocket science.

    Edit: Here's "The Real Leigh's" Airy points map:

    http://www.practicalmachinist.com/vb...5/#post1317595

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    Thanks to all for the input. The matter is absolutely settled, so no further debate is required.

    When I went over to visit dad and his shop yesterday, he showed me how he had leveled it using 1/8" hard rubber pads in the four corners of the stone and using the screw-type leveling feet of the steel frame. And that is where the plate is going to stay for as long as dad is on this earth. It's his rock, his shop, he spent hours doing it, he's happy with it and I ain't going to move it. Period.

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    I may have missed something here, but why worry about a 24x36 chunk of rock. Level is nice but usually you are looking for a true flat surface to indicate from. If the deck of the stone is flat you could use it on a 45 angle. Get the stone setting as level as possible and carry on, if it twist out of shape, it wasn't worth the time you spent on it. Unless you are laying out the main frame for the space shuttle, get on with it.

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    I have a 24"x36"x4" and a (acquired on Friday last week) 36"x48"x6" Crown Windley surface tables. Both are on the makers original stands. Both have three point suspensions, plus two anti-tipping supports at the "pointy end".

    Neither is supported at the Airy points. The suspension points should, ideally be those that were used when the plate was ground/lapped, which may vary depending on the manufacturer.

    And, as Tailstock says, for a 24"x36" granite plate, it probably makes very little difference for normal workshop use.

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    Forest - You have won my never-ending admiration. That, and a couple of bucks, will get you a cup of coffee!

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    tailstock,

    What you missed is that some comparative measurements are most conveniently done with a precision level. The rock has to be level to begin with to use this technique.

    I'm doing that right now to refurbish a lathe saddle. I can use a surface gage, but it is slow and troublesome. The setup requires reaching over obstructions and that means the indicator is extended a long way from the base of the surface gage. The surface gage has to be lifted several times to reach everywhere and the many required approach angles include using the surface gage from all four corners of the flat. With all this motion and disturbance, repeat readings to less than .001" are not routine, which means I have to constantly recheck. It is so much easier, and faster, to go back and forth between scraping passes and checks if I use the level.

    I could also solve the problem with a larger flat and a more rigid suspension of the indicator, but reliable parallels and a precision level are at hand, so that is what I am using.


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