Cast Iron Surface Plate
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  1. #1
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    Default Cast Iron Surface Plate

    A friend of mine made me a 16" diameter by 2" thick cast iron surface plate. It was supposedly lapped "optically flat". It has a mirror bright finish. I have not checked the flatness of the plate myself.

    The question I have is should I work with this plate or buy a cheap granite plate? It is for an armature home shop.

    If I do use it what do I have to do for the use, care and maintenance of a cast iron surface plate?

  2. #2
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    Quote Originally Posted by BigAl666 View Post
    If I do use it what do I have to do for the use, care and maintenance of a cast iron surface plate?
    1) Don't get it wet.

    2) Don't feed it after midnight.

    Welcome to PM. We have no idea how flat your plate is (shiny does not equal planarity), and CI is subject to dings, rust, etc. So save that plate until you can get it measured and buy a cheap granite surface plate, even the CN B-grade plates are typically pretty good.

    Granite is a better "rubbing" surface in many instances when using height gages and the like, so they'll move more smoothly than on a CI plate.

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  4. #3
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    Does your friend make telescopes? If so, he may be able to tell you just how flat it is- and it is likely far more flat than what you need- but that is what you want. Having a surface that is less accurate than claimed or needed is a problem.

    I would get an inexpensive plate to use for "close enough" noncritical work, and save the good plate for when it is needed.

    Be aware that if you lay the lapped surface down against another lapped surface the air will be forced out. As this occurs the surfaces will easily slide- but after they are fully touching they will be very difficult to separate.

  5. #4
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    Its probably not worth a damm, It would need to be a lot thicker to hold its flatness, and it takes a very good stable grade of cast for a surface plate, I have one that is 18x24 and it is webbed and 6 inchs thick, 450 lbs. Your plate would be all over the map with a change in temp. Find a pink stone....Phil


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