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Another NooB Question...Granite Block

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  • Another NooB Question...Granite Block

    Today I picked up a 18"x24" granite surface plate for what I think was a decent (really cheap) price.

    Now, other than the obvious checking for flatness of various objects, what are other uses of a surface plate?

    OK, I admit it, my name is Dennis and I'm a tool-a-holic.

  • #2
    It also gives you a reference surface to make measurements from
    as in layout of rectilinear cutting/drilling or boring patterns. Height gauges
    are typically used on granite plates for this purpose. One could argue
    your plate is not calibrated, (if used) to a known standard, but if new
    then it should have a calibration sheet with it, though chinese sourced
    plates are looked askanced but for most of us they, or any used plate
    is more than adequate for the task, likely flatter than the milling table,
    the other option.
    Last edited by sch; 12-30-2011, 11:33 PM.
    Steve

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    • #3
      Dennis,

      I just recently got a surface plate and height gage. Today I am working on dialing in my new lathe chuck. I set up my test bar ( a 24"X1.25" Turned Ground and Polished bar) in two Vee blocks on the surface plate. I mounted a dial test indicator to my height gage and checked the test bar for straightness before mounting in in the new chuck. The bar turned out to be within .0007 over 20". Not bad to use in dialing in my new chuck. I also set the dti over the center of the bar then spun the bar. I had little to no run out.

      This was really the first opportunity I've had to use the surface plate.

      Tim

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      • #4
        One can, if interested, "calibrate", or at least "check" a plate for substantial errors.*

        You use another smaller plate, or any somewhat smaller item which "blues against" the plate in at least one position.

        if this smaller plate or item "blues against" the large plate in various locations and at right angles, or any arbitrary angle vs teh edges, you can make a pretty good case for the plate being 'good".

        barring a few really pathological cases (which Evan will likely bring up), this shows that the tested surfaces of the two items (plate and test piece) are "flat" (truly planar) within the ability of the spotting process you employed to determine.

        if the two items were made at different times in different places, the pathological cases drop to a much lower probability.

        * my experience is that the standard of even teh low cost chinese plates is pretty darn good, and you should pretty well be able to rely on them without listening too hard to those howling for 'calibration"..... The "calibration" might well cost much more than the plate, and it's theoretically "good" only for a year, although that is in reality a totally arbitrary time.
        Last edited by J Tiers; 12-31-2011, 12:13 AM.
        CNC machines only go through the motions

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        • #5
          Sadly, the most common use of mine is for a flat surface to back sandpaper.

          It's probably abuse of the block, but I don't need it as a calibrated flat surface for the stuff I make, and it was only $30 shipped.
          Hemi-proprietor,
          Esoteric Garage

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          • #6
            A granite plate, angle plate and a vernier or digital height gage lets one quickly and easily precisely layout hole patterns on metal surfaces covered w/ Dykem or other suitable dye. Carefully centerpunch the holes and you'll find you can get holes in position to .005 w/o going too nuts. For those of us w/o digital readouts on the mill, this is a big win.

            - Bart
            Bart Smaalders
            http://smaalders.net/barts

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            • #7
              Mine gets used off and on as a backer for sandpaper. Usually I've milled a surface, then want to keep it flat while sanding off the markings to the appropriate extent. I also have some 1 inch thick granite tile that I normally use for this purpose.

              I made a built-up assembly some time ago to give myself another dimension in tool bit holding on the lathe. This assembly was bolted and epoxied together, and I used the surface plate to align the pieces to each other while the epoxy cured.

              You can check a piece of shafting on a surface plate to see how out of straight it is, you can check the important edges on straight edges, squares, etc, and you can also check to see how square a square actually is. You will need two blocks for this, as you will first compare the blocks to each other to see if they are square.

              I bought a very sturdy wood lathe a while ago to convert into a combination high speed lathe/milling machine. The lathe has flat ways, and at one point I set the bed upside down on the surface plate to check for warp. I have also considered setting the surface plate upside down on the mill table to check it, but have not yet done this.
              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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              • #8
                Originally posted by barts
                A granite plate, angle plate and a vernier or digital height gage lets one quickly and easily precisely layout hole patterns on metal surfaces covered w/ Dykem or other suitable dye. Carefully centerpunch the holes and you'll find you can get holes in position to .005 w/o going too nuts. For those of us w/o digital readouts on the mill, this is a big win.

                - Bart
                good that you mention it. Had a visit from a nice young guy recently, new to the hobby and very CNC focused. Couldn't understand the value in a having a nice surface gauge or surface plate. I'm thinking how else to you hold a scriber or indicator? lol. Point is the best results come from pulling knowledge and skills from all eras and areas. While traditional layout maybe less used today, it still very useful even you you have all the bells and whistles

                Layout out like this can simply be the quickest way to get the job done: prick punch, centre punch, drill press can be the quickest way to get the job. Add in a dial height gauge and an optical centre punch and you better than .005" Throw in some good transfer punches and you're ploughing through big parts of a build without cranking a handle
                in Toronto Ontario - where are you?

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                • #9
                  Darryl,,,,, Re: "To convert into a high speed Lathe/milling machine" ???

                  Got any pics or descriptors of this project??

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