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Another Diamond Paste Question: How Much Removal To Expect

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  • Another Diamond Paste Question: How Much Removal To Expect

    I have heard that diamond laps can work fast. But just how fast is fast? Assuming cast iron and, perhaps a 40 micron diamond paste for starters, just how much material can I expect to remove with a reasonable amount of lapping time?

    I have some 1-2-3 blocks that developed a bit of rust. I have cleaned them, but I know they are a bit oversized, 0.001" or less, and I am thinking about lapping them with aluminum foil on a surface plate and diamond paste. To remove a few tenths from each side, am I looking at a few dozen strokes, a few hundred, or thousands?
    Paul A.
    SE Texas

    And if you look REAL close at an analog signal,
    You will find that it has discrete steps.

  • #2
    Hi,

    Ain't no way to give a solid answer. It depends on just how coarse the grit, how much of it, how hard the to be lapped part is, how hard you press, to how long each stroke is.
    If you think you understand what is going on, you haven't been paying attention.

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    • #3
      With 40 micron paste youll be at it a while to get much of anything removed. That grade is roughly equilavent to a 4-600 grit sandpaper. Now, diamond does cut quicker and last than your average sandpaper, but still, itll take a while to remove much. A single thou would probably be accomplished within a reasonable amount of time though

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      • #4
        I used diamond paste to "wring" the piston into the cylinder of my two stroke marine engine I built. It was a ported engine, so I couldn't have rings on the piston, but I wanted a really close fit. It worked quicker than aluminum oxide based paste, but not a lot quicker.--And it was a real bugger to "seize". I spent as much time running out to my arbor press to unstick the piston as I did making it fit. I don't remember what grade of diamond paste I used. EDIT EDIT--I just found the thread about building my 2 cycle engine, and although "diamond lapping paste" is mentioned half a dozen times, I never actually wrote what "grade" it was.
        Last edited by brian Rupnow; 06-02-2018, 07:35 PM.
        Brian Rupnow
        Design engineer
        Barrie, Ontario, Canada

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        • #5
          Originally posted by Paul Alciatore View Post
          I have some 1-2-3 blocks that developed a bit of rust. I have cleaned them, but I know they are a bit oversized, 0.001" or less, and I am thinking about lapping them with aluminum foil on a surface plate and diamond paste.
          I think it will go well. You are not trying to shape the block, just polish them right?

          Because all that grade will do is polish. If you have a bumpy surface the high spots will get polished, and so on down the line to the surface finish you start with.

          Why are the bloxs oversized? I dont understand. Are they shop made blocks? JR

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          • #6
            so you want to remove lets say 3 tenths = 0.0076 mm using 0.04 mm grit? much to coarse imo. 40 micron is fepa p360 grit and about 300 cami.

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            • #7
              No I am not trying to shape the blocks, just trying to clean them up a bit more.

              Why oversized? No they are not shop made, but they are imports. I read somewhere, perhaps on this board, that sometimes the 1-2-3s are deliberately made a few tenths oversized to allow the purchaser to dust them down to the final dimensions. But perhaps that is not correct. I also remember measuring them when I got them and I recall that they were a bit oversized. But that was not with my present instruments. At that time I had a 0-1" Vernier micrometer (tenths) and my best calipers at that time were German made Vernier style. And no Jo blocks to check them against. So, those measurements were not the best.

              I spent some time just now with the block that I have cleaned the best and with a better collection of micrometers that span up to 3". And I now have a set of shop blocks to check them against at both ends of their range. Here is what I found:

              1" dimension: 0" to +0.0001" (using Fowler digital mike, checked at zero and 1" against 1" shop block)

              2" dimension: -0.0002" to 0" (using Craftsman metric mike, checked at 1" and 2" against shop blocks)

              3" dimension: -0.0005" to -0.0005" (using 2-3" micrometer with 0.0005" divisions, checked against 2" and 3" shop blocks)

              So it appears that the 1" dimension is a bit oversized while the 2" and 3" ones are dead on to a few tenths under. That -0.0005" point was one, isolated place: the other 3" readings are no more than -0.0002". It may be due to the rust that I cleaned off.

              So it appears that I really do not want to remove much at all. Worst case would be the +0.0001" on the 1" dimension. And again, that represents a couple of high points, not the general readings which were +0.00005" or less. So I would really just be trying to flatten them a bit better. I don't know if that will work or not, but with the rust damage to them, I don't feel I have a lot to lose. And I need some practical experience with lapping.



              Originally posted by JRouche View Post
              I think it will go well. You are not trying to shape the block, just polish them right?

              Because all that grade will do is polish. If you have a bumpy surface the high spots will get polished, and so on down the line to the surface finish you start with.

              Why are the bloxs oversized? I dont understand. Are they shop made blocks? JR
              Paul A.
              SE Texas

              And if you look REAL close at an analog signal,
              You will find that it has discrete steps.

              Comment

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