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6 micro inch surface finish - hard or not?

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  • 6 micro inch surface finish - hard or not?

    I need to make a stainless steel piece that has a 6 micro inch finish inside a 3/4" hole. (The symbol looks like the 6th root of "polish".) I am wondering if this spec is hard to meet or not. One chart I saw calls it 500 grit, and at the same time calls it "mirror finish". Now I know that 500 grit does not leave a "mirror finish" as I can still see haze and scratches. What grit sandpaper or other polishing techniques would I need to be able to reach this spec? I saw a thread where old tiffie tried to post some pictures, and the 6 micro inch panel still looked like it has some fine scratches. The workpiece is a cylinder, so I am free to run sandpaper, hones, reamers, laps, etc thru the hole.

  • #2
    That sounds pretty easy. The question is, is it ok to exceed the spec?
    Free software for calculating bolt circles and similar: Click Here

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    • #3
      You would normally continue on using finer and finer grit, finishing up with a polishing compound to get something like a mirror finish, but as Evan has pointed out, you might be needing to stay to a spec-
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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      • #4
        You at least need one of these guys.

        http://www.ebay.com/itm/Surface-Roug...item43b831ab4e

        A 6 is pretty spiffy looking. Not the easiest thing to get with just cutting tools, easier on some materials than others. All depends on how your customer is
        going to measure it. If "shiny enough" is the criteria for acceptance, then just make her shiny.

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        • #5
          Can't comment for over the pond drawings, but here the surface markings on a drawing mean "this or better", unless otherwise noted.
          Amount of experience is in direct proportion to the value of broken equipment.

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          • #6
            Originally posted by Jaakko Fagerlund View Post
            Can't comment for over the pond drawings, but here the surface markings on a drawing mean "this or better", unless otherwise noted.
            That is true here also, and should be universal.

            The issue is what OTHER requirements exist..... size tolerance, cylindricity, straightness, etc. Getting a polish is one thing, getting it on a surface that is the right size and conforms to the various geometry requirements may be another.
            1601

            Keep eye on ball.
            Hashim Khan

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            • #7
              Originally posted by beanbag View Post
              One chart I saw calls it 500 grit, and at the same time calls it "mirror finish". Now I know that 500 grit does not leave a "mirror finish" as I can still see haze and scratches. What grit sandpaper or other polishing techniques would I need
              that is a good question. 500 grit emery paper is hardly going to leave a mirror finish as you point out. Yet lapping with 600 grit compound, while not a perfect mirror, certainly starts to become reflective...where's I can get incredible finishes on a grinder with 60 grit. I'd think the 'grit' scale is the same in each instance, but clearly depending on the technique used very different finishes can be produced
              .

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              • #8
                Before I retired I spent a lot of time grinding high speed steel and carbide cold former dies. They needed to have mirror finishes to keep the piece part from sticking to the ID of the die.

                My procedure was to grind the ID as smooth as possible then polish it with a pencil grinder with a felt bob in it and diamond lapping compound. With the part running the reverse direction of the pencil grinder and at full speed I could polish them to a mirror finish in about 5 to 10 minutes. Sizes were about 1/2 to 1 inch dia. and 2 to 3 inches deep.

                We had a profilometer and the best finish that I ever achieved IIRC was about a 3 microfinish. Shiny as a mirror.

                Brian
                OPEN EYES, OPEN EARS, OPEN MIND

                THINK HARDER

                BETTER TO HAVE TOOLS YOU DON'T NEED THAN TO NEED TOOLS YOU DON'T HAVE

                MY NAME IS BRIAN AND I AM A TOOLOHOLIC

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                • #9
                  Originally posted by bborr01 View Post
                  Before I retired I spent a lot of time grinding high speed steel and carbide cold former dies. They needed to have mirror finishes to keep the piece part from sticking to the ID of the die.

                  My procedure was to grind the ID as smooth as possible then polish it with a pencil grinder with a felt bob in it and diamond lapping compound. With the part running the reverse direction of the pencil grinder and at full speed I could polish them to a mirror finish in about 5 to 10 minutes. Sizes were about 1/2 to 1 inch dia. and 2 to 3 inches deep.

                  We had a profilometer and the best finish that I ever achieved IIRC was about a 3 microfinish. Shiny as a mirror.

                  Brian
                  Hi Brian,

                  WOW!!

                  Did you ever investigate dimensional or geometry changes from finish grind to final polish?

                  Dave

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                  • #10
                    I'll stand-in for oldtiffie till he pitch up.

                    http://www.roymech.co.uk/Useful_Tabl...in_Values.html

                    Phil

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                    • #11
                      You pretty much have to grind to obtain that level of finish.Anyboby know what finish is specified for hydraulic valve lifters? They would seem to me to be that level. Bob.

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                      • #12
                        Two things I have noticed about using sandpaper for surface finish. First, higher speed works better. I generally work at 2-4 times the speed you would use for a HSS cutting tool. Second, a bit of oil or cutting fluid on the sandpaper will very noticeably improve the surface finish.

                        Keeping the flatness or other figure of the surface under control when using sandpaper can be problematic. I am not familiar with working in a hole, but using sandpaper on an OD next to a shoulder can be difficult to control. The diameter reduction near that shoulder will be less than at a distance from it.

                        I keep an assortment of sandpaper up to 2000 grit. It is fairly easy to get a mirror finish with 2000 grit plus oil, using a high speed. But, of course, you must use all the lower grit grades in succession first.
                        Paul A.
                        SE Texas

                        Make it fit.
                        You can't win and there is a penalty for trying!

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                        • #13
                          I am not familiar with working in a hole
                          Rule one: Don't stick your finger in there unless it smells like fish.
                          Free software for calculating bolt circles and similar: Click Here

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                          • #14
                            Originally posted by Evan View Post
                            Rule one: Don't stick your finger in there unless it smells like fish.
                            Rule two: Don't stick your dick in a fish.
                            Amount of experience is in direct proportion to the value of broken equipment.

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