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Forrest

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  • Forrest

    I know there was a posting concerning this, but I want to hear it from the horses mouth Now first off I'm not calling you a horse!!!!
    Anyhow, I have been surface grinding some parts on my Cinci #2 t&c grinder, and it has been doing a good job for what I want. Now the question is, what is an acceptable depth of grinding to stay in the safe zone?
    Thanks,
    Jim
    Jim

  • #2
    Somewhere there's a front part of a horse that will make me complete.

    An acceptable depth for what?

    If you're referring to the way bearings of your #2 mill's it's to barely clean them up while retoring the part's features to linearity, plane, and geometry with its mating parts.

    There's no reason why machine tool parts can't be surface ground with good success and accuracy - and far more economically too for that matter. In fact a good hand running a side by side comparison of two rebuilt machine tools one surface ground and the other scraped would be hard pressed to find objective negative points with the ground Vs the scraped.

    The difference is in my thinking that you can't just run the parts willy-nilly through the grinding process and expect good results. Cast iron has to be ground with a clean sharp freshly dressed wheel - moreover the diamond dresser has to be sharp as well so it doesn't crush off the surface of the wheel but knocks out those individual that prodrude.

    Also there's distortion control. Long slender tables and hollow saddles will warp under grinding because of the flash temperatures inherent in the process. This warpage doesn't matter in in the usual run of steel parts but in a moving machine table it's of vital concern. As soon as the thin stressed film of surface ground metal wears in service the table will relax into a new configuration - perhaps one that adversely affects the machine's performance.

    For this reason exctruciating care must be taken by the grinder hand that the wheel's dress and the spark-out, ample coolant flow, the diminishing depth of cut as clean-up is approached, and the rest of the grinding variables are controlled in a manner that ensures an accurate, stress-free part is delivered to the rebuilder.

    The dovetail surfaces are very difficult to do on a surface grinder because the work has to be built up on a tilt and each DT's ground one at a time with a dish shaped wheel. A separate grinding spindle mounted on a swivel bracket on surface grinder's wheel head is something you frequently find in a machine tool rebuild shop. Way grinding machines build for the service may have as many as 4 wheel heads. I drew up mods to convert a 6 f x 6 ft x 20 ft Gray planer into a way grinding machine using a new Cadillac's worth of Pope motorized grinding spindles.

    Naturally anything FME sensitive as machine tool castings exposed to surface grinding swarf and dressed-off abrasive should be thoroughly pressure washed.

    One of the significant advantages of hand scraping is its a low energy method where the swarf and debris can be vaccummed up as they're generated; thus there's no need for complete dissassembly of an entire machime for a mere re-scrape.

    So, go ahead and grind your #2 Cincinnatti's parts. So long as you exercise care and caution and have a regard for cleanliness you'll be very satisifed with the results.

    [This message has been edited by Forrest Addy (edited 01-20-2005).]

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    • #3
      <font face="Verdana, Arial" size="2">Originally posted by shaque:
      what is an acceptable depth of grinding to stay in the safe zone?
      Thanks,
      Jim
      </font>
      Depending on the width of your wheel, .00025 (Quarter of a tho) or 2.5 ticks on height wheel should be safe depth. If your grinding a long piece, grind it at a 45 deg angle to avoid excessive heat buildup.

      If you hear the RPM drop while grinding, ease up on the depth until you can't hear the RPM drop.. That's usually the sweet spot.

      -3Ph

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      • #4
        thanks for the replies fellas. Yeah 3ph, that was what I was looking for, the safe amount to down feed.
        Jim

        Forrest:
        I did a part that I wasn't too fussy about, just a cleanup of milling marks, then for the fun of it, I measured it all around,when I was done, and it was smack on. Needless to say I am pleased.
        JS

        [This message has been edited by shaque (edited 01-20-2005).]
        Jim

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        • #5
          For what it's worth on suface grinding I take .001" DOC per pass and 1 turn of the crossfeed (.100") per traverse of the table for roughing. Then .0005 DOC and .050" crossfeed, Then .00025" DOC and still .050" crossfeed. If I'm ambitious I might drop to .025" crossfeed. Then a few sparkout (no downfeed) passes. I don't have coolant so I have to take frequent breaks to let the part cool down. Bad things hapeen when the part swells

          If it's not too big of a job, I enjoy running a manual surface grinder. Kinda of a Zen exercise.

          Using a T&C grinder, you might have to experiment. Proof is in the finish and how flat the part is.

          Enjoy Jon
          Jon Bohlander
          My PM Blog

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          • #6
            If I remember correctly, the depth of feed should not exceed 10% of the grain diamter of the grinding wheel being used. That was in '75, and I have not seen those notes in years nor used a surface grinder since than. We were taught to calculate the maximum depth based on the grit of the wheel. This was before creep grinding became common on surface grinders. Most small surface grinders suitable for home shops are not rigid enough for creep feed, which takes a deep cut at a slower feed rate than a standard surface grinder.
            North Central Arkansas

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            • #7
              Dang! I hate it when I do that; fly off on a tangent. I thought Shaque was concerned with how much stock to take off when grinding the way surfaces of cast iron machine tool castings. Sorry.

              OK: downfeed is the question. It depends on stock removal, the wheel, coolant, dress, and how that particular hunk of cast iron wants to grind.

              If you're grinding a thick piece for stock removal on a honkin big 30 HP Mattison die block grinder with a 24" wheel take a thou or more per cut. If you're running a 3 HP Abrasive or B&S a couple tenths is about it.

              The thing to remember is that cast iron can warp like crazy thanks to thermal shock from vigorous grinding and the work affected zone (not exactly work hardening but similar) from grinding with a dull wheel. Therefore in sensitive and long slender work the last three thousandths should be taken with due care with a sharp wheel and moderate stock removal.

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