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Hard turning vs grinding

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  • #16
    Thanks again. It sounds like something I'd like to try and do.

    Would some trash-bag plastic and duct tape work to contain dust?

    Are the wheels [url=http://www.mcmaster.com/#grinding-wheels/=2o9gv2]here[/url the correct type?

    For my 9" lathe is the 3" size right?

    Gary

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    • #17
      Yeah...if you have a toolpost grinder and want to try it on your lathe, be really anal about covering everything. Even then, you should figure on wiping all way surfaces with kerosene after "untarping" it and then drying them and re-lubricating. Wheel grit mixed with oil=lapping compound.

      Just to correct something you said.....wheels that produce a fine surface finish are not necessarily "fine". Certainly finer wheels often result in a finer surface finish, but overdo it and you end up with a wheel loaded with metal particles which then result in a "galled" surface and a real mess. This is likely more esoteric than you want to get right now, but as a previous poster mentioned, often an open, friable wheel is the right answer so that the wheel does not load up. There are all sorts of "grades" of hardness and openness of the wheel material in addition to grit size to consider. Think of grinding as it's own class of machining....with its own set of stuff to learn. In any case, a "fine" wheel may still be 80 grit with 60 much more common and 46 often used and still producing surfaces with a better surface finish than milling will typically do.

      Paul
      Paul Carpenter
      Mapleton, IL

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      • #18
        Grinding IS it's own class of machining called abrasive machining. There are just as many improvements in abrasive machining in recent years as there have been in cutting tools that make hard turning practical. Modern super-abrasives make possible grinding operations that were impossible just a few years ago. Using CBN wheels in profile configuration very little wear occurs to the wheel and it maintains it's shape for a long time. Almost no grit from the wheel is released to contaminate the work area.

        Anothe recent technique is "creep feed grinding" where very deep cuts are taken at low advance rates. This is also only possible with wheels that don't wear quickly.

        Here is an example of creep feed grinding where I made a form tool for milling plastic parts. The tool is ground to profile with a copy attachment and the wheel is fed to full depth of cut in a single pass. It is an 8 inch CBN (Cubic Boron Nitride) wheel and doesn't require dressing.

        First the edge profile is ground and then the clearance and rake angles are ground, each in just a single pass.

        [edit] The material being ground is High Speed Steel.



        Last edited by Evan; 07-09-2009, 07:10 PM.
        Free software for calculating bolt circles and similar: Click Here

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        • #19
          Originally posted by Evan
          Here is an example of creep feed grinding where I made a form tool for milling plastic parts. The tool is ground to profile with a copy attachment and the wheel is fed to full depth of cut in a single pass. It is an 8 inch CBN (Cubic Boron Nitride) wheel and doesn't require dressing.
          Evan,

          How is the blade attached?

          Gary

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          • #20
            The last time I posted this I caught a bunch of flack because it was supposed by some that every newbie to machining was going to make something like this and try to machine a log of 4140 with a three inch wide form tool.

            I don't make the assumption in my posts the the people reading this are stupid. I have yet to meet a stupid machinist although some can be ignorant at times.

            Anyway, don't try this at home folks unless your equipment can handle the load with all variables considered.

            The part design was slightly modified to accommodate the change to Delrin.



            Free software for calculating bolt circles and similar: Click Here

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            • #21
              Very neat!

              Is that a horizontal mill?

              Gary

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              • #22
                Yes it is. You can read all about here:

                http://bbs.homeshopmachinist.net/showthread.php?t=25928
                Free software for calculating bolt circles and similar: Click Here

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