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get the spring out

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  • get the spring out

    Yesterday I was boring out a piece of 3/4" thick aluminum plate, 3" ID, grade unknown, and when I was about .050" under size I made a couple of cuts with out moving the cross slide to turn the "spring out" so I could get an accurate measurement before making my final assault on the finish dia. Now after about 5 or 6 cuts with the same settings I'm still getting a little swarf coming off, not much maybe a fraction of a thou. This was with a 3/4" dia boring bar with HSS tool.

    At what point is it finished, It seems like it should reach a point where the tool doesn't cut anymore, can anybody explain this to me.
    The shortest distance between two points is a circle of infinite diameter.

    Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

  • #2
    Fine Cut

    Dull Tool. Use diamond wheel to obtain a SHARP cutting edge.

    JRW

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    • #3
      Play in the crosslide, etc. On my lathe, the parts like to rest away from the spindle axis, so if I dial in to make a cut, the tool generally doesn't creep toward the workpiece. But boring is the opposite- the play still wants to come out of the slides the same way, but it puts the tool towards the work instead of away from it. I can take a boring cut, move the carriage away then bring it back right away for another cut at the same setting and it will be fine (taking a much lighter skim cut) but if I move the carriage away then wait several seconds or more before taking the skim cut, more material comes off.

      Of course, boring is a process where flex in the tooling is always present. I find that it's a careful balance of angles ground into the tool to enable a cut to be made that allows the boring bar to remain in exact position, neither flexing towards the work (digging in) or away from it. If it digs in, a subsequent cut may have the tool not taking a skim at all, and if it pushes away then subsequent cuts keep taking off material- that or the tool just rubs. It seems that the height of the tool is more critical when boring as well.
      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
        Depending on the geometry of your piece, and how fast you bored the basic dimension, the 'hole' could be contracting as it cools to room temp. This is especially evident when the hole is large relative to the OD. The use of coolant or waiting for the part to cool to room temp before finishing will make a difference.

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        • #5
          OK, thanks guys.
          The shortest distance between two points is a circle of infinite diameter.

          Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

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          • #6
            When I'm working on aluminum it heats up while taking multiple passes. I take my very last cuts after its set awhile and reached room temperature to avoid temperature expansion problems. It works for me.
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