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  • Speed of Carriage Advance

    My lathe has a "Feed Rate Selector Lever" on the front of the headstock that lets me select the speed at which my carriage advances when I am turning a part. "A" has a value of 0.005", "B" has a value of 0.010", and "C" has a value of 0.0025".---There is absolutely nothing on the lathe nor in the Chinglish manual that tells what these numbers relate to. Is it carriage advance relative to headstock rotation? All I know is that when turning a piece, "A" is the mid range carriage advance speed and leaves a good finish on the part being turned. "B" moves the carriage twice as fast, but leaves a poor finish on the part being turned (looks like small thread pattern) and "C" is half of "A" speed which leaves a remarkably good finish on the part being turned but you could die of old age waiting for the cut to finish. I just leave this lever set on "A" all the time. Is it common to use all 3 different ranges when turning down a part.--for instance, using "B" for a roughing cut to quickly get down close to size, then "A" for getting even closer with a better finish, then using "C" for a final and really smooth finish on the part?---Brian Rupnow
    Brian Rupnow

  • #2
    Originally posted by brian Rupnow View Post
    My lathe has a "Feed Rate Selector Lever" on the front of the headstock that lets me select the speed at which my carriage advances when I am turning a part. "A" has a value of 0.005", "B" has a value of 0.010", and "C" has a value of 0.0025".---There is absolutely nothing on the lathe nor in the Chinglish manual that tells what these numbers relate to. Is it carriage advance relative to headstock rotation? All I know is that when turning a piece, "A" is the mid range carriage advance speed and leaves a good finish on the part being turned. "B" moves the carriage twice as fast, but leaves a poor finish on the part being turned (looks like small thread pattern) and "C" is half of "A" speed which leaves a remarkably good finish on the part being turned but you could die of old age waiting for the cut to finish. I just leave this lever set on "A" all the time. Is it common to use all 3 different ranges when turning down a part.--for instance, using "B" for a roughing cut to quickly get down close to size, then "A" for getting even closer with a better finish, then using "C" for a final and really smooth finish on the part?---Brian Rupnow
    Put a dial travel indicator against the carriage. With all the drive mechanics engaged, turn the headstock spindle one complete revolution by hand.
    I bet those values are feeds in "inches per revolution". but they could be something else. By doing the test yourself, You will know, and we won't need to guess.

    report back! ;-)

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    • #3
      Good call, CalM--I did exactly what you suggested and it turns out my guess was correct. Those markings do indicate travel per revolution of the headstock spindle. Now, the second part of my question--Do machinists commonly change these settings for roughing and finishing cuts or just leave it set at mid range as I do?
      Brian Rupnow

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      • #4
        Like a good guitarist who uses all the frets on the neck of his guitar a machinist sooner or later uses all the available speed/feed combinations on his machine tools.

        There are several variables to consider before applying the cutting edge to the material. Some variables have to do with material and its condition, others the cutting tool material and its configuration, still others with chip formation etc. Confusing at first but a little practice will lead you to judgement and confidence. Spend a little time experimenting with feeds speeds and tooling on surplus material before yu commit to expensive material and actual part production. You may have a few difficulties but they are part of the learning process - learn to walk before you run - learning is seldom noted for easy progress - pick your aphorism.

        Generally speaking, finer feeds are used for finishing cuts, stock removal on frail parts or for delicate cutting tools and coarser feeds for roughing and stock removal.

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        • #5
          Originally posted by brian Rupnow View Post
          Good call, CalM--I did exactly what you suggested and it turns out my guess was correct. Those markings do indicate travel per revolution of the headstock spindle. Now, the second part of my question--Do machinists commonly change these settings for roughing and finishing cuts or just leave it set at mid range as I do?
          Yes. Its common to use much higher feed rates while roughing. After a certain DOC its better to go faster feed then deeper cut to remove more metal per second.

          You might use the medium feed for finishing or getting things to size, then perhaps switch to your final feed if a good finish is required and do one final spring cut, or move the cross slide 0.001" in for your final pass. Maybe also increase the RPM for the final pass to speed it up some, as most tools can handle a little more SFM with very light cuts. (Especially carbide)
          Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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          • #6
            Brian I use a whole bunch of different feed rates when turning anywhere from .0004 to .038 per rev. . If you want a finer feed look at your QCGB and pick the finest thread there is .

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            • #7
              The .0025 in/rev feedrate equates to 400 threads per inch. His QCGB is pretty unlikely to have a finer thread on it that that, but of course I could be surprised.
              .
              "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

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              • #8
                Also if you're swarf comes off in long strings you can generally increase the feed rate until it starts making chips.

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                • #9
                  " "B" moves the carriage twice as fast, but leaves a poor finish on the part being turned (looks like small thread pattern) "
                  Increase the tool engagement. That can mean deflection and rigidity issues.
                  There's a rule of thumb something like radius is twice the IPR.
                  Forrest , speak up, I'm past the 24th fret.

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                  • #10
                    It isn't a speed, it is a rate and it is travel distance/one turn of the spindle. Not obvious is what it means regards doc and finish, and rate of material removal, and each of these involves the cutter form.

                    A sharp V shaped cutter will leave a spiral at 0.005"/turn where a rounded nose cutter will leave a mirror finish. At a greater feed rate even a rounded nose cutter will leave a spiral. These feeds are used for metal removal vs threading, and the efficiency/expediency depends on the cutter form factor. The combination of feed rate, doc, and cutter geometry produces a sweet spot of removal rate or last pass finish. Finding that sweet spot is what makes this an art form. You can burn up a lot of hours at 0.005"/turn and get a beautiful finish with each pass, but that is clearly not efficient. On the other hand some metals like 1018 will smear at 0.005"/turn but shine like a mirror with slower deeper cuts. Then add in the effects of HSS vs carbide, rake angle, doc and height of the cutter relative to the center line of travel and you realize with old timers know by rote. It all doesn't come from a book, some, the majority, comes from watching what your setup and material are producing vs what you expect.

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