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  • Unwanted taper

    My lathe is cutting an unwanted taper. A little backround first, it's a Craftsman/Atlas 12x36 I just bought. It has 1/2" thick flat ways that have .002" wear on the outboard way for about the first 8" from the head stock, everywhere else measures spot on. I don't have a machinists level, so I got it close with a regular one and used "Rollies Dads Method" http://igor.chudov.com/manuals/Rolli...-Alignment.pdf
    to align the lathe. Please advise me if I did this correctly, I chucked up a steel bar 16" long with the same dimension through out, mounted a dial indicator in the tool post made sure it was on center and found the high and low spots next to the chuck. I then zeroed the DI on the average. I moved the carriage to the end of the bar and found the average of the high and low and compared that to zero. The difference was .007, I then shimmed under the rear of the lathe at the HS end till the two averages met. I then repeated the whole process and found a difference of .001, I shimmed again until they matched. Now it is still cutting a taper of about .003 in just 2". My test piece is aluminum 2" in diameter, I am taking .005 cuts and it measures smaller next to the chuck. There is no provision to adjust the headstock as it fits snugly between the ways. Any advice?

    Stu
    Last edited by Stu; 03-03-2015, 06:59 PM.

  • #2
    I'm not sure if you are turning between centers or not. If so, most lathes let you adjust the tailstock and it sounds like the tailstock needs to move towards you just a tad.

    If you aren't turning between centers, then my input probably won't be that useful.

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    • #3
      I'm no turning between centers, the test piece is 4" long

      Bill

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      • #4
        LH/RH shimming sounds off whack somehow, ie front and back as it sounds like a sort of twist thing, does that make any sense, I've only ever done a small myford so experience limited, you clocked horizontally but how's axialy, ie 12 o clock and 3 o clock?
        If 3 o clock is out then as has been said your tailstock is offset by a few thou
        Turn a collar both ends the same, set the crosslide to zero, measure the diameters and move the tail til they match
        Mark
        Last edited by boslab; 03-03-2015, 06:28 PM.

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        • #5
          That sounds correct to me, I think. Just to clarify: you got the indicator to center its movement on zero up near the headstock, for example in one revolution of the test bar the indicator needle might go -3, +3.
          You then moved the indicator out to the end of the bar, but did not touch its adjustment. At the end of the bar, the reading range might be +1, +7. By shimming one leg of the lathe, and only by shimming the leg of the lathe, without touching the indicator, you got the indicator to read -3, +3 in one revolution of the test bar.

          Is that what you did?
          ----------
          Try to make a living, not a killing. -- Utah Phillips
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          • #6
            Originally posted by SGW View Post
            That sounds correct to me, I think. Just to clarify: you got the indicator to center its movement on zero up near the headstock, for example in one revolution of the test bar the indicator needle might go -3, +3.
            You then moved the indicator out to the end of the bar, but did not touch its adjustment. At the end of the bar, the reading range might be +1, +7. By shimming one leg of the lathe, and only by shimming the leg of the lathe, without touching the indicator, you got the indicator to read -3, +3 in one revolution of the test bar.

            Is that what you did?
            Yes, exactly

            Stu

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            • #7
              Did you measure the diameters at both ends of the bar?

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              • #8
                Originally posted by Forestgnome View Post
                Did you measure the diameters at both ends of the bar?
                Yes, both ends are the same diameter.

                Stu

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                • #9
                  I suspect headstock alignment is off a bit. Often there is enough clearance to rotate it slightly.
                  Don Young

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                  • #10
                    I've also got a Craftsman 12 x 36 and did Rollie's method first. I still felt like it wasn't quite right so used a level and it showed I should do some additional (or different) twist adjustment. Adjusting it vial the (precision) level seemed to fix it up. I've never quite understood it because in theory the Rollie method should be fine, but this was just my experience.
                    .
                    "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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                    • #11
                      Originally posted by Stu View Post
                      Yes, both ends are the same diameter...
                      If the piece is the same dimension on both ends there is no taper--sounds like you've got it dead nuts...
                      Keith
                      __________________________
                      Just one project too many--that's what finally got him...

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                      • #12
                        I see two scenarios possible here- one is to chuck a fairly large diameter test piece and take light finishing cuts with a sharp tool- the other is to use a small diameter test piece with a tool that may not be sharp, or ground with proper relief angles. It's very easy to deflect a work piece at the unsupported end, thus leaving that end large compared to a spot closer to the chuck jaws. You do need to know if this is happening (and it's a fairly common thing).

                        As soon as you start using a tailstock center things will change, and it's not always obvious what is happening when measurements show inconsistencies.
                        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                        • #13
                          You shouldn't be expecting much better with 4 inches sticking out of the chuck and no tailstock support. Drill the end and install a center and the taper will possibly go away.
                          A chuck with worn jaws will allow a little flex of the work away from the cutter. Up next to the chuck you should not see it.

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                          • #14
                            Originally posted by Gary Paine View Post
                            You shouldn't be expecting much better with 4 inches sticking out of the chuck and no tailstock support. Drill the end and install a center and the taper will possibly go away.
                            A chuck with worn jaws will allow a little flex of the work away from the cutter. Up next to the chuck you should not see it.
                            The chuck does have some bell mouthing on the jaws, I'll check that out, Thanks

                            Bill

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                            • #15
                              Originally posted by darryl View Post
                              I see two scenarios possible here- one is to chuck a fairly large diameter test piece and take light finishing cuts with a sharp tool- the other is to use a small diameter test piece with a tool that may not be sharp, or ground with proper relief angles. It's very easy to deflect a work piece at the unsupported end, thus leaving that end large compared to a spot closer to the chuck jaws. You do need to know if this is happening (and it's a fairly common thing).

                              As soon as you start using a tailstock center things will change, and it's not always obvious what is happening when measurements show inconsistencies.
                              Good points, I'll try that. Thanks

                              Bill

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