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dead centers are almostst worthless, why buy them.

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  • dead centers are almostst worthless, why buy them.

    when I need a center it is on a long slender workpiece and I never turn slow.

    I am buying a new machine and it comes with dead a dead center, after 14 years machining and have naver used a dead center and have burnt up old shop live centers.

    I guess i will machine the dead center for a bearing and turn it into a bull nose and it wont be junk then.

    [This message has been edited by tattoomike68 (edited 04-21-2005).]

  • #2
    Ever used a faceplate and a dog to turn a shaft? You may want to hang onto it but a bullnose is good too.
    Non, je ne regrette rien.

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    • #3
      Well, to each their own.

      Never seen a "half" live center, but they might exist...like "CNC" centers, sort of.

      Dead centers can't rattle, live ones can. Might make a difference when grinding things...

      I don't use them much, but when I do its for a reason.....might be a bad reason, but it works.
      1601

      Keep eye on ball.
      Hashim Khan

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      • #4
        Dead center is way better when you're down to the last few tenths (bearing fits, toolpost grinding, etc.)

        The best live centers on the planet have measureable play, although that play is often less than 0.001". General purpose home shop live centers have more.

        For general turning, profiling and threading they work well. For critical work that has to be dead nuts, the dead center is easier.

        ------------------
        Barry Milton
        Barry Milton

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        • #5
          I don't use one too often,but there are times.

          Like turning between centers and starting taps,reamers and other non-piloted tools..
          I just need one more tool,just one!

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          • #6
            I always use a dead center, when turning work between centers. One has to pay attention and back it off as the work heats up, and keep it lubricated, but I don't find that it's all that big a deal.
            ----------
            Try to make a living, not a killing. -- Utah Phillips
            Don't believe everything you know. -- Bumper sticker
            Everybody is ignorant, only on different subjects. -- Will Rogers
            There are lots of people who mistake their imagination for their memory. - Josh Billings
            Law of Logical Argument - Anything is possible if you don't know what you are talking about.
            Don't own anything you have to feed or paint. - Hood River Blackie

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            • #7
              Use them a lot for threading between centers.Also half centers.

              Comment


              • #8
                <font face="Verdana, Arial" size="2">Originally posted by precisionworks:
                Dead center is way better when you're down to the last few tenths (bearing fits, toolpost grinding, etc.)

                The best live centers on the planet have measureable play, although that play is often less than 0.001". General purpose home shop live centers have more.

                For general turning, profiling and threading they work well. For critical work that has to be dead nuts, the dead center is easier.

                </font>

                Barry -
                Yours is one opinion here that I particularly value. As a curious rookie, I have a question, though.

                Machinist types, by and large, are a pretty damn clever bunch, and like so many things, the more I learn about this stuff, the more I find that I don't know, and the more I find that smart people have done just about all of it before I considered any of it. Having said that...

                You said that *every* live center has detectable play. Isn't it possible to create a live center with tapered contact surfaces so that wear can be compensated for by a bit of "preload"?

                Imagine a live center with the moving part shaped like 2 cones back to back. One cone is the normal pointy bit that contacts the work, and the other mates to a conical "socket" in the static part of the tool. Put roller bearings between the static and the moving surface. Couldn't this arrangement be free of play, provided there is a little "preload" pushing the live center into the work? Yeah, I know the roller bearings would also have to be conical, because the different diameter parts of the cone have different linear speed.

                I understand that this is a rookie question, but is it easy to explain why this wouldn't work, or hasn't been tried? Thanks.

                -M
                The curse of having precise measuring tools is being able to actually see how imperfect everything is.

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                • #9
                  Wirecutter,

                  Unless you're doing really close-tolerance work a live center will provide adequate support. The very finest ones (Ritten, Royal, Nakane) guarantee TIR of .0002" (+/- .0001). Even in the home shop sizes of 2MT or 3MT the prices run around $200 to $300.

                  Their design is really close to what you described, including adjustment for bearing preload. Here's an internal photo from Nakane

                  One potential problem with any center, live or dead, is thermal expansion and workpiece distortion. The close-tolerance live centers add expansion compensation features, usually with a sliding fit mechanism. That way the center maintains constant contact pressure on the workpiece.

                  On jobs where there's little tolerance like +/- .0001, I use the dead center. For everything else the live center works great.

                  ------------------
                  Barry Milton
                  Barry Milton

                  Comment


                  • #10
                    <font face="Verdana, Arial" size="2">Originally posted by precisionworks:


                    The best live centers on the planet have measureable play
                    </font>
                    Now Barry...Here's a secret...(my wife picked this up from a hairdresser at the Bingo Hall)
                    Add another handle to the tailwheel. Put a 5 foot long bar(preferably metric) through the two handles. Lift up on bar and spin tail wheel around until it puts at least 600 foot pounds of pressure on the live center. This will all but eliminate any play from the live center!
                    You'll know you've over tightened it if the chuck and spindle push through the rear of the lathe and fall on the floor!
                    Glad I could help!

                    I have tools I don't even know I own...

                    Comment


                    • #11
                      <font face="Verdana, Arial" size="2">Originally posted by chief:
                      Ever used a faceplate and a dog to turn a shaft?</font>
                      I've reported you to the Animal rights Group.

                      Comment


                      • #12

                        Hmmm. I think I like Torker's answer. Ya shoulda heard the answers I got when trying to figure out what "lathe dogs" were for... Well, a little RTFM cleared that little mystery up...

                        Barry -
                        Thanks for that - great pic, too. I just knew there was a good explaination - and didn't think enough about just how sensitive things get down at .0001".

                        -Mark
                        The curse of having precise measuring tools is being able to actually see how imperfect everything is.

                        Comment


                        • #13
                          Thermal expansion,one more reason for flood coolant.
                          Got to keep those big parts cool otherwise they will expand and load both the live center bearings and the headstock spindle bearings.

                          Something to consider next time you turn a 3' long piece of 2" shafting.
                          I just need one more tool,just one!

                          Comment


                          • #14
                            I use my live centre all the time. I usually don't bother with the dead centre I have...I thought it was useless until the day came I had to turn a long shaft....As soon as I got a third of the way along the shaft chronic chatter set in....I did everything including praying to the great Master Builder in the sky but nothing stopped it...Until I used the dead centre...All the chatter stopped...And this was a fairly good quality live centre I have...
                            Precision takes time.

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                            • #15
                              Okay, I'm with you guys.

                              Took my live center out to the back yard and shot it dead. Now, after all that misery, life is good

                              Actually I do have a question relating to my live center while it was alive. It did not turn freely so I rarely used it. Is there some way to clean/lubricate them or are they factory sealed and tossed when they no longer turn freely?

                              [This message has been edited by Your Old Dog (edited 04-22-2005).]
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                              It is true, there is nothing free about freedom, don't be so quick to give it away.

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