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  • Custom Back Plate Material

    I am considering getting the 6" Southbend Set-tru chuck that Grizzly is offering in their catalog for my 10x22 lathe. I've been making some parts lately that are repetitive and need the best possible runout reduction. The 4 jaw satisfies the later but I hate having to fiddle again with each new part. They are all the same diameter but even if you only loosen two jaws and then clamp again with those jaws I still have to clock it back in again. Also the 4 jaw seems to suffer from some conical run-out in the jaws that I have not been able to remove so it kills me on working the ends of long shafts.

    Anyway, there is NOWHERE that I can find that sells partial machined plates for the 1-3/4" - 8 thread on the spindle nose. Nobody around here sells cast iron that I can find in the rough. My choices are to start with a 2" thick round of 6.5" 6061 that I can obtain locally, or perhaps the same in steel. The chuck is 6.5" in diameter and I can't seem to locate a place that can get me steel in that thickness and diameter. How bad would a 6061 plate be? My fear with AL is that the register boss would not put up with set screws mashing it and would get torn up.

    Shipping a hunk of steel that size is just stupid in price and 7075 AL is really pricey to start with. This off-size spindle thread is a real balls-ache when it comes to this but I hear lots of people love their set-tru 3 jaws and I would love to be able to put that baby on my lathe since my CDCO 5C chuck turned out to be a serious disappointment.

    Will 6061 be alright, would 7075 be a great improvement or would steel be the only natural choice? I'd rather not work cast iron really. Hate that grey grit going everywhere.

  • #2
    Photoman,

    What is your brand/model lathe that it has this nose thread?
    regards

    3t

    Comment


    • #3
      Lathe Chuck

      The 6061 would work, but I would go with 2024. It has a lot better tensile strength than 6061, but not the high cost of 7075. I would make shallow counterbores for the adjusting screws so as to not raise a burr that would interfere with adjustment. You also might want to consider a 6 jaw adjust true chuck too. They are a lot more versatile than a 3 jaw and the jaws are directly opposite each other as a 4 jaw for better grip strength.

      Comment


      • #4
        Nobody around here sells cast iron that I can find in the rough
        A ten pound barbell plate is the right size for that. Once you get over the 5 pound size they are usually pretty machinable since it is the cooling rate that determines how hard the iron becomes. Machine the boss with threads as a separate item and then mount the cast iron back plate to it with a press fit and some cap screws.

        Free software for calculating bolt circles and similar: Click Here

        Comment


        • #5
          If you Google "1-3/4" x 8 backplate" you will get lots of hits. Here's one already machined for a Bison Set-Tru chuck: http://brassandtool.com/Backplate-Adaptors.html

          Scroll down.

          RWO

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          • #6
            If you want to reconsider CI you may want to take a look at this:

            http://www.travers.com/product.asp?R...319-63-325-610

            Yes CI is messy, but it tends to be more stable than steel which is some thing you want in a backing plate.

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            • #7
              You don't show your location so hard to suggest a dealer but Bison offer blank cast iron backplates for not too much money. Depending on your part size then a Bison 5C set true collet chuck might be an option too.

              Pete

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              • #8
                Originally posted by RWO
                If you Google "1-3/4" x 8 backplate" you will get lots of hits. Here's one already machined for a Bison Set-Tru chuck: http://brassandtool.com/Backplate-Adaptors.html

                Scroll down.

                RWO

                And that's $220.00, yes I saw it, no I'm not spending an additional $220 for threaded cast iron. Maybe my google-foo is weak but the rest are discussion hits lamenting the scarcity of that thread.

                Comment


                • #9
                  Originally posted by 3t-
                  Photoman,

                  What is your brand/model lathe that it has this nose thread?
                  Grizzly G0602. Nice lathe and normally I could just modify the available 3 and 4 jaw plates but this needs a tall boss and would leave nothing of the back of the plate after that was turned into it.

                  Comment


                  • #10
                    Originally posted by Dr Stan
                    If you want to reconsider CI you may want to take a look at this:

                    http://www.travers.com/product.asp?R...319-63-325-610

                    Yes CI is messy, but it tends to be more stable than steel which is some thing you want in a backing plate.

                    The main issue to me is that the price for the unfinished blanks is up near $100 and then you have to ship that too. Where I can get a 2 1/8" thick cut of a 6" steel round for $45 and just drive home with it. A little less butt puckering to work on too at that price. The 6061 is $38 for the same size. No 2024 offered locally that I have found yet (Kansas City, MO).

                    The barbell is interesting but I am concerned with mystery metal of unknown formulation and spinning up a 22lb chuck at up to 2400RPM. The idea to bolt the rear plate to the boss and threads is a nice one though. Evan, you always have a neat suggestion and imaginative approach.

                    Appreciate all the input coming in.

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                    • #11
                      I would be concerned at 2400 rpm as well. My lathe only does 850. Is the new chuck rated that high?
                      Free software for calculating bolt circles and similar: Click Here

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                      • #12
                        Looks like the steel round would be your best bet.

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                        • #13
                          MSC, Mcmaster Carr? offer cast iron cut to length. One other point. The cast iron will thread much easier and be slightly self lubricating and softer so less wear and tear on your spindle nose. But oil is still simple to do with steel backplates.

                          Pete

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                          • #14
                            Originally posted by Evan
                            I would be concerned at 2400 rpm as well. My lathe only does 850. Is the new chuck rated that high?
                            Chuck is rated to 4000 according to the specs. However I see that Grizzly also now has a Bison 5" for about the same price. That may be less of a monster to mount up. I know the 6" 4 jaw is not real fun to move around.

                            Comment


                            • #15
                              For a cut to size piece of gray iron, you will be hard pressed to beat this one:
                              http://www.metalexpress.net/cgi-bin/...dad32486be69d3

                              RWO

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