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  • #16
    JC, it's funny you should mention a 4 jaw to clean up the top of the compound. This whole exercise is about making my own backplate to mount up a 4 jaw. Kind of like like the chicken or the egg ....

    Or a vicious downward spiral into all things machine I find myself being sucked into!!!!

    I should probably break down and just buy a damn backplate. Stubborn.

    SP

    EDIT, Prehard 4140 is what I'm working with.

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    • #17
      Originally posted by pntrbl
      EDIT, Prehard 4140 is what I'm working with.
      That is not helping and is probably a major source of your grief.
      Jim H.

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      • #18
        What make is your lathe, S-B ? BTW nice paint,did you restore this piece yourself ? I see a turret tailstock just curious.

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        • #19
          Yes an 8TPI thread is a big chipload at full depth. having a rigid setup is most important. tool pressure from upside down tool is lifting the compound and all, not pressing down like it's designed. If you want to cut on the back side, start with tool inside the bore, in relief groove, cut toward tailstock, Spindle in reverse. Now try to figure out which way to point the compound-left or right I never could get it right. Good luck.

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          • #20
            Originally posted by JCHannum
            That is not helping and is probably a major source of your grief.
            No kidding, A flame cut HR plate would have been fine.

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            • #21
              The lathe looks Logan-like.
              Can't tell if it has a flat back way or not, but the headstock looks like an 11" Logan, and that looks like an "automatic" apron.

              The light deal under the tool holder..... Be sure that the long overhang of that thing isn't sitting on the compound "hump". There's a lot of toolholder back there, and if the compound has ever been re-faced, the "hump" may be slightly above the seating surface back there, not cleaned up because it's "out of the way" except for that thing you have .

              Agree on the humongous overhang being a problem. I think I'd pull the crosslide back, and run the compound forward until the whole compound slide way was being used. A little stronger, and also less movement that way.

              Don't think 8TPI should be a problem.

              Do think 4140PH is more of a bear than required..... I'd have gotten a $13 unfinished cast iron backplate from Victor Machinery... machines like a dream. 4140 isn't ideal for a backplate anyway, CI is probably better.

              Check all the gibs too, besides fixing the toolholder issues. i'd make a block to hold a couple sizes of bar, that would hold the bars right over the t-slot area, and forget the QC toolpost dealand that huge overhang you have now. You can make reducing bushings for smaller bars.

              That overhang is asking to snap the compound right off the machine if you have a jam-up. Not good, IMO.
              CNC machines only go through the motions

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              • #22
                Originally posted by J.Ramsey
                What make is your lathe, S-B ? BTW nice paint,did you restore this piece yourself ? I see a turret tailstock just curious.
                It's an 11" Logan. Model # 940-2, S/N 60214, but it's been modified here and there. No part of the machine I have not molested and/or fondled. Complete disassembly and I did the best I could putting it back together. Call it a labor of love or a flight of fantasy ..... but it's all mine now.

                SP

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                • #23
                  OK. I have read and re-read all the responses and thanx again. The PH4140 is just because my bro gets me a deal at McMaster. He works here in LA at the Santa Fe Spings facility, but unfortunately they only stock cast iron at the Chicago warehouse. He can't get it for me at the wholesale price. But who cares? LOL! I've scrapped enough 4140 even at wholesale I coulda bought an already threaded 2.25 backplate from Travers, MSC, etc.

                  But that's no way to learn.

                  So, the next attempt will be in cast iron. The next google will be Victor Machine per JTiers suggestion.

                  Thanx again, SP

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                  • #24
                    Glad to see you having a go of it rather than just buying the backplate.

                    If I am not completely comfortable with a setup, I try it out on a piece of scrap first. An expensive piece of stock or nearly completed part is not the ideal place to practice technique or determine if rigidity is adequate. Eventually, you really get to know your machines and what they will and won't let you get away with!
                    Location: North Central Texas

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                    • #25
                      Don't Scrap!

                      Where I work we repair alot of bad bores by boring the hole over size and then welding it so it can be rethreaded. Bore it slightly past where the bottom of the threads will be then weld it with 7018 rods.

                      mark61

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                      • #26
                        Victor machinery isn't as cheap as it was!

                        I bought a couple un-machined backplates at $13 per, but I can't find them on the site now, and the new catalog doesn't have them either. The ones they have a quite a bit higher.

                        As they used to say at work, "prices has went up".......
                        CNC machines only go through the motions

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