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Thread: Safety Question

  1. #1
    Join Date
    Aug 2006
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    Hesperia, CA
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    859

    Default Safety Question



    Long story how I got in this mess, lol, but here I am. I need to lengthen the register/clearance area on this backplate. It's .025 from bottoming on the spindle like it's supposed to, but since I did the original work in my 3 jaw I'm wanting to set up in a 4 jaw to get concentric for the cut.

    This big 10" is the only 4 jaw I currently have mounted. This backplate will solve that issue BTW because it's for a sweet little 8" I got from BadDog that's much appropriate for an 11" bench lathe.

    As you can see I'm having a jaw problem. If I go with the middle step on the jaws there's too much extension. Won't clear the bed. But I can't go on the outer most step because then all 4 jaws run into each other before they reach the piece.

    So I compromised!

    It's tuned in to under .0005. Planning on 360 rpm to cut about a quarter of an 8 tpi thread out. Should I throw the switch?

    SP

  2. #2
    Join Date
    Jul 2005
    Location
    Derry, NH
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    Default

    If you throw the switch, i wouldn't want to be standing too close to it ... and i'd be taking very light passes ...

    I'm curious to see what others have to say ... if everything went the way its supposed to i can't see how its any different than having a solid jaw. BUT if you try to hog out to much or its not tightened all the way and it slips then you end up flinging a chunk of metal out ... so the cost/benefit ratio changes!

    360 rpm doesn't sound too horrific though - any chance at moving slower?

  3. #3
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    Aug 2006
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    Default

    Quote Originally Posted by Fasttrack

    360 rpm doesn't sound too horrific though - any chance at moving slower?
    I just did the math and I probably should slow down. I think a 2.25" bore at 360 rpm is around 180 sfm. Half that should be fine for cast iron.

    No wonder I was smoking the garage the other day .....

    SP

  4. #4
    Join Date
    Aug 2006
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    Hesperia, CA
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    859

    Default Plan B

    What if I cut the packing pieces down to a size that doesn't stick out past the jaws? That would certainly LOOK a lot less dangerous.

    SP

  5. #5
    Join Date
    Nov 2007
    Location
    coastal Oregon
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    78

    Default 4 jaw

    pntrbl,
    If you could use some spacer blocks the same thickness, but smaller in the other 2 dimensions it would be safer. The amount of extra metal in the blocks that extend beyond the jaws is just extra mass that's trying to fly outward from centrifugal force, thereby trying to lever the work out of the chuck. The excess metal that extends beyond the sides of the jaws in the plane of rotation is trying to open the jaws at speed. Maybe some saw work?
    Lwbates

  6. #6
    Join Date
    Jul 2005
    Location
    Derry, NH
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    Default

    Yeah i would think that somewhere in the 100 to 150 rpm would be good. I think the recommended SFM for cast iron with a HSS cutter is 60-80 which, at 2.25 diameter, is about 100 rpm. Not sure what your using though - if you have carbide i guess it needs to be faster. Don't have those memorized but i'm working on getting HSS with various materials memorized.

  7. #7
    Join Date
    Jul 2005
    Location
    Derry, NH
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    Default

    centrifugal force...? There's no such thing ...

    Technically there is only the centripedal force mainting the circular path; the percieved force trying to deviate from the circular path isn't a force at all but the bodies inertia that you are feeling.

  8. #8
    Join Date
    Aug 2006
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    Hesperia, CA
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    Default

    Now don't get "physical" on me FT! LOL! I ain't smart enough for that. But I will cut them spacers as lwbates suggests and drop some r's. And maybe wear a helmet ......

    SP

  9. #9
    Join Date
    Jul 2005
    Location
    Derry, NH
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    Default

    Sounds good!

    Nice looking lathe by the way! Looks like its brand-new. Did you just restore it? I know i saw a nice rebuild on here a while back but i can't remember now whose it was.

  10. #10
    Join Date
    Apr 2001
    Location
    Clinton, WA
    Posts
    955

    Default

    pntrbl,
    I know this might be more work but you could machine a threaded arbor that threads in about half the depth of the back plate, mount the threaded arbor in the 4 jaw with the jaws oriented a little safer, screw on the back plate and center, then machine your register/ clearance area.
    Mark Hockett

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