Machining a 36" diameter bushing. - Page 2
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  1. #21
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    How did you manage to get a picture of my Myford doing a bush!

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  3. #22
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    Quote Originally Posted by macchi7 View Post
    How did you manage to get a picture of my Myford doing a bush!
    He's making a scale model of the QE2, that's for one of the prop shafts.

  4. #23
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    Quote Originally Posted by cuttergrinder View Post
    Its not a powered compound. It has a rapid traverse on the carriage. Its actually a cable drum lathe. It cuts leads rather than threads per inch.
    Here is a couple more pictures. The one is showing the grease grooves i have to bump over. The other picture is another set i made. They are getting some holes drilled on the boring mill.
    Attached Thumbnails Attached Thumbnails 20190917_122514.jpg   20190917_122440.jpg  

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  6. #24
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    I logged in just to "like" your post. Great work.

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  8. #25
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    Nice work! Big parts, not too complicated. Me like!

  9. #26
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    Quote Originally Posted by Milland View Post
    Hi Joe,
    OP's already stated it's a solid bar, but I'm curious about the "1/8th" statement. I'd agree if they were just stacked together they'd be significantly less stiff, but truly bolted together (not just in the middle) I think they'd be much closer to the solid value.
    It's straight out of Roark, formulas for stress and strain. PDFs are available on the web. Basically, the stiffness of a beam is proportional to the cube of the dimension being bent: (1/2)^3= 1/8.

    Think of a floor joist. Why is it 2x8 or 2x10, with the long dimension vertical?

    If that boring bar were in fact two rectangles bolted together, running two weld beads down the two outside seams would largely recover the stiffness. Bolts are not nearly as stiff in shear as a long weld. It's useful to think about the mechanical advantage between the two half-beams as the stack is bent.

    Now, for a boring bar, there are both bending and twisting forces, and chatter can use either or both.

    As well, might even have a damping advantage with the two faces rubbing together helping to convert some vibration into heat. But there might be a geometry drift due to that heat, so perhaps a bit of a gamble.
    There will be some damping due to friction for sure, but the loss of stiffness will dominate.

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  11. #27
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    I see someone else uses old iron. Good job...

  12. #28
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    Is that another Monarch NN in the background?

    There's a local shop here in the city I live by that has two Monarch NN's and two N's the last time I was in there. Brought back memories. Ran one that came out of government storage forty years ago while I was in college. What a sweet operating lathe for it's size! Very nice work you done there. Thanks for sharing, Ken

    Ken

  13. #29
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    Quote Originally Posted by mllud22 View Post
    Pricey piece of bronze.
    That was my first thought as well. I assume it's hollow cast so not a huge amount of waste...

  14. #30
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    Quote Originally Posted by Joe Gwinn View Post
    It's straight out of Roark, formulas for stress and strain. PDFs are available on the web. Basically, the stiffness of a beam is proportional to the cube of the dimension being bent: (1/2)^3= 1/8.
    Sure, for two pieces laid on top of one another. But for a truly bolted section (again, not just the middle), the stiffness will not be hugely off the value of a solid bar. I agree that bolts don't magically pin parts together 100%, but done correctly you'll recover ~80% of the unitary stiffness.

  15. #31
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    thats a decent boring bar.. lotta torque on the tool post tho for sure! the "spring pass" must be .005 or more.. even in bronze.. (well maybe not on that dia)

  16. #32
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    Quote Originally Posted by LKeithR View Post
    That was my first thought as well. I assume it's hollow cast so not a huge amount of waste...
    They are cast in 2 pieces. The splits are milled and tack welded together and then turned. There is not a huge waste but i bet i got 300 lbs off that bushing. The 2 halves weigh about 1,600 lbs when i start.

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    Quote Originally Posted by 4GSR View Post
    Is that another Monarch NN in the background?

    There's a local shop here in the city I live by that has two Monarch NN's and two N's the last time I was in there. Brought back memories. Ran one that came out of government storage forty years ago while I was in college. What a sweet operating lathe for it's size! Very nice work you done there. Thanks for sharing, Ken

    Ken
    Yes the other lathe is smaller dia but longer. I believe it will swing 30" over the carriage x 20' long.

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  19. #34
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    There are (2) shops nearby that make very similar parts:
    1. Verticalseal in Pleasantville, pa: Vertical Seal Company
    2. us bronze in Meadville, pa: Welcome

  20. #35
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    Only the best guy in the shop gets trusted with a piece of material that costs this much. Nice job, guys like you add a lot of value and credibility to the shops name .

    Make Chips Boys !

    Ron

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    Quote Originally Posted by Dupa3872 View Post
    Only the best guy in the shop gets trusted with a piece of material that costs this much. Nice job, guys like you add a lot of value and credibility to the shops name .

    Make Chips Boys !

    Ron
    You mean if i mess this one up , i cant order a replacement from mcmaster-car. Now im nervous. Lol

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  23. #37
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    Quote Originally Posted by Milland View Post
    Sure, for two pieces laid on top of one another. But for a truly bolted section (again, not just the middle), the stiffness will not be hugely off the value of a solid bar. I agree that bolts don't magically pin parts together 100%, but done correctly you'll recover ~80% of the unitary stiffness.
    Hmm. How does one achieve that 80%? Especially in twisting.

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    Quote Originally Posted by Joe Gwinn View Post
    Hmm. How does one achieve that 80%? Especially in twisting.
    Because stiffness is material strain at some MoI. If you have the same MoE, and have bolted along the edges (just as you'd see with fabricated box beams in older built-up bridges), then whatever load you're applying will try to strain material to (essentially) the edges of the geometry, and create the counter to applied load. So not the full equivalence of a solid element, but a good portion of it.

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    Quote Originally Posted by Joe Gwinn View Post

    It's straight out of Roark, formulas for stress and strain. PDFs are available on the web. Basically, the stiffness of a beam is proportional to the cube of the dimension being bent: (1/2)^3= 1/8.
    This also assumes that the deflection is not high enough that the second beam is under load. The complexity of the interaction if they're not attached makes for a fun analysis problem or a pain in the butt depending on your feelings about the work.

    Attaching the beams at the end using almost any method will put the setup a lot closer to the original value than the 1/8 value.

    Now, this would kind of beg the question of why someone would design it using two separate bars, but as neither OP's work nor anyone else as far as I know has, I think we can just close the case on it.

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    Quote Originally Posted by cuttergrinder View Post
    Here is a couple more pictures. The one is showing the grease grooves i have to bump over. The other picture is another set i made. They are getting some holes drilled on the boring mill.
    How exactly do you do the grooves?? very cool!!


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