Machining a 36" diameter bushing. - Page 3
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  1. #41
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    If the 2 beams were merely in full contact, then it seems the stiffness should be 1/8 * 2 = 1/4 that of a solid bar, not?

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    This is a great post by the OP. You read the title and you're like, "Oh dear heavens it's gonna be a guy trying to make a massive part on the wrong machine, like a Bridgeport mill or something, and everyone's going to be arguing about getting a proper tool or coming up with increasingly outlandish methods to make the thing". So you click on it with a rising sense of outrage about the things you haven't even read yet, and instead you get his massive boring bar giving the middle finger to your technical pretensions. Nice job!

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    Quote Originally Posted by digger doug View Post
    Wow. I'm shocked at the low price. It even comes with a DRO! ;-)

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    Quote Originally Posted by Milland View Post
    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.
    Well, I'll probably hit the books this weekend. My instinct is that it's difficult to get that kind of stiffness out of ordinary bolts, no matter what. In the old days, they used hot rivets, which do cinch up quite tight.

    What would work would be high-tensile structural bolts that are torqued to 70% of yield, using hydraulic tools, with a bolt tang that snaps off when the proper torque or strain level is reached. I don't recall the standard number, something like A325, but they are used in steel framing in place of welding, in fields of bolts in a hex grid. They did care about use of paint on slip-critical surfaces, even at that clamping pressure level.

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    Quote Originally Posted by cpifer3 View Post
    How exactly do you do the grooves?? very cool!!
    The grooves are cast in .

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    Quote Originally Posted by digger doug View Post
    I showed this to the boss

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    That Bullard doesn't have enough column height to setup and bore out that casting IMO. That's probably why they are letting it go cheaply.

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    Quote Originally Posted by 4GSR View Post
    That Bullard doesn't have enough column height to setup and bore out that casting IMO. That's probably why they are letting it go cheaply.
    You are probably right. Also dont know how i could mount my 8' boring bar on there . Lol

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    I tried to bore the bushing with my next smaller boring bar which is 4" and it just vibrated horribly. The big bar didnt chatter at all.

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    Quote Originally Posted by 4GSR View Post
    That Bullard doesn't have enough column height to setup and bore out that casting IMO. That's probably why they are letting it go cheaply.
    I'm not seeing what your seeing.

    The cross rail looks like it may just be high enough as it sits, and appears it can go higher.

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    Quote Originally Posted by digger doug View Post
    I'm not seeing what your seeing.

    The cross rail looks like it may just be high enough as it sits, and appears it can go higher.
    It may go high enough but getting a big enough boring bar in there may be a challenge.

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    Quote Originally Posted by NRDock View Post
    If the 2 beams were merely in full contact, then it seems the stiffness should be 1/8 * 2 = 1/4 that of a solid bar, not?
    No, because the neutral axis of the system is now between the bars, so each half is effectively taller.

    Quote Originally Posted by Joe Gwinn View Post
    Well, I'll probably hit the books this weekend. My instinct is that it's difficult to get that kind of stiffness out of ordinary bolts, no matter what. In the old days, they used hot rivets, which do cinch up quite tight.

    What would work would be high-tensile structural bolts that are torqued to 70% of yield, using hydraulic tools, with a bolt tang that snaps off when the proper torque or strain level is reached. I don't recall the standard number, something like A325, but they are used in steel framing in place of welding, in fields of bolts in a hex grid. They did care about use of paint on slip-critical surfaces, even at that clamping pressure level.
    Fully admitting that I'm just throwing fuel on the fire here. Why not move to torque+angle if you're going to go that far? A snap off tang can do a good job of maintaining desired torque, but torque carries a less than ideal correlation to installed fastener tension.

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    Quote Originally Posted by NRDock View Post
    If the 2 beams were merely in full contact, then it seems the stiffness should be 1/8 * 2 = 1/4 that of a solid bar, not?
    No, stiffness varies as the cube, not the square, of the cross-section width in the relevant dimension. Look at Roark's formulas for stress and strain for the actual formulas. There must be a derivation somewhere as well. Also, it's pretty easy to test.

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    Inquiring minds need to know............. If the standard press fit is generally .001 per inch of diameter, does that mean that bad boy gets .036" of press?

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    Quote Originally Posted by mark costello View Post
    Inquiring minds need to know............. If the standard press fit is generally .001 per inch of diameter, does that mean that bad boy gets .036" of press?
    The body of the bushing in 33.655. I have no idea what the bore size of the housing is.

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    Out of interest, how do you measure the diameter that accurately. Do you have some really big micrometers or what?

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    Quote Originally Posted by Bill D View Post
    Out of interest, how do you measure the diameter that accurately. Do you have some really big micrometers or what?
    Yes we have big mics. I think we have to 54" mics.
    Attached Thumbnails Attached Thumbnails 20170118_135501.jpg  

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  22. #59
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    Quote Originally Posted by cuttergrinder View Post
    Yes we have big mics. I think we have to 54" mics.
    Man, that's impressive. The little 1/4-40 guy on the end just looks so out-of place. Must be a bear to make sure you have both ends on center, or do you use a jig?

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    Quote Originally Posted by BoxcarPete View Post
    Man, that's impressive. The little 1/4-40 guy on the end just looks so out-of place. Must be a bear to make sure you have both ends on center, or do you use a jig?
    We didnt make the mics. Im not sure who manucatured them. These are not the mics i used on the bushing. Just a picture i had on my phone. I dont think this picture was even the biggest ones.


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