Ringing on large dia turnings?
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  1. #1
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    How do you stop the harmonic ring when facing large plates?I have tried slower and faster and even packing rags behind the plate but still get that annoying ring.Help me out what is the trick?Cory

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    Use a small radius insert as is practical, and fairly aggressive feedrate, especially when roughing. It might prove beneficial to switch to ceramic inserts in order to boost the surface speed up into another range that may not get so chattery.

    Inevitably, I think it usually ends up being necessary to drag a spring loaded wear block or perhaps a wheel against the surface. Think about how to be safe before going this route!

    Perhaps some strong permanent magnets could have been secured beneath the plate to give some pull to help provide a contact point to drain some of the vibration into the faceplate.

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    How big is "large?" How thick is the plate? What is it made of? What tool are you cutting it with, how fast, and with what feed? Depth of cut? What lathe? How are you holding the workpiece?

    I've never had a harmonic ring that wasn't due to a poor fixture, but I've never been involved in what I would consider large facing operations.

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    Get some of those large, wide, weighted belts that go around automotive brake drums when they are turned. It makes all the difference in the world on finish too, especially considering many modern rotors are "composite", or have a thin steel hub with a cast iron ring on the outside. Not exactly a rigid setup...

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    Try wrapping one or more rubber tarp straps around the OD of the plate.

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    If you can get wedges of some kind behind the chuck jaws near the center, you'll kill the ring. It'll jack the freq way beyond anything likely to cause problems.

    Think of this like a gong. It's the distance from center to the edge that is causing the problem. Cut it in half and you'll just double the freq, which will just be the next octave harmonic. Catch it somewhere close to the middle, but not in the middle and you'll drive the harmonic way out.

    A hunk of lead bolted to the center will do wonders, too.

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    I second the straps or use a leather belt. I was also shown to use modeling clay packed into the part depending on what it look like.

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    I bought one of those things they used to use on brake rotors/drums to stop harmonic ringing.Slip it on the piece to be turned,inflate it and go to work.Works just fine as long as the piece isn't so narrow it won't hold on.I've even used it on non circular pieces but had to be careful it didn't come off.Can only turn at moderate speeds for obvious reasons.

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    I've had good luck on large diameter thin wall tubing by packing the side opposite the cut with a layer of DUXSEAL It's kind of like modeling clay. It really helps damp out vibrations. I'd imagine it would work on face turning as well.

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    I normally use jack screws between the chuck and the workpiece. Most of our larger chucks have T slots, but if you dont have this option the pressure should keep the screws in place. Just dont stand directly in front of the chuck.

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    Try a piece of foam rubber thick enough to require a significant amount of compression.

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    Just dont stand directly in front of the chuck.
    Yikes!!

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    B Madar uses the same method I do. Our chucks all have T-slots also (there are small drilled and tapped holes at the end of the slots that you can screw a SHCS into to prevent the t-nuts from "escaping"), but where I used to work whenever I needed to use jackscrews on a chuck with no T-slots, I just safety wired them to the chuck jaws, so that way even if they come loose, they can't fly out.

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    I normally use jack screws between the chuck and the workpiece.

    B Madar uses the same method I do.
    Another vote for jack screws. As close as the bolt bin or the clamp rack on the Bridgeport. Even on the 24" chuck, they rarely eject, and I've never wired or secured one in.

    Essential on the 48" faceplate on the Niles, big parts squeal like a pig

    Jack screws are just as helpful on the Bpt, when the Kurt jaws are in the outside position and the part is much wider than the vise. Four, sometimes six, make a huge difference in finish quality.

    -------------
    Barry Milton

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    I normally use jack screws between the chuck and the workpiece. Most of our larger chucks have T slots, but if you dont have this option the pressure should keep the screws in place. Just dont stand directly in front of the chuck.
    Bingo!! This is the method I use and it works great. You have to be careful with the jacking screws so you don't put to much pressure and push out the face of your plate if it's kind of thin. Sometimes it's ok to tack weld them to the back of the part just so the jacks can't fly out.


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