Boring bar chatter cure... I don't believe it!
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  1. #1
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    Default Boring bar chatter cure... I don't believe it!

    I have read a couple times (on this forum) that loosening set screws on a boring bar can sometime cure stubborn chatter issues.
    I have a very sturdy setup with a 3/4" bore bar with less than 3x stickout. We struggled with a persistent chatter issue that could not be cured with any combination of speed, feed or DOC. So, when I setup the same part again yesterday, I decided to try loosening all but the first set screw on the tool holder block.
    100% fixed. Not only that, but I have varied the parameters wildly and now I cannot generate chatter with any conditions. So, I went to very heavy roughing passes and an ideal finish pass for a fast, perfect results on every part.
    Simple solutions are not always intuitive.
    Thanks to the random comments in prior posts for putting this idea in my head.

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    Your solution could have been found by the guy who forgot to tighten all his screws. Tightens the first one then gets called to the phone.
    Comes back and has a nice day. Maybe it's a guess but I think what you did was change the resonant frequency. Would like to see a animated
    video of before and after. You would think what you did was to make things worse. I'm going to try this one day.

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    Yes with resonant systems, changing stiffness to change the resonant frequency can be very effective. Changing mass can work too (e.g., securing a weight to the vibrating system).

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    I’ve done the “Wrap the bar in a piece of lead” thing with good results.

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    There are many situations in machining where tightening can be over done creating less than stellar results, often caused by undertightening something and making scary noises and sometimes sparks too. It is often hard to find and maintain that sweet spot.

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    Having only one screw tight is not something I think I would have tried, so thank you OP for sharing that experience.

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    I forgot to fully tighten a cut off tool in my Doosan a few days ago. Results were not so pleasant. hahahaha.

    But yea, sometimes putting some alum between the screw and the boring bar helps as well. I've seen bicycle tire tubes wrapped around big boring bars before.

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    Quote Originally Posted by fmari --MariTool- View Post
    I've seen bicycle tire tubes wrapped around big boring bars before.
    I sometimes wrap a bike tube around the work, if it's the sort of shape that rings easily.
    The difficulty is getting the tube to stay there and not be in the way of anything.

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    I always only use one set screw. Typically it's the one on the end or furthest from the insert.

    Brent

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    Quote Originally Posted by jwmelvin View Post
    Yes with resonant systems, changing stiffness to change the resonant frequency can be very effective. Changing mass can work too (e.g., securing a weight to the vibrating system).
    I sometimes use a 2x4 and press it gently to a piece of metal that might vibrate. Like if it was in a vice and the ends were not as stable as the middle section.
    Works pretty good in a situation that has few options.

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    Dad had a bar ground from a long 3/8 square bit. He hung the carriage lock wrench on the tail end of it to kill the chatter.

    'But, that's completely on the other side of the toolholder and screws. WT ...'

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    Quote Originally Posted by jwmelvin View Post
    Having only one screw tight is not something I think I would have tried, so thank you OP for sharing that experience.
    It is the exact opposite of safety. So the decision is to risk a tool coming off a holder or getting a crappy finish.

    I think that when you loosen setscrews from front to back to get the chatter to go away you should have more than one setscrew holding the tool.
    I would still go for it if there was only one screw out of four tight, but I would be careful and take light cuts.

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    Quote Originally Posted by rons View Post
    It is the exact opposite of safety. So the decision is to risk a tool coming off a holder or getting a crappy finish.

    I think that when you loosen setscrews from front to back to get the chatter to go away you should have more than one setscrew holding the tool.
    I would still go for it if there was only one screw out of four tight, but I would be careful and take light cuts.
    It's a fully captive round hole bar holder and the set screw is landing on a flat. The bar is not going anywhere. I've maxed out the speed, feed and DOC according to the ISCAR insert parameters and it makes a beautiful swoosh sound.

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    Quote Originally Posted by yardbird View Post
    I always only use one set screw. Typically it's the one on the end or furthest from the insert.

    Brent
    Interesting. I am using the one closest to the insert. I suppose it would be possible to cure different problems by tightening different setscrews. I'll keep that in mind.

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    Quote Originally Posted by JBNimble View Post
    It's a fully captive round hole bar holder and the set screw is landing on a flat. The bar is not going anywhere. I've maxed out the speed, feed and DOC according to the ISCAR insert parameters and it makes a beautiful swoosh sound.
    I verify by tightening the rest and see if the chatter comes back.

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    I think what you effectively did was lower the resonant frequency so that you're cutting well above it.

    I learned about that from someone much smarter than me, years ago.

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    Quote Originally Posted by rons View Post
    It is the exact opposite of safety. So the decision is to risk a tool coming off a holder or getting a crappy finish.

    Says the guy who just said he holds a piece of 2x4 against the part being cut in a (presumably) CNC machine with the door open...

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    I believe Jashley mentioned using electrical tape or something under the holder to get some form of "de-vibe" action. dampening of sorts...?

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    So the only thing my 12CK does for the last decade or more is enlarge an over 2 inch bore by an inch over .15 deep. Total hack work,not fussy.

    Use a brazed carbide cause cheap.

    Chattered up a storm

    tried everything adjust tool height faster slower feed[feed is only limited by grip of jaws on the part]

    solution?

    run the Aloris loose.

    I always meant to ask for advise here but I was going to give it one more go at finding a solution first

    So maybe that is the solution

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    Quote Originally Posted by gustafson View Post
    run the Aloris loose.
    With the holder just hanging on the dovetail?

    I've had mine either vibrate loose ... or I forgot to tighten it ... and it cuts just beautiful. Insert OD turning tools mostly. 4140PH, 416, maybe some alum. Holds dimension too. Weird.


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