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  1. #1
    Join Date
    Aug 2006
    Posts
    19

    Unhappy boring bar chatter

    Hi Everyone,

    I have started a job, and it went so well to start, but now the boring bar will not stop chattering. We tried changing the insert first, then moved on the speed and feed changes. We even tried changing the depth of cut to no avail.

    Thanks



    If it would help, I could download pics of the parts.

  2. #2
    Join Date
    Aug 2005
    Posts
    197
    If possible shorten the lenght that the tool sticks out and use a positive type insert. General rule of thumb tool stick out less than 4* dia of said tool.

    P.S. spindle bearings can play a big part.

    Please post pics of Job and set up and materail type.

    John

  3. #3
    Join Date
    Dec 2005
    Posts
    107
    This boring bar, is it in a turning center or a machining center?
    A little more information could be helpful.
    What kind of material etc etc...Regards Walt

  4. #4
    Join Date
    Aug 2006
    Posts
    19
    Sorry guys,

    The material is 4130 steel. It is on a lathe and it is as short as it can be already.

    Pics to follow soon.

  5. #5
    Join Date
    Aug 2005
    Posts
    197
    can it be a bigger tool? and how thin a wall is the part?

  6. #6
    Join Date
    Nov 2005
    Posts
    73
    Try boring from the inside out to try and get under the chatter also an old trick to stop vibration is to wrap the boring bar with elastic bands . Helps absorb the vibration , next step carbide bar.

  7. #7
    try some thick tapping oil , rather than flood coolant ,if that's what you are using , maybe try using a used insert that is in decent shape , sometimes a new insert will chatter until it has some wear on it

  8. #8
    Join Date
    Jan 2004
    Posts
    3154
    Insert will need a very small nose radius to reduce cutter pressure - say .007 - .015"
    www.integratedmechanical.ca

  9. #9
    Join Date
    Sep 2006
    Posts
    49
    Use a positive insert with minimum corner, wrap boring bar and part with rubber bands slow RPM
    Dave Schell, SeaSchell Tackle Machining/Mfg./Design [email protected] 619 562-1835

  10. #10
    Join Date
    Oct 2005
    Posts
    162
    is the tool on center? how big is the hole you are boring? are you using the largest size boring bar possible? it can be a number of things.
    On the other hand, You have different fingers.

  11. #11
    Join Date
    Aug 2006
    Posts
    19
    having problems posting pics.

    The question has more to do with the fact that the first 15 pcs were perfect. Without changing anything, the chatter suddenly became a problem from one piece to the next. Now we can't get rid of it.

  12. #12
    Join Date
    Aug 2005
    Posts
    197
    Ah,
    I to have run into this situation before on bar stock turnered out to be the material was a little difrent in the mid of the bar stock than on the ends go fiquire like to drove me nutttsssss!!! It could be a chemical dif or mechanical like its ben work hardend. I would try a slighty higher feed rate and or more depth of cut to keep the tool loaded. Also what type of tool (insert) are you using (I.E. CNMG 431, CCGX 430 exc.) pluss lead angle of. Oh and material condition.

    Oh ahh is this a first op or 2nd and or 3rd? just asking cause I have seen parts change by diffrent ops, you know one guy may be more agressive than the other and or vis/versa just a thought.

    John

  13. #13
    Join Date
    Jul 2005
    Posts
    12177
    Did the chatter start when you began using material cut from a different bar? I have had a similar thing happen with leaded steel and my conclusion was that one bar was slightly different. maybe a little bit harder or something, tool deflection also changed and sizes changed.

  14. #14
    Join Date
    Mar 2006
    Posts
    12
    attach some lead wheel balancing wieghts to the back of the boring bar as close to the tip as possable. use hose clamps to secure the whieghts if the hole size allows or masking tape if hole is close to the bar.

  15. #15
    Join Date
    Mar 2003
    Posts
    4826
    What kind of tool mount system is used on this lathe?

    What diameter bar?

    What insert are you using?
    First you get good, then you get fast. Then grouchiness sets in.

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  16. #16
    Join Date
    Aug 2006
    Posts
    19
    Thanks for all your help guys.
    Sorry I have not replied in so long, but I was very bussy with these jobs.
    We have found that there is probably the material being different with every bar like was mentioned. Apperantly, the tolerances for the ingredients of materials is quite loose, so they vary.

  17. #17
    Join Date
    Sep 2006
    Posts
    49
    Not suprising......
    last placed I worked we had parts we had been making for years...never a problem. Then we had a batch that had all kinds of issues, finish,warping after cuts, holding size, etc. Turns out even though we bought material, (2024-T4) from same supplier as always we hadn;t specified "Domestic". They substituted "Offshore". Even though it was certified & met all chemicals & properties the variences caused the above referenced issue. It is why when at all possible I specifiy "Domestic" material. Why cause myself grief.
    Dave Schell, SeaSchell Tackle Machining/Mfg./Design [email protected] 619 562-1835

  18. #18
    Join Date
    May 2006
    Posts
    196
    I don't know how much room you have to work with, but a set of vise grips clamped onto the back of the bar does wonders.

  19. #19
    Join Date
    Aug 2006
    Posts
    20
    Sometimes a good way getting vibration marks off the part is using low rpm and much higher feed.

  20. #20
    Join Date
    Oct 2006
    Posts
    10
    Been a long time since I operated a lathe or CNC machning centre, 20 odd years since I left the trade, but I recall we used to use all of the above methods and also lifting the bar slightly above centre sometimes helped.

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