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  1. #1
    Member
    Join Date
    Aug 2006
    Posts
    114

    Loose insert screws

    Running feed mills the insert screws comes loose before the insert life has expired. I think it is the main cause of insert failure. I found that every feed mill suffers from this issue. Iscar, Ingersoll, ZCC, Sumi and Kyocera all do it. I've taken to checking the insert screw torq at about half life of the insert and found that 80% of the time at least one screw has loosened. This policy has increased not only insert life but the life of the tool body. Why does this happen? Why is this so pervasive across all manufacturers? Most Importantly. What can be done to mitigate it other then stopping production to check for it?
    "Teach the ignorant, care for the dumb, punish the stupid."

  2. #2
    Member
    Join Date
    Jun 2015
    Posts
    3801

    Re: Loose insert screws

    hy

    on one side, maybe the tool is pushed too much, or maybe there is something not so rigid about the fixture or spindle or the tool itself

    on the other side, they need to sale, and quality sometimes may be compromised, even if the product video shows promising



    a high-feed mill handles forces and frequencies > than same size end mill, simply because it is built for mrr+

    is not cost efective to use an integral tool, so using inserts means lower cost; but, just to show something, imagine an integral tool : it has no screws down there, and it is being secured in a toolholder, with a big screw ( or maybe 2, etc ), and those screws are located close to spindle face : so, they are bigger, more resistant, and the cutting forces/reactions that reach them, are being dumped along the way by the toolholder, and the screw itself, being near the spindle, is in a more rigid area

    thus, those tiny screws that hold the insert, are in the war zone



    a small threaded ansamble can not deal with stress as ok as a biiger one, and also, the mill insert is subject to more contacts with the material, because it is making and losing contact at each spindle revolution, while on a lathe, things are different :thus, in other words, same screw for a similar insert, on a lathe toolholder, won't come loose as fast as on the mill



    what to do ?

    you may scan the market, and try products until something happens ( like you get lucky, or bored, or both )

    decrease the diameter of current tools; it should hang on better, as long as screws size is identical, but is not a must, because a smaller tool with similar screws, may have a shorter id thread

    use secure paste, like locktite, or how is it calledd ? but the drawback, is that it will require more force to unscrew the tiny screw, and his head may get damaged

    can craft your own milling head; here are some tips :
    ... must be heavy/heat treat for high forces(mrr+), or light for high rpms(mrr-)
    ... besides the middle screw, consider a 2nd clamp, or entirely redesign the insert bed
    ... the more rigid the insert clamp it, the less inserts you will be able to mount on it

    if you have experimented enough inserts, chose those ones that you like, and for them, start creating a milling head; an y lathe will make this job easier

    if you wish, i will help you / kindly
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  3. #3
    Member
    Join Date
    Jun 2015
    Posts
    3801

    Re: Loose insert screws

    pls check attached : the 2nd screw has the roll to prevent the insert from lifting, because of oscilations, thus it does not allow the insert to behave like a boat on wavy water

    it has to be a bit more far away from the main screw, not as close as in that image, where it is so because it delivers coolant; however, when distance is increased, it has to be checked that it won't lift the insert from the holder, thus it has to push the insert in a zone where is still contact between insert and holder, and this may vary, since contact is not among entire insert's bottom face

    also, even if bottom contact is ok, thus even if insert seats thight in the toolholder, there still may appear lift, simply because the 2nd clamp, when contacts the insert, tends to rotate it, as surfaces that come in contact are not plan-paralel

    and last, but not least : if lift appears, and can not be eliminated, then is still safe to use the insert as long as the cutting forces won't make the insert to balance; thus the clamp force that generates lift, has to be > cutting force

    there are such systems ( middle screw + side clamp ) also for mills, but they are not so common

    is possible to modify an existing one : just tap it ( maybe face it before ), and craft some clamps in house / kindly
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  4. #4
    Member
    Join Date
    Jan 2005
    Posts
    14730

    Re: Loose insert screws

    Quote Originally Posted by Species8472 View Post
    Running feed mills the insert screws comes loose before the insert life has expired. I think it is the main cause of insert failure. I found that every feed mill suffers from this issue. Iscar, Ingersoll, ZCC, Sumi and Kyocera all do it. I've taken to checking the insert screw torq at about half life of the insert and found that 80% of the time at least one screw has loosened. This policy has increased not only insert life but the life of the tool body. Why does this happen? Why is this so pervasive across all manufacturers? Most Importantly. What can be done to mitigate it other then stopping production to check for it?
    Sounds like you are over loading, or they are not torqued up to the correct torque, and the screws are stretching under load, I have never seen that happen before and I have some Face Mills up to 300mm / 12" down to single insert 19mm / 3/4", mine on some seem to get tighter as they can be tough to get lose sometimes.

    Have you replaced the screws and used the correct torque
    Mactec54

  5. #5
    Member
    Join Date
    Jun 2015
    Posts
    3801

    Re: Loose insert screws

    idea from attached hit me a few days ago
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

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