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  1. #1
    Join Date
    Sep 2015
    Posts
    17

    OD Chatter On New Citizen L20

    Hello, We've a brand new Citizen L20 and we're having chatter issue when turning. It's the first part we've tried running on the machine. The material is 8620, 11mm stock OD, 6.3mm finish OD, 28.75mm OD length. .01mm total tolerance. .8mm finish requirement. The 11mm stock is necessary due to a 10.1mm OD past the 6.3mm OD. The stock is precision stock although it doesn't appear to be polished. I've tried using a CCGT .4mm nose radius(Sandvik), VCEX .1mm nose radius(Sandvik) and currently a 3 series DCGT .2mm nose radius(Kennametal). The tool is on center. Any thoughts/suggestions on tooling? Current cutting parameters are 2000RPM .075mm/rev. 226SFM is slow, if I increase the RPM chatter comes into play. The chatter isn't always consistent either when running higher RPM, I've seen the first 3mm of the part be acceceptable then chatter the remaining length. I should also state that we're milling a flat on the part past the 6.3mm OD after the turning operation using a 6mm solid carbide end mill and you can see the back(bottom) of the end mill is dragging once the end mill is fully engaged, combined with the chatter issue it makes me think something is moving, lack of rigidity? Using M18 C0. in the program, couldn't find anything on a possible C-axis brake. The part is currently running with no taper. The guide bushing has extended land pads and from my understanding it's set correctly. I can hardly move the stock back and forth by hand through the gudie bushing, I'm able to rotate the stock by hand when the guide bushing is locked. Any thoughts/suggestions on properly setting the guide bushing? The main spindle(Z1) is as close to the guide bushing as possible when in production. I indicated the stock that was extended past the guide bushing, it's running true(concentric). I took out the main spindle collet and it appeared to have witness marks all the way around the front edge of the collet only, almost as if the stock spun in the collet and is only making contact with the very front of the collet. Any thoughts/suggestions? When I get back in the shop I'm going to run a short bar currently we are running 3 Meter bar length. I want to see if a short bar eliminates the chatter. I'm also going to make a temporary program that only skims the OD to see if less tool/machining pressure eliminates the chatter. What's the best practice to indicate the sliding head/turn tool to make sure it's correct? Thanks in advance, any help/insight is greatly appreciated.

  2. #2
    Join Date
    Jun 2010
    Posts
    4252

    Re: OD Chatter On New Citizen L20

    Chatter very often means something is loose, OR the tool is too floppy.

    Cheers
    Roger

  3. #3
    Join Date
    Feb 2011
    Posts
    353

    Re: OD Chatter On New Citizen L20

    there are many things to try
    is there bar vibration from the bar feeder ? this can cause funny things to happen
    what type of bar feed ?
    guide bushing sized correctly. There can be differences in the dia. (manufacturer's have tolerances on the guide bushing's) some people will say to lap the guide bushing in to size for best fit
    single pass or multiple passes/ segmented turn (rough and finish tools)
    inserts - what are the chip breakers FF,UF,LF WIPER/NON WIPER / any coatings on the insert, depth of cut ?. what is the manufacturers speed and feed recommendations?
    what kind of chip is the cut generating ?
    high pressure coolant at the cut ?
    sometimes there is a harmonic balance at certain point while machining you would have to move off that point (go faster/slower)

    good luck
    rcs

  4. #4
    Join Date
    Jun 2015
    Posts
    4131

    Re: OD Chatter On New Citizen L20

    oooh, is it you Nicu ?

    finish requirement 0.8 / hmmm : if you don't deliver the o6.3 in one shot, but you rough o6.3+0.8=o7.1, and after that you finish at o6.3±0.01, then, when you do the finish, the guiding bush may be holding air, instead of holding your part


    my advice : try delivering o6.3 in one shot, even if it won't deliver the tolerance and the nice surface rugosity : if there won't be chatter, than adjust the cutting specs and the offsets, so to deliver your part in one shot

    changing Z sense, among a long Z travel, may be an issue on a gang lathe


    if you still need to deliver the part with rough&finish, consider also holding the part with the 2nd spindle; however, so far, i have never used the 2nd spindle in Z sync motion with the 1st spindle, and i don't know if the controller allows such a thing

    i will let you know if i think of something else / kindly
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  5. #5
    Join Date
    Jun 2015
    Posts
    4131

    Re: OD Chatter On New Citizen L20

    Quote Originally Posted by deadlykitten View Post
    if you still need to deliver the part with rough&finish, consider also holding the part with the 2nd spindle; however, so far, i have never used the 2nd spindle in Z sync motion with the 1st spindle, and i don't know if the controller allows such a thing
    leave spindle 1 opened & feed with z2 ... so far i never tried it

    i hope the controller allows using a T for spindle 1, also for spindle 2
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  6. #6
    Join Date
    Sep 2015
    Posts
    17

    Re: OD Chatter On New Citizen L20

    Quote Originally Posted by rcs60 View Post
    there are many things to try is there bar vibration from the bar feeder ? this can cause funny things to happen what type of bar feed ? guide bushing sized correctly. There can be differences in the dia. (manufacturer's have tolerances on the guide bushing's) some people will say to lap the guide bushing in to size for best fit single pass or multiple passes/ segmented turn (rough and finish tools) inserts - what are the chip breakers FF,UF,LF WIPER/NON WIPER / any coatings on the insert, depth of cut ?. what is the manufacturers speed and feed recommendations? what kind of chip is the cut generating ? high pressure coolant at the cut ? sometimes there is a harmonic balance at certain point while machining you would have to move off that point (go faster/slower) good luck rcs
    IEMCA bar feeder, which I've no experience with. There are 4 rollers that engage the bar between the main spindle and bar feeder. When engaged, the bar runs true, but the bar shifts when the rollers make contact making me wonder if the bar feeder is aligned properly? No noise/vibrations are coming from the bar feeder though. I've attached some pictures. For the main spindle collet you can see that the material is only engaging in the first 4mm or so and the collet is marred. For the guide bushing it also appears as it's only engaging in the front. The picture of the bar stock depicts me clamping on the bar stock with the guide bushing by hand offline and rotating the stock. It shows it engaging in the front of the guide bushing and approximately 10mm back from the face of the guide bushing, that's it. How would I lap the guide bushing? I'm taking a single pass and the .01mm total tolerance isn't an issue, it's just achieving a consistent finish without chatter. One pic shows the inconsistency in the chatter, the first 3mm of the part is good then it chattered the remaining length. Anything over 2,000 RPM and it chatters. 2,000 RPM = 130SFM at the tool tip (6.3mm diameter) and 227SFM at the stock diameter (11mm). Slow, the manufacturer recommended from 450-650SFM if I recall correctly. Tried a Sandvik UM chip breaker to no avail, better luck with a Kennametal 5025 grade, high positive insert. Sandvik coating is PVD. Don't know about Kennametal. Non-wiper geometry. Long stringy chips, I say stringy but they have a nice helix to them just not breaking. Running high pressure coolant through the tool. I tried various RPM's all the way up to 7,000 to no avail. I didn't go below 1,800 RPM but that wasn't much different than 2,000 RPM. I took a skim cut, .5mm radial DOC at 8,000 RPM and the finish was great. Thank you for the help.

  7. #7
    Join Date
    Sep 2015
    Posts
    17

    Re: OD Chatter On New Citizen L20

    Quote Originally Posted by deadlykitten View Post
    oooh, is it you Nicu ? finish requirement 0.8 / hmmm : if you don't deliver the o6.3 in one shot, but you rough o6.3+0.8=o7.1, and after that you finish at o6.3±0.01, then, when you do the finish, the guiding bush may be holding air, instead of holding your part my advice : try delivering o6.3 in one shot, even if it won't deliver the tolerance and the nice surface rugosity : if there won't be chatter, than adjust the cutting specs and the offsets, so to deliver your part in one shot changing Z sense, among a long Z travel, may be an issue on a gang lathe if you still need to deliver the part with rough&finish, consider also holding the part with the 2nd spindle; however, so far, i have never used the 2nd spindle in Z sync motion with the 1st spindle, and i don't know if the controller allows such a thing i will let you know if i think of something else / kindly
    I'm taking it in one pass. The tolerance and finish are good when it doesn't chatter. Can you explain, "changing Z sense, among a long Z travel, may be an issue on a gang lathe"? Also, "i hope the controller allows using a T for spindle 1, also for spindle 2"? The controller allows spindle $1 and spindle $2 to be synced in the Z axis but how would I turn the end of the part if it's held in the sub-spindle? I've posted some pics including a pic of the main spindle collet. Thank you for your help.

  8. #8
    Join Date
    Jun 2015
    Posts
    4131

    Re: OD Chatter On New Citizen L20

    hi nicu / if you are cutting it in one pass + all things you described, i suspect an alignment / rigidity issue

    about the roller feeder i can't help, since i don't have such an equipment; maybe the rollers have a more powerful grip than the collet : did you tried with a shorter bar, that is not clamped by the feeder ?

    about the Z sense : if the guiding bush makes contact among 25mm dinstance, then you can not rough & finish for a Z>25 ( also Z20 may be an issue, because it is too close to 25 )

    the controller allows spindle $1 and spindle $2 to be synced in the Z axis : does this mean that you can clamp with both spindles, and turn something longitudinal ( among Z ) ? i never tried it ...

    how would I turn the end of the part if it's held in the sub-spindle? : depends on real scenario, but, in short : you may go with the 2nd spindle near the end of the part + cut off + continue machining @ 2nd spindle ... just saying; kindly
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  9. #9
    Join Date
    Sep 2015
    Posts
    17

    Re: OD Chatter On New Citizen L20

    Quote Originally Posted by deadlykitten View Post
    hi nicu / if you are cutting it in one pass + all things you described, i suspect an alignment / rigidity issue

    about the roller feeder i can't help, since i don't have such an equipment; maybe the rollers have a more powerful grip than the collet : did you tried with a shorter bar, that is not clamped by the feeder ?

    about the Z sense : if the guiding bush makes contact among 25mm dinstance, then you can not rough & finish for a Z>25 ( also Z20 may be an issue, because it is too close to 25 )

    the controller allows spindle $1 and spindle $2 to be synced in the Z axis : does this mean that you can clamp with both spindles, and turn something longitudinal ( among Z ) ? i never tried it ...

    how would I turn the end of the part if it's held in the sub-spindle? : depends on real scenario, but, in short : you may go with the 2nd spindle near the end of the part + cut off + continue machining @ 2nd spindle ... just saying; kindly



    In regard to the alignment issue the applications guy indicated the main spindle to the guide bushing and the result was .002" of runout. He called Citizen and he told me that they said that was the upper limit. .002" seems like a lot to me, I thought the upper limit would be .0004", any thoughts? The sub spindle was also off to the guide bushing .002", he performed a grid shift of the sub spindle to compensate. Does it matter if the guide bushing is rotating with the main spindle during indication? I could see if the guide bushing wasn't running true (concentric) to itself, this could be an issue. But what if the guide bushing is concentric does it have to be free from the main spindle turning during indication? Again, it's a brand new machine.

    I haven't ran a short bar yet, good advice though. The interface between the bar feeder and machine won't allow me to leave the bar feeder in manual mode while machining a part, there is a soft key option on the machine controller to disregard the bar feeder but when I select it the machine produces an alarm if I try running a part, any thoughts?

    Thank you for the help and my apologies for the delayed response.

  10. #10
    Join Date
    Jun 2010
    Posts
    4252

    Re: OD Chatter On New Citizen L20

    At this stage I might be wondering whether the brand new machine is 'fit for service'.
    Perhaps the vendor could take it away and only return it when it meets specs?

    Cheers
    Roger

  11. #11
    Join Date
    Jun 2015
    Posts
    4131

    Re: OD Chatter On New Citizen L20

    He called Citizen and he told me that they said that was the upper limit. .002" seems like a lot to me, I thought the upper limit would be .0004", any thoughts : 0.002 is way too much

    The sub spindle was also off to the guide bushing .002", he performed a grid shift of the sub spindle to compensate
    : 0.002 is a real thing, while grid shifting is a only setting; is useless

    Does it matter if the guide bushing is rotating with the main spindle during indication? : of course; i have Citizen L12; guide bushing takes the rotation of the main spindle with the help of a plastic belt : remove that belt

    I could see if the guide bushing wasn't running true (concentric) to itself : if you got 0.002 when spindle & bushing where rotating toghether, imagine what happens when they don't rotate togheter

    But what if the guide bushing is concentric does it have to be free from the main spindle turning during indication? : yup, it must be free :
    ... you slide the indicator inside it among Z
    ... you keep the spindle stationary, put the palpator inside the bushing, and rotate the bushing
    ... now keep the bushing stationary and rotate the spindle
    * you can not proceed without these 3 measumerents; you can not "grid shift" to fix that cnc


    I haven't ran a short bar yet, good advice though : when those 3 determinations are ok, you run a short bar; if it is ok, you check if the feeder is aligned, and you run a long bar


    at this moment there are too many variables; you should take small safe steps i don't know how to disengage your feeder, but is critical to check the cnc without the feeder : it is very possible that the cnc was ok, and that feeder ( with rollers ) to mess up the cnc : imagine what happens if rollers are powerfull and missaligned ( i don't have experience with your type of feeder )

    so, again :
    ... you slide the indicator inside it among Z
    ... you keep the spindle stationary, put the palpator inside the bushing, and rotate the bushing
    ... now keep the bushing stationary and rotate the spindle
    ... when these 3 values are ok, you continue :
    ... machine something using a short bar, that does not reach the feeder ( means checking only the cnc )
    ... check alignment with the feeder
    ... be sure that the feeder is not forcing the spindle or the guide bushing ( such a check is critical )
    ... long bar ( means checking the cnc + feeder )


    that guy that was sent to you, is not well prepared you have some huge errors that are near the upper limit ? that is a non-experienced person







    a while ago i received same answer when aligning a bigger lathe : is ok, is within tolerances, pls look at this papers, you are taking things too serios ?!?! duuuh .... now i can align it, and even more, if it crashed and it is missalinged, i may be able to continue machining without worries

    you have to do it yourself; if possible, try to search for more help arround you, in your area + 400km ( etc ); if you will see how a real experienced person works, you may be able to understand what is she / he doing, only by looking

    find a real experienced person; it would help you a lot / kindly
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  12. #12
    Join Date
    Jun 2015
    Posts
    4131

    Re: OD Chatter On New Citizen L20

    Quote Originally Posted by deadlykitten View Post

    ... you slide the indicator inside it among Z
    ... you keep the spindle stationary, put the palpator inside the bushing, and rotate the bushing
    ... now keep the bushing stationary and rotate the spindle
    ... when these 3 values are ok, you continue :
    ... machine something using a short bar, that does not reach the feeder ( means checking only the cnc )
    ... check alignment with the feeder
    ... be sure that the feeder is not forcing the spindle or the guide bushing ( such a check is critical )
    ... long bar ( means checking the cnc + feeder )
    before you do all those, i would recomand :
    ... check if the collet of spindle 1 is clamping the centro ( coax or interapid ) shank somewhere near the middle of the clamping range; is not critical to clamp the shank concentric to the spindle, but it is critical to avoid clamping it near the begining or the end of the clamping range
    ... remove the centro and put inside the collet an arbor with same dia as the shank : check tir ( tir should be as low as possible, even if the centro does not require low tir )
    ... remove the collet, and check tir inside the spindle
    ... remove the guide bushing
    ... remove that belt that rotates the guide bushing ( you should be able to rotate it by hand, so to check 360* )
    ... now put the collet and the centro back
    ... check concentricity and coaxiality between spindle and guide bushing bore
    ... inspect the guide bushing outside the cnc : it should look smooth, and check od and id to be concentric
    ... put the guide bushing back, and continue with the other steps



    pls share the type of your IEMCA feeder; i wish to search for it, to see how it works; i am interested into how the rollers are clamping the bar, also it is important where the rollers stop, thus to avoid clamping the bar and shifting its position; however, far as i know, those rolers are not touching the bar, thus there it is always clearance / have a nice day Nicu
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  13. #13

    Re: OD Chatter On New Citizen L20

    Is this a L20-XII?

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