massive backlash problems!?!?
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    Default massive backlash problems!?!?

    hey guys, got some mad backlash going on in the Z axis on my ST30ATC m/c - i'm talking nearly 1mm of lost motion.

    Here's a video of me hand wheeling 1mm... (after going 1mm+ setting indicator then 1mm-)

    Shared album - Travis Hammond - Google Photos

    Clearly not ideal! where should I start looking? could this be as simple as a thrust washer issue (ball screw turning but not transferring the force)

    I'm also able to rotate the ball screw a very small amount by hand, is this also no bueno?

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    Have you checked for endfloat on the ballscrew? Could be a thrust bearing gone. Is it noisy in rapid?

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    Quote Originally Posted by sudsy55 View Post
    Have you checked for endfloat on the ballscrew? Could be a thrust bearing gone. Is it noisy in rapid?
    I haven't and I also don't know how to massive backlash problems!?!? it's not exceptionally noisy, but I'll do some more listening now the shitty old guard are disconnected.

    Sent from my G8141 using Tapatalk

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    Quote Originally Posted by xa-mont View Post
    I haven't and I also don't know how to massive backlash problems!?!? it's not exceptionally noisy, but I'll do some more listening now the shitty old guard are disconnected.

    Sent from my G8141 using Tapatalk
    what dial indicator is touching? Turret? What is happening when you move Z axis? NC send a command to SERVO MOTOR, motor rotates and through coupling rotates ball screw, ball screw nut is attached to the carriage (never seen ball screw nut bad on any MAzaks in whole my life). Carriage has two rails (x asis) with GIBS that needs to be adjusted periodically , as it is not linear bearings. Then after this, rails movement( more like X rails gap) passed to turret itself.

    if that is not overcompensation of Z axis backlash through NC parameter, than it would be gibs that must be adjusted , to compensate X-axis rails wear.

    by the way, your dial is 10 micron division, jumping around 6 *10=60 microns. That is quite normal for this
    pile of casting, hardened steal and old Mitsubishi electronics. Buy a beer and take it easy for now, or adjust gibs on X-axis rails . =)

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    Quote Originally Posted by noname777 View Post
    what dial indicator is touching? Turret? What is happening when you move Z axis? NC send a command to SERVO MOTOR, motor rotates and through coupling rotates ball screw, ball screw nut is attached to the carriage (never seen ball screw nut bad on any MAzaks in whole my life). Carriage has two rails (x asis) with GIBS that needs to be adjusted periodically , as it is not linear bearings. Then after this, rails movement( more like X rails gap) passed to turret itself.

    if that is not overcompensation of Z axis backlash through NC parameter, than it would be gibs that must be adjusted , to compensate X-axis rails wear.

    by the way, your dial is 10 micron division, jumping around 6 *10=60 microns. That is quite normal for this
    pile of casting, hardened steal and old Mitsubishi electronics. Buy a beer and take it easy for now, or adjust gibs on X-axis rails . =)
    I think you're miss interpreting the video a bit. The dial is indicating .06mm of movement (or 60 micron as you said) however that's when I have manually jogged the machine 1mm (or 1000 micron) so you can see the issue.

    The dial in the video is pushing against the X axis way, so there's no way the X axis can have anything to do with this issue.

    Sent from my G8141 using Tapatalk

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    probably let me see it again
    i dont get it , honestly.
    can you write it down step by step what you do.
    and what Z-axis numbers on POSITION screen are doing at this particular time

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    Quote Originally Posted by noname777 View Post
    probably let me see it again
    i dont get it , honestly.
    can you write it down step by step what you do.
    and what Z-axis numbers on POSITION screen are doing at this particular time
    1 - machine set in hand wheel mode at .1mm per pulse
    2 - jog machine to the right 1mm
    3 - set indicator up on x axis way and zero
    4 - jog 1mm right again
    5 - jog 1mm left (to presumably if nothing is wrong land the indicator back on 0)
    6 - indicator is nowhere near 0 - this is where the video starts.
    7 - jog 1mm right again - this is what can be seen in the video - the controller is indicating 1mm of movement - the indicator, as you pointed out, is indicating .06mm of ACTUAL movement.

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    First question is WHAT does the indicator read at step 6? If not 60 Micron, what is the reading? Nowhere near 0 is not helpful at all.

    The important missing info is any history of the "problem"
    Is this a new to you machine with this problem?
    is the result of a recent crash?
    Or things were working well and this just started?
    What is the backlash setting?
    Have you made any changes to the backlash parameter?

    I would use an indicator with longer travel and lower resolution and see what you have for problems over 10mm travel.
    Also check again 500mm away and see what you have.

    Since you don't know how to check for end float in the ballscrew, I would find out how before messing with parameters.

    Bill

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    Quote Originally Posted by hitandmiss View Post
    First question is WHAT does the indicator read at step 6? If not 60 Micron, what is the reading? Nowhere near 0 is not helpful at all.

    The important missing info is any history of the "problem"
    Is this a new to you machine with this problem?
    is the result of a recent crash?
    Or things were working well and this just started?
    What is the backlash setting?
    Have you made any changes to the backlash parameter?

    I would use an indicator with longer travel and lower resolution and see what you have for problems over 10mm travel.
    Also check again 500mm away and see what you have.

    Since you don't know how to check for end float in the ballscrew, I would find out how before messing with parameters.

    Bill
    The reading can be seen in the video - it's .22mm off hitting back on 0

    I didn't include history because most of the regulars in this section already know the history, but long story short:
    I bought the machine second hand recently in an unpowered state site unseen. With the help of people here I got the batteries changed, parameters loaded, tool holder realigned (not your standard turret alignment procedure) and a few other little bugs sorted out.
    I've been making parts on it for the last few months and hadn't noticed any z axis issues until Friday (when I posted) this may have just been due to not running anything that made it obvious.

    Sally I don't currently have a longer travel lower res indicator, but I've ordered a 50mm travel .001 one.

    Don't get me wrong, I understand the idea of end float on a ball screw, but I'm sure there are some intricacies to measuring it on such a best that I hope someone will enlighten me on.

    Sent from my G8141 using Tapatalk

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    I've added another video to the shared album (ST30ATC M/C z axis backlash - Google Photos) - what can be seen here is the mag base mounted on the x axis way and the stylis on the flank (i guess that would be the term for it - the "wall" of the thread) of the ball screw thread and jogging back and forth. To me this would indicate ~.12mm of consistent backlash in the interface from the ball screw to the ball nut.

    I've also included a photo of the tail end of the ball screw assembly - I assume being a capped design there will be a thrust bearing held in by that cap? (sadly i don't have a parts drawing for this machine.)

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    First I would clean machine up a bit. with the head centered in middle of travel Then I would set up another indicator on the end of the ball screw then with a bottle jack and a 4 x 4 wood between the head and table pump slowly and check for backlash lost motion and se if its a bad ball nut or thrust bearing, Then move it to the top of travel and do it again. If the screw moves then you know the bearings are loose. They should be tight and sometimes we stretch the screw a few tenths after it is no backlash. I would also suspect the nut / screw is bad and has backlash from the looks of how filthy it is. also move the zee down all the way and use a mirror and flashlight (torch, what they call them in uk) a
    nd look at the ball screw and see if there is a wear grove on the threads. If there is a groove you will bed to replace the screw / nut assembly or have it repacked with larger balls.

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    Quote Originally Posted by Richard King View Post
    First I would clean machine up a bit. with the head centered in middle of travel Then I would set up another indicator on the end of the ball screw then with a bottle jack and a 4 x 4 wood between the head and table pump slowly and check for backlash lost motion and se if its a bad ball nut or thrust bearing, Then move it to the top of travel and do it again. If the screw moves then you know the bearings are loose. They should be tight and sometimes we stretch the screw a few tenths after it is no backlash. I would also suspect the nut / screw is bad and has backlash from the looks of how filthy it is. also move the zee down all the way and use a mirror and flashlight (torch, what they call them in uk) a
    nd look at the ball screw and see if there is a wear grove on the threads. If there is a groove you will bed to replace the screw / nut assembly or have it repacked with larger balls.
    There's no table on this bad boy Richard - it's a lathe.

    I think I can conclusively say the thrust bearing is the culprit - here's a video (in the shared album again) at the motor end with the z axis being jogged back and forth. BULK movement. it would be super handy if i had a parts drawing for this machine though so i can see what bearing arrangement they have.

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    I suppose I should have looked up the model number...but the procedure is about the same.

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    I'll have a look at my manuals tomorrow and see if I have anything useful for you

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    There looks like a lot of movement in the last video switching from in/out. Parts drawing would help...I agree. Snugging up the Z-gibbs wouldn't hurt if you haven't tried already, it might indeed help. (Stranger things have happened).

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    Quote Originally Posted by xa-mont View Post
    hey guys, got some mad backlash going on in the Z axis on my ST30ATC m/c - i'm talking nearly 1mm of lost motion.

    Here's a video of me hand wheeling 1mm... (after going 1mm+ setting indicator then 1mm-)

    Shared album - Travis Hammond - Google Photos

    Clearly not ideal! where should I start looking? could this be as simple as a thrust washer issue (ball screw turning but not transferring the force)

    I'm also able to rotate the ball screw a very small amount by hand, is this also no bueno?
    It look likes your thrust bearings is bad. The ball nut also seems to have way to much motion.

    Do you have a lubrication problem?

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    Quote Originally Posted by Ziggy2 View Post
    It look likes your thrust bearings is bad. The ball nut also seems to have way to much motion.

    Do you have a lubrication problem?
    i don't THINK i have a lubrication problem. the way this ballnut (and the x i assume from the noise) is lubricated is from an air purge with an oiler in line, and there's definitely air coming out, and the most used part of the z ballscrew has definitely had oil on it. I suspect it could do with a bit more though, which may be down to the air pressure being either to high or low, not sure.

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    Quote Originally Posted by xa-mont View Post
    i don't THINK i have a lubrication problem. the way this ballnut (and the x i assume from the noise) is lubricated is from an air purge with an oiler in line, and there's definitely air coming out, and the most used part of the z ballscrew has definitely had oil on it. I suspect it could do with a bit more though, which may be down to the air pressure being either to high or low, not sure.
    How much oil is going through the lubricator. Blowing air only tells us that the air is working not how much oil.

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    so... i found a thing... and i feel like a knob... i expect everyone should remind me of this constantly.

    i was removing the bearing cap on the tail end bearing housing to check out the thrust bearing and see if it exploded out in a mess of bearings/cage when i opened it, and it was then that i noticed. the rear bearing housing was loose AF! like the bolts weren't even finger tight!

    I tightened that bad boy up - took some measurements - messed with the BL parameter and here we are...

    https://photos.google.com/share/AF1Q...gtOExHUUtrT3l3

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    Quote Originally Posted by Ziggy2 View Post
    How much oil is going through the lubricator. Blowing air only tells us that the air is working not how much oil.
    i pulled the lubricator apart because there wasn't any obvious "mist" coming from it. gave it a clean and now it's misting nicely. anyone know how much oil (ish) i should be going through per hour on it (or some other quantifiable measurement) or what air pressure i should be running to/out of the oiler? again, not having manuals makes it difficult to know.


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