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rapix x axis heavy vibration one direction slant bed lathe

Stirling

Hot Rolled
Joined
Dec 11, 2013
Location
Alberta canada
hello,

I am experiencing a heavy vibration when x axis rapids twrards the chuck on my slant bed lathe (modern/microcut lt-65, buffilo machine tools tiwaneese build 20hp).

to deiscribe the vibration i would say it reminds me of spinning up the 8" chuck to 3000 with slightly off balances jaws. not scary, but very obviously present

i have pulled off all sheetmetal that slides with the axis to rule it out, removed the servo to hand spin, no shaft play, typical cogging feeling on the magnetic poles.
the servo does get rather hot if you rapid up and down 20 times, and if i use the machine it errors our under far less load than normal.

using a ratchet to jog the axis with servo removed it is not perfectly smooth. thought it never has been, it does not have a consernable effort to turn, but there is knotchy sections. i cannot see this as a source of significant load or vibration.

linier ways and ball screw look fine.
possible ball screw end bearings?
i have nver replaces a ball screw, is "pre tenisioning" after end bearing changes hard to do?

looking for your thoughts. ive owned it 4 years and not had this issue.
not scared to rip and tear.

thanks!
 
If the x z servos are the same, swap them. might be a pain in the ass but should help you center in on the
issue. My fadal Z going rapid would "bounce" as it rapid z-. z+ no issue. replaced z ball screw and same issue.
swapped y and z and z worked fine. motor/encoder issue.
 
When you had the motor off, did you check for any play in the ballscrew? BTW, not all ballscrews are pre-tensioned. Depends on design.

Also verify your lube lines are not leaking or damaged. Including the ball nut line.
 
thank you all for the tips, i have taken some wooden blocks and pry bars/dial indicator to check for play on the assembly, repectably stiff. all lube lines appar to be intact, running the pump repeatably seems to show adiquate drippage from all lube points.

i will try swapping the servos as i belive they are the same sizem should not be to hard.

i did not think about level, but its worth a quick check!

turning the ball screw by hand felt notchy, cogging. i suspect it is my source of load/vibe/motor oveheat. ball screw looks great, so i suspect a pilot/thrust bearing. shure would be nice to know if there was a pre tension, or how to even check/know in advance?

this may turn into a case of abuse it for a few weeks to complete my production run then really get into dissasmbly the axis if needed. machine wont be needed for a while after i turn off all the parts.
 
Would not hurt if you noted what the POS has for controls and servos (AC? DC? Encoder? Resolver? Tachogenerator? Glass scale on the axis?). Can make a huge difference in deciding what/where to look.

IME, bad thrust bearings do not really make a vibration. Mostly just noisy, poor finish, repeatability troubles, etc.
 
Would not hurt if you noted what the POS has for controls and servos (AC? DC? Encoder? Resolver? Tachogenerator? Glass scale on the axis?). Can make a huge difference in deciding what/where to look.

IME, bad thrust bearings do not really make a vibration. Mostly just noisy, poor finish, repeatability troubles, etc.


controler/servo system is a Fagor 8055 control. AC brushless servo w/ what i assume is a dc rotory encoder (see photo)
I am contacting th encoder manufacturuer for replacment today. if its cheap and not weeks away i may as well. distributor wants an arm and a leg for a new servo :/
swaped bearings in the servo as the stethascope was picking up some minor bearing noise. (Very familiar with motor repair)

I have not noticed a bad finish, though i dont do many long facing cuts to check the X axis, repeatability has ben fine.
if it is the encoder that could def. be a source of hesitaton creating a vibe, which would also ecplain the servo heat buildup

Thnaks!
 

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Maybe look at the servo amp. If something is wacky or failing that could cause what you are seeing. Switch them if not too difficult see if it follows. Maybe retune?


Sent from my iPhone using Tapatalk
 
.....ball screw looks great, so i suspect a pilot/thrust bearing. shure would be nice to know if there was a pre tension, or how to even check/know in advance?

The easiest way to partially determine if your ball screw is stretched is to look in your parts book. A stretchable ball screw will be fixed at both ends. If you have a floating bearing on one end, which is likely opposite the motor end, you obviously cannot stretch anything.

I don't know this with complete confidence, but screw stretching is likely manufacturer specific. My direct experience with it is on Mori Seiki machines. They have a formula for stretch where screw length is part of the formula and it goes from there. They also grind their screws with this stretch in mind. Actually stretching the screw is exacting work. Meaning you have to have all the little ducks perfectly in a row or it's a crap shoot. No guessing and "that should be about right" doesn't do it.

I also can't say for certain if all double fixed ball screws are stretched. A talk with your machine maker about this would be wise. Hopefully the remedy to your problem is simpler then re-mounting a ball screw.
 








 
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