PDA

View Full Version : Problem Soliciting comments



Carlton Jenkins
07-05-2008, 09:33 AM
My employer has an Okuma LB15 lathe. The spindle is a bit noisey but I've heard worse. No excessive heat exists. Spindle motor alone with no belts is quiet. Neither new belts nor a gear change affects the sound.

This machine is currently in use but they feel it is not accurate enough for a job they hope to get due to the taper over perhaps 24 to 36 inches.

Operators report a taper of .001 per inch. They also report out of round of about .001 to .003. A single test piece run for me was NOT out of round. With an indicator and a precision ground bar from inspection I found a taper of .0008 per inch. (Most likely taper is not caused by spindle bearings but I'm up against entrenched misconceptions of management and production people.)

The local Okuma distributer (Gosiger) diagnosed bad spindle bearings based upon the noise alone, they used no tools and did no testing. Their quote is $14,700 for the complete job. This machine is roughly 15 years old. Gosiger rebuilt this spindle several years back (before my arrival here) at a price of $9,500.

Previously on Mori-Seiki lathes owned by previous employers I've removed the spindle assembly complete (including cast iron housing) and sent it to Setco, Cincinnati. Setco quotes a rather firm $4,000 to rebuild this one.

Two other local companies want the job but will not quote until they get the spindle apart (which I understand) but my upline is leary of issuing open ended POs.

I would appreciate your observations. Thanks!

69owb
07-05-2008, 10:12 AM
Hi
Just an Idea! Have you checked the level of the machine

neilw20
07-05-2008, 10:48 AM
Is it possible the noise is introduced from the power chuck system, which you no doubt have ?
To check this out reduce the chucking pressure, as well as change from OD chucking to ID chucking and see if this effects the noise. It may be a part of the axial system for actuating the check, and this stuff is not really hard to service once the case is off the headstock area.

As for the taper, I just compensate in the program by adding turning a small taper on purpose that just cancels any error. I have been too lazy to adjust the tailstock !
I can't measure any taper once compensated for by careful adjustment of finish cut.

Carlton Jenkins
07-05-2008, 11:15 AM
Yes, checked level but forgot to mention. Level is good.

RianF
07-05-2008, 03:11 PM
hey there, more than likley you just need a headstock alingment very easy to do by loosening the bolts on the casting around the base of the headstock and jaring it into position( mallet or a 2 by 4 through the spindle). Just leave your indicator on the test bar in the spindle and watch the movment (go slow and run along the test bar after every adjustment).As for the noise it could be the bearings, or the chuck acuator, you could try checking the runout on the acuator to see if its off center...if you know its not the motor then the only way to see if its the bearings is to remove everything else and run it. If you still have noise is probably bearings. See what it feels like also turn very slowly and if it feels graby is most likly bad.

theokumaguy
07-14-2008, 01:06 PM
Carlton,

Could you describe the noise? High pitched whine? Grumbling, gravelly noise? Ticking that is input or output speed dependent?

If the noise is a ticking and has been present/the same for a while, it could be as easy as an oil line bumping a gear/shaft. If this sounds accurate, you can check this by removing the top and front gearbox covers and inspect the position of all the lube lines relative to both the low and high gear shift positions.

Question - when you say gear change does not affect sound do you mean it is the same pitch, or do you mean it is still present but a different pitch? Try low and high gear at similar rpm. If the sound is much higher pitch/louder in low gear at a given speed, and still present but much quieter in high gear at about the same given speed, you could have an input shaft or idler pulley bearing going out. You can diagnose this further if you like by removing the front plate of the headstock and removing the taper pin (along with usually a set screw) that attaches the shifter fork to the shaft. Then move the fork and gear into a neutral position, this will allow you to run the spindle with the control but have no output shaft (spindle bearings) in the mix. Make sure to reinstall the front cover or cover it with cardboard as the oil bath will spray you pretty heavily. Your Run/STM lights will stay on but you can get the machine up to speed and check for noise. If there is no noise, it is in the spindle/gears/workholding assemblies. If the noise is present, and as you stated the motor separately does not make noise, your problem is most likely input shaft, pulleys, alignment of the shifter fork to the gears, or still possibly the motor (noise only under load is rare but possible).

For the taper problem, RianF and neilw20 are both correct. You can program out the taper using taper compensation or fix the problem mechanically via a relatively easy headstock alignment. The hardest part of a headstock alignment truly is the removal of the covers. Remember, on the LB-15 some of the bolts are threaded from below into the headstock, these are located above the spindle motor.

A few questions

If you go to Block Data, in the upper right hand corner do Sr and So match approximately or is there a large variance and constant movement of one of them? If one is moving it could actually be an electrical noise issue (a stretch yes) but possible.

Have you checked the noise from the actuator as described previously? You can also remove the chuck/drawtube assembly and unbolt the actuator from the spindle. Then you can set the actuator on top of a bucket or box next to the machine and run without workholding. This is a little more work, but allows you to completely remove the actuator from the list of possibilities. Just remember to mark the orientation of the actuator before removal and indicate it in when you re-install.