Bad surface finish when facing on Okuma LB15

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fredsal

Plastic

Joined

Aug 4, 2019

• Aug 4, 2019

• #1

Hello all
Recently purchased used Okuma LB15 with OSP7000L control. Running first job and getting terrible finish on face, weather od or bore. Getting circular lines as if I'm running low rpm and high feed rate. I tried running at different rpms, from 300 to 2000, and feeds from .0005 to .01 and no change. Also changed facing tools and boring bars, different inserts and so on, getting same results.

Things to note:
Spindle is loud and has runout of .0006" so I may have a bad bearing. But X axis turns are repeating within .0001"

Is this likely caused by a bad spindle bearing or could it possibly be something else?
Any suggestions would be very helpful
Thanks

 

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Harri89

Cast Iron

Joined

Nov 21, 2016

• Aug 4, 2019

• #2

That runout is quite much imo, should be like half of that or lower. It causes chatter in every machining operation as you say.

Depends ofcourse how and where you measured the runout.


How much movement do you see if you put some 2x4 wood or equivalent under the chuck and try lift it up with a prybar. Mount a diao indicator somewhere in the headstock and the indicator to top of the chuck/spindle

 

Bobw

Diamond

Joined

Feb 8, 2005

Location

Hatch, NM Chile capital of the WORLD

• Aug 4, 2019

• #3

Post a picture..

Bad surface finish can mean a million different things.

 

G

Guest

Guest

• Aug 4, 2019

• #4

Also what type material and what is the size of the part? For all we know you could have a foot of 1" round 6061 hanging out of the chuck.

 

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Vancbiker

Diamond

Joined

Jan 5, 2014

Location

Vancouver, WA. USA

• Aug 4, 2019

• #5

Endplay (axial clearance) in the spindle bearings or dithering Z axis would be my first things to check.

 

litlerob1

Diamond

Joined

Nov 4, 2013

Location

Utah, USA

• Aug 4, 2019

• #6

What type of Tool? How are you holding the Tool and the Material? What is the nomenclature of the Insert?

R

 

O

Other Brother

Hot Rolled

Joined

Dec 6, 2014

• Aug 4, 2019

• #7

You are describing chatter, so what's moving? All of the replies are good ones to check before replacing spindle bearings. That is a box way machine so you need to adjust all of the gibs on every axis according to the maintenance manual. If you still have chatter and have addressed the other replies above you probably have bad spindle bearings.

To check the spindle out remove the chuck and drawtube. Check run-out and deflection on the spindle arbor. Run the spindle and watch the load and see if there is heat building up about 4 inches inside the arbor. The spindle load should be around 10 percent at max rpm. If you see anything above 20 percent load you probably have bad bearings.

Spindle bearings will cost around $4000 for that machine and and down time to repair is normally a week if you find someone that can do the work.

 

F

fredsal

Plastic

Joined

Aug 4, 2019

• Aug 5, 2019

• #8

So, material I'm turning is 1018 steel. 2.25' round stock and .630" thick. Using cnmg to face od and ccmt for id. Tools sticking out no more than .750"
Should not be difficult to get good finish with what I'm cutting. I have done this job before on my Hitachi Seiki and never had any issues, therefore I believe it is something mechanical and not with my parameters.
I tried moving chuck with a prybar and indicator as Harri89 suggested and did not see any movement. My next step will be to check the gibs.
I attached photos so you can see what I am getting. OD and ID is better than 16 micro, but face is more like 125
Why would I get a bad finish only on the face?

 

F

fredsal

Plastic

Joined

Aug 4, 2019

• Aug 5, 2019

• #9

Sorry, meant to add this image as well

 

litlerob1

Diamond

Joined

Nov 4, 2013

Location

Utah, USA

• Aug 5, 2019

• #10

How much stock are you leaving of the face for a Finish pass?

1018 is some horribly gummy junk to machine. I use 1200SFM minimum.

For your part, I would leave .008" on the Face. I would be Facing away from center, or toward center with the Bar. I believe that Lathe max's out at 3k RPM, I would have G50 locked at that. G96S1200 for Roughing and G96S1600 for Finishing on the OD. For the Bore, I would rather have the CSS active than to let it max out, so I would have the G96S500. But leave plenty on the Face. 1018 Finishes way better with tons of RPM and deep cuts.

R

 

F

fredsal

Plastic

Joined

Aug 4, 2019

• Aug 9, 2019

• #11

I tried the parameters you suggested and still getting same results. I am more convinced now that there is something mechanical causing chatter.
I just hate to go and change spindle bearings before knowing what the issue is.

 

DouglasJRizzo

Titanium

Joined

Jun 7, 2011

Location

Ramsey, NJ.

• Aug 9, 2019

• #12

fredsal said:

I tried the parameters you suggested and still getting same results. I am more convinced now that there is something mechanical causing chatter.
I just hate to go and change spindle bearings before knowing what the issue is.

Click to expand...

Do all the indicator checks on the spindle but also, check the turret. If it's been knocked out of line, this can contribute to poor part quality. If it's ok, make sure the clamping is functioning properly. I have the same machine, just a little older, 1983, with an OSP 5000L, it holds tenths to this day.

 

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gregormarwick

Diamond

Joined

Feb 7, 2007

Location

Aberdeen, UK

• Aug 9, 2019

• #13

Dealing with this on one of our victors right now.

First thing to do is verify if there is axial movement on the spindle, indicator on the bed, not the turret.

If so, look up your parts book and check the bearing configuration.

On ours, the spindle is supported on either end by roller bearings, with a double angle pair in the middle. The shell of the double angle pair is spinning in the headstock casting, and moving axially by a couple of thou (the shell retention design is not great IMO), but the rollers are solid. End result is perfect size and finish on turned diameters, grooves and stepping on faces.