Vibration from boring bars

Meskaroni · Aug 19, 2019

Hey everyone, One of my first posts but long time lurker

in 10+years machining, Ive never felt so defeated.

I am running a small cnc lathe, trying to bore 1-3" diameters.
I have a few 100 programs that ive been running for 5+ years on this machine with these boring bars, perfect finish and sizes.
we hired a new machinist who thought he could save time on my programs so he set the start point to a finished diameter on a 3.5" stock and a 1.5" diameter. so upon finishing the cycle *smash into the piece.

okay, so we aligned the machined with some professionals and all the tool heights are dead on,turret realigned... but unless my boring bars are less than 2" off the turret they vibrate like crazy, 1" thick bars 4-5" deep at the most..

I have tried everything to figure this out and i cant stop the vibration, super slow rpm with heavy cuts, super fast rpm with small cuts, nothing works...

any help would be appreciated sorry for the sloppy post im really busy now that i have to repair these bores on the conventional lathe

Limy Sami · Aug 19, 2019

Maybe silly Q time, but …………

Did the tool holders or where they clamp to the turret get damaged in the crash - or even the turret itself? ……...have you had the tool holder out of the turret and the tools out of the holders?

Delw · Aug 19, 2019

Make sure the head stock is aligned , pull off the chuck or collet nose and check for damage then put it back on.
if the machine ran perfectly before, unless you wiped out the spindle bearings the "professionals" didnt get it correct.

Vancbiker · Aug 19, 2019

Is the machine a Hitachi Seiki by any chance? Some of their models used a cam system to index and clamp the turret. Sometimes a crash would damage that mechanism which left the turret with low clamping pressure resulting in poor cutting performance.

Peter from Holland · Aug 19, 2019

Yes Check your spindle bearings Then the chuck and its jaws
Also the carriage Do you see any movement with a indicator while pulling and pushing at it Same with turret
Peter

Meskaroni · Aug 19, 2019

Limy Sami said:
Maybe silly Q time, but …………

Did the tool holders or where they clamp to the turret get damaged in the crash - or even the turret itself? ……...have you had the tool holder out of the turret and the tools out of the holders?

the smash was with an od tool but i took all the holders off the turret for alignment and also tried multiple holders and positions with the same results.. i am thinking it has to be an alignment issue cause tip of the inserts are chipped after one vibrating pass. but the od tools leave no nipple and cut well and when i scribe across the face with my od tool it lines up perfectly on the bbar

litlerob1 · Aug 19, 2019

My first guess would be the Holders and the mating surfaces to the Turret. Second would be a slightly bent Bar. Third would be the bushings (if you're using them). Fourth would be the Chuck, Jaws, Masters and Hardware.

BTW 5" out with a 1" Bar is too far for conventional wisdom. Sandvik and KM go 3:1 ratio. Personally I'm okay with 4:1. But beyond that, some black magic needs to happen.

R

Meskaroni · Aug 19, 2019

the machine is a kia super turn 21L

I want to pull the chuck off and check but I dont have the drawbar tool..
Ill order one and pull off the chuck, they aligned the turret not the spindle.

what is the best procedure to check my bearings? the manuals are translated from korean or wtv hard to understand and very little info.

Ox · Aug 19, 2019

In all honesty, a boring bar is the least concern for turret alignment.
You can easily mod a bar to seat differently.

In the case of a 1" bar, I'm guessing that you are set-screwing it down?
In that case, you would need to grind your flat a bit different.
But if you could hold it in a collet somehow - you could retard the angle a bit and see what that does.

However - if that tool and holder (and turret position) are not what crashed, and it appears to be all dialed in correctly, then maybe you need to check your clamp somehow, or maybe even if the turret it'self was tightened up?

-------------------------

Think Snow Eh!
Ox

Hoss710 · Aug 19, 2019

I tried replying to this once and it erased it when I went to edit it. I have a KT21. a few things to check. 1 the turret locks up on 2 cam rollers. if its knocked out of timing it can have a soft lockup. to check pull the cover over the turret where the drive gear and belt are. the drive gear should have a alignment mark that aligns with a mark in the shaft. the coupling is meant to slip in a crash scenario. if off realign. second take a 1.5 to 2 inch bar about a foot long. do a skim cut on the OD and measure for taper. next put a indicator in the spindle and jog X in and out across the face of the turret. it should be square to .0005 across the farthest 2 points. let us know what you find.

g-coder05 · Aug 19, 2019

I had the Kia SKT-21 and the SKT21-LMS. Kia/Wia Turrets are weak, and as Hoss710 suggested you need to see if you have a soft or hard lock. The procedure is in that almost useless manual if you can figure out what the little cartoon character is doing but here is a link to a vid that shows alignment and hard lock procedure.

YouTube

Trueturning · Aug 19, 2019

Some torrents have a shear pin in the turret. When it is sheared the torrent will deflect under turning pressure. Something is moving.

Meskaroni · Aug 21, 2019

im aware of all this but im avoiding that method, in the case that im not doing the setup in the futur

DDoug · Aug 21, 2019

Meskaroni said:
im aware of all this but im avoiding that method, in the case that im not doing the setup in the futur

You may not want to, but...

Ya gotta doo what is need to fix the problem.
Period.

Also, did you fire "Mr. Productivity" ?

Meskaroni · Aug 21, 2019

litlerob1 said:
My first guess would be the Holders and the mating surfaces to the Turret. Second would be a slightly bent Bar. Third would be the bushings (if you're using them). Fourth would be the Chuck, Jaws, Masters and Hardware.

BTW 5" out with a 1" Bar is too far for conventional wisdom. Sandvik and KM go 3:1 ratio. Personally I'm okay with 4:1. But beyond that, some black magic needs to happen.

R

5 inches out is the furthest i need, most of my work is 2-3" deep, im having the same issues at 3" but i can shorten the bar and slow down the rpm

thanks for ur input, im confident in my holders and mating, the parts arent running in the spindle with bushings if thats what u meant, and im gonna pull off the chuck as soon as work allows me to check that situation.

i need to bore 10" bushings with a 1.5" id, so i use a 1" bar and do 5" from each side

Meskaroni · Aug 21, 2019

hes actually the best hire ive been able to find in the last few years, but he is milling only now, lol

hes also come to realize how i work, and asks before changing my programs

Hoss710 · Aug 21, 2019

so I'm guessing you didn't pull the cover to check the gear and shaft alignment?

Meskaroni · Dec 5, 2019

Hoss710 said:
so I'm guessing you didn't pull the cover to check the gear and shaft alignment?

sorry, things got a little crazy in the shop over the last few weeks, i changed the shear pins and the alignment is good, im gonna get back into this today, ill double check the gear/shaft alignment and get to the video u posted.

i also took apart the chuck and cleaned everything and got it running withing .001 and still vibrating, today is 1.781" diameter 3.75" deep, running half the sfm and starting to get vibration.

Meskaroni · Dec 5, 2019

@hoss710 i have a taper of .003 over 12" on a 2.5" bar, gonna check the gear/shaft alignment tomorrow morning

litlerob1 · Dec 5, 2019

Meskaroni said:
5 inches out is the furthest i need, most of my work is 2-3" deep, im having the same issues at 3" but i can shorten the bar and slow down the rpm

I'm simply pointing out that a 5-1 ratio is going bounce around. You can explain your reasoning all day, I don't care.

R

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