Hi Everyone,

I have started a job, and it went so well to start, but now the boring bar will not stop chattering. We tried changing the insert first, then moved on the speed and feed changes. We even tried changing the depth of cut to no avail.

Thanks

:confused:

If it would help, I could download pics of the parts.

If possible shorten the lenght that the tool sticks out and use a positive type insert. General rule of thumb tool stick out less than 4* dia of said tool.

P.S. spindle bearings can play a big part.

Please post pics of Job and set up and materail type.

John

This boring bar, is it in a turning center or a machining center?
A little more information could be helpful.
What kind of material etc etc...Regards Walt

Sorry guys,

The material is 4130 steel. It is on a lathe and it is as short as it can be already.

Pics to follow soon.

can it be a bigger tool? and how thin a wall is the part?

Try boring from the inside out to try and get under the chatter also an old trick to stop vibration is to wrap the boring bar with elastic bands . Helps absorb the vibration , next step carbide bar.

try some thick tapping oil , rather than flood coolant ,if that's what you are using , maybe try using a used insert that is in decent shape , sometimes a new insert will chatter until it has some wear on it

Insert will need a very small nose radius to reduce cutter pressure - say .007 - .015"

Use a positive insert with minimum corner, wrap boring bar and part with rubber bands slow RPM

is the tool on center? how big is the hole you are boring? are you using the largest size boring bar possible? it can be a number of things.

having problems posting pics.

The question has more to do with the fact that the first 15 pcs were perfect. Without changing anything, the chatter suddenly became a problem from one piece to the next. Now we can't get rid of it.

Ah,
I to have run into this situation before on bar stock turnered out to be the material was a little difrent in the mid of the bar stock than on the ends go fiquire like to drove me nutttsssss!!! It could be a chemical dif or mechanical like its ben work hardend. I would try a slighty higher feed rate and or more depth of cut to keep the tool loaded. Also what type of tool (insert) are you using (I.E. CNMG 431, CCGX 430 exc.) pluss lead angle of. Oh and material condition.

Oh ahh is this a first op or 2nd and or 3rd? just asking cause I have seen parts change by diffrent ops, you know one guy may be more agressive than the other and or vis/versa just a thought.

John

Did the chatter start when you began using material cut from a different bar? I have had a similar thing happen with leaded steel and my conclusion was that one bar was slightly different. maybe a little bit harder or something, tool deflection also changed and sizes changed.

attach some lead wheel balancing wieghts to the back of the boring bar as close to the tip as possable. use hose clamps to secure the whieghts if the hole size allows or masking tape if hole is close to the bar.

What kind of tool mount system is used on this lathe?

What diameter bar?

What insert are you using?

Thanks for all your help guys.
Sorry I have not replied in so long, but I was very bussy with these jobs.
We have found that there is probably the material being different with every bar like was mentioned. Apperantly, the tolerances for the ingredients of materials is quite loose, so they vary.

Not suprising......
last placed I worked we had parts we had been making for years...never a problem. Then we had a batch that had all kinds of issues, finish,warping after cuts, holding size, etc. Turns out even though we bought material, (2024-T4) from same supplier as always we hadn;t specified "Domestic". They substituted "Offshore". Even though it was certified & met all chemicals & properties the variences caused the above referenced issue. It is why when at all possible I specifiy "Domestic" material. Why cause myself grief.

I don't know how much room you have to work with, but a set of vise grips clamped onto the back of the bar does wonders.

Sometimes a good way getting vibration marks off the part is using low rpm and much higher feed.

Been a long time since I operated a lathe or CNC machning centre, 20 odd years since I left the trade, but I recall we used to use all of the above methods and also lifting the bar slightly above centre sometimes helped.

lots of good advice. some We tried already and some new.
The biggest mistery of the job was why it worked perfect for the first 30 odd pieces and not all.
We are looking into the material certs to find differences but in the mean time, we will try some of the tricks of the trade learned here.

Does the boring bar have been removed, manipulated, drop on the floor after the first 30 pieces? A trick that I use sometime when all tricks metionned above doesn't work is to take a honing stone and rub it on the corner radius of the insert to dressed the clearance angle a bit. It will round a bit the cutting edge which in some case does miracle with chattering issue.