[joe-w]

When I work at the slender pin which is as shown in the picture, I got chatter. I decreased rpm to 800 to eliminate chatter but the inserts wore fast. The material is Stainless Steel 309 and the parts are in a batch of more than 300. I can't afford one insert just for a few pieces.
Could anybody help me? Thanks

[txcncman]

Are you absolutely sure your tool tip is exactly on center line? Have you tried leaving less than 0.005 per side for a finish pass at low rpm after roughing at higher rpm?

[joe-w]

Are you absolutely sure your tool tip is exactly on center line? Have you tried leaving less than 0.005 per side for a finish pass at low rpm after roughing at higher rpm?

Thank you for help
I set the tool tip by probe.
I left 0.005 in diameter for finishing. And when i increased rpm to 1050 to rough, the chatter arose.

[KenFoulks]

Post more parameters/g-code/pics. How much of the part is in the chuck jaws? Where are you in relation to the insert manufacturer's spec? Have you tried using SSV?

[txcncman]

When you say "set the tool tip by probe" I assume you mean you set the tool geometry offset with the setting probe in the machine. This has nothing to do with the tip of the tool actually being on the center line (Y axis) of the part.

To check a tool tip center line, use that tool to face a piece of material. When the tool reaches X-0.032 is there still a nipple on the face of the part? If yes, the tool is not on center line (Y axis). Re-align the machine or have a machine mechanic come do it for you.

As a work around, you can adjust the tool by shimming the tool holder (or machining the tool holder) as needed. (This is why machinists need to know how to run a manual lathe before getting into CNC.)

I did not understand when you say "when i increased rpm to 1050 to rough, the chatter arose". Do you mean chatter increased? Or do you mean chatter stopped?

If none of the above is working for you. My final solution would be to rough and finish the 0.290 diameter first to the 0.375 dimension. Then machine the 0.375 diameter, rough and finish. This leaves the maximum support on your bar stock at the greatest length possible while machining.

[djr76]

try leaving a larger finish allowance and increasing your feed rate on finish pass. With the right insert, you should be able to do that at 2500 rpm or more with a .05 per pass at .01 ipm. To what txcncman has explained by shimming, I have to shim all my holders for correct center line.

[txcncman]

On shimming/trimming tool holders: This is something that you should not have to do in a perfect world. But a lathe can become misaligned for different reasons. General wear from use. Crashes. Settling. Ideally you want to put the machine back into the correct alignment. By doing so it not only will solve tool alignment problems, it will let the machine cut better, less chatter, and more accurately. If you do not know how to align your particular lathe, call in a machine mechanic to do it for you. Yes, mechanics can be costly. The ones I deal with charge $125.00 per hour. But a good mechanic can re-align a machine in about 3 hours. How much will that $450 spent now save you in time and headaches and scrapped parts in say the next 6 months? Unless a machine seems to be cutting perfectly, I tend to want to re-align them about once per year. More often if they have been crashed.

[joe-w]

Post more parameters/g-code/pics. How much of the part is in the chuck jaws? Where are you in relation to the insert manufacturer's spec? Have you tried using SSV?

There are more than 2 inches in the jaws.

And What's mean of SSV?

Thank you, Ken

[joe-w]

When you say "set the tool tip by probe" I assume you mean you set the tool geometry offset with the setting probe in the machine. This has nothing to do with the tip of the tool actually being on the center line (Y axis) of the part.

To check a tool tip center line, use that tool to face a piece of material. When the tool reaches X-0.032 is there still a nipple on the face of the part? If yes, the tool is not on center line (Y axis). Re-align the machine or have a machine mechanic come do it for you.

As a work around, you can adjust the tool by shimming the tool holder (or machining the tool holder) as needed. (This is why machinists need to know how to run a manual lathe before getting into CNC.)

I did not understand when you say "when i increased rpm to 1050 to rough, the chatter arose". Do you mean chatter increased? Or do you mean chatter stopped?

If none of the above is working for you. My final solution would be to rough and finish the 0.290 diameter first to the 0.375 dimension. Then machine the 0.375 diameter, rough and finish. This leaves the maximum support on your bar stock at the greatest length possible while machining.

Thank you, txcncman

I faced to X-0.032 by roughing and finishing tool, and there is nothing left.

I mean when I was turning at rpm less than 1000, there is almost no chatter. but when I increased the rpm to 1050, there is heavy chatter.

[joe-w]

try leaving a larger finish allowance and increasing your feed rate on finish pass. With the right insert, you should be able to do that at 2500 rpm or more with a .05 per pass at .01 ipm. To what txcncman has explained by shimming, I have to shim all my holders for correct center line.

Thank you, djr76

I will do that if I find the tips are offset

[joe-w]

here are some pic I took by phone.

Please have a look at the flat end, That is another trouble. I machined it by live tooling(5/8 endmill), the heavy chatter damaged the cutting edge just a few pieces. I have tried rpm 3000, 2500, 2000,1500 and 500. feedrate is 0.002/tooth.

[joe-w]

On shimming/trimming tool holders: This is something that you should not have to do in a perfect world. But a lathe can become misaligned for different reasons. General wear from use. Crashes. Settling. Ideally you want to put the machine back into the correct alignment. By doing so it not only will solve tool alignment problems, it will let the machine cut better, less chatter, and more accurately. If you do not know how to align your particular lathe, call in a machine mechanic to do it for you. Yes, mechanics can be costly. The ones I deal with charge $125.00 per hour. But a good mechanic can re-align a machine in about 3 hours. How much will that $450 spent now save you in time and headaches and scrapped parts in say the next 6 months? Unless a machine seems to be cutting perfectly, I tend to want to re-align them about once per year. More often if they have been crashed.

Thank you txcncman,
You are right. I will do that once there is tool alignment problems.

[djr76]

here are some pic I took by phone.

Please have a look at the flat end, That is another trouble. I machined it by live tooling(5/8 endmill), the heavy chatter damaged the cutting edge just a few pieces. I have tried rpm 3000, 2500, 2000,1500 and 500. feedrate is 0.002/tooth.

you can do it 1st before turning while you have 1/2" stock to give it rigidity, downside is you will have some interrupted cut, but a good quality roughing insert shouldn't be phased by it. Or you can do it with 2 end mills, a rougher then a small diameter for finish after turning.

[txcncman]

Wow. You been working on this problem 2 days and still do not have 300 good parts finished? Should have been dropping them off the machine completed at a rate of about 20 per hour. I feel bad for ya. Good luck.

[KenFoulks]

There are more than 2 inches in the jaws.

And What's mean of SSV?

Thank you, Ken

SSV is Spindle Speed Variation:

How To: Spindle Speed Variation | Haas

[joe-w]

Wow. You been working on this problem 2 days and still do not have 300 good parts finished? Should have been dropping them off the machine completed at a rate of about 20 per hour. I feel bad for ya. Good luck.

Thank you

[joe-w]

you can do it 1st before turning while you have 1/2" stock to give it rigidity, downside is you will have some interrupted cut, but a good quality roughing insert shouldn't be phased by it. Or you can do it with 2 end mills, a rougher then a small diameter for finish after turning.

Thank you djr76