What are the main reasons of why this would happen?

[EyeEmTrash]

Below is a picture of a part I have made a few times. I have had this problem before but I can't remember what I did to fix it. I think I changed finishing tools. The machine was just fixed so some of the tools may have gotten mixed up. When I use a certain tool this (the picture below) happens but I think last time when I used a different finishing tool, no problem. That would lead me to believe it would have something to do with the radius of the insert but I don't understand why. I may be misremembering how I solved the problem last time.

I am running the finish cut at a depth of .01 and a feed of .003. The picture below shows the bottom of the part. The OD is 3.25 and the ID is 3.025. They both taper towards the top, the OD gets bigger and the ID gets smaller. There is a big radius at the bottom as you can see, its .500. The chuck is at a low pressure as to not crush the top. All that is being done at this point is turning it down to size. What could be the issue? Just to add, I know when this is happening because I hear a noise. I don't know how to exactly describe it. It's like a mix of someone vacuuming in another room and a ringing in your ear. Vibration? Help?

 

[13engines]

What is the material and length sticking out of the chuck?

That cut depth and feed seem a little on the small side.

Mostly it looks like you need a more positive insert.

I had that same look yesterday on some steel bar that was being turned down to 0.985 from 1 inch, but the stock was so far undersized that it was barely cutting anything. And more often then not, not cleaning up. I switched to a positive insert and fixed it.

 

[Nerdlinger]

What are the RPM’s and what insert(s) are you using? A smaller nose radius would be better because it would put less pressure on the part and thusly less likely to cause the chatter you are seeing.

 

[Scruffy887]

Below is a picture of a part I have made a few times. I have had this problem before but I can't remember what I did to fix it. I think I changed finishing tools. The machine was just fixed so some of the tools may have gotten mixed up. When I use a certain tool this (the picture below) happens but I think last time when I used a different finishing tool, no problem. That would lead me to believe it would have something to do with the radius of the insert but I don't understand why. I may be misremembering how I solved the problem last time.

I am running the finish cut at a depth of .01 and a feed of .003. The picture below shows the bottom of the part. The OD is 3.25 and the ID is 3.025. They both taper towards the top, the OD gets bigger and the ID gets smaller. There is a big radius at the bottom as you can see, its .500. The chuck is at a low pressure as to not crush the top. All that is being done at this point is turning it down to size. What could be the issue? Just to add, I know when this is happening because I hear a noise. I don't know how to exactly describe it. It's like a mix of someone vacuuming in another room and a ringing in your ear. Vibration? Help?

View attachment 432722

WTF, does your SETUP SHEET indicate to use "a certain tool"? Without saying what that "certain tool" was? And no mention of what material you are turning. I turn tons of Acetal and every once in a while some comes through with perfect specs, turns like sticky poo poo.

 

[Northman Ind.]

try a higher rake, uncoated insert, or possibly a smaller nose radius, maybe a bigger radius? or higher feed rate slower spindle speed.

 

[TeachMePlease]

Hold your tongue on the other side of your mouth during the finish pass.

 

[plastikdreams]

Hold your tongue on the other side of your mouth during the finish pass.

This...

 

[eKretz]

Hoo boy. How long have you been running machine tools? I very much hope you're new to this.

 

[EKrol]

Sharp uncoated tool (aluminium). Lower rpm, higher feedrate and deeper cutdepth. Work closer to the Chuck if possible. If you machine has rpm fluctuation function use that also. Smaller radius tool. 0.4mm is perfect.

 

[Scruffy887]

Maybe butt plug grade plastic because the finish looks like s....
Very sharp tool and 0 rake. Not too hard to whip up a HSS bit holder and grind one for your lathe. Positive rake will pull the part into the cutter, negative will push it away. O rake and maybe a spring pass.

 

[EyeEmTrash]

Hoo boy. How long have you been running machine tools? I very much hope you're new to this.

I'm not that new. Still learning though.

 

[EyeEmTrash]

Sharp uncoated tool (aluminium). Lower rpm, higher feedrate and deeper cutdepth. Work closer to the Chuck if possible. If you machine has rpm fluctuation function use that also. Smaller radius tool. 0.4mm is perfect.

Unfortunately I cant go closer to the chuck. The insert I was using was .015 (.4mm), by RPM fluctuation are you talking about G97? I am using that if that's what you mean?

 

[EyeEmTrash]

Hold your tongue on the other side of your mouth during the finish pass.

Forgive me but I don't know how that helps me.

 

[EyeEmTrash]

try a higher rake, uncoated insert, or possibly a smaller nose radius, maybe a bigger radius? or higher feed rate slower spindle speed.

Yeah I'm going to try all of that. Was just hoping to get a definite answer before I played around. Will do though. Thanks

 

[EyeEmTrash]

What are the RPM’s and what insert(s) are you using? A smaller nose radius would be better because it would put less pressure on the part and thusly less likely to cause the chatter you are seeing.

The one that made the part like that was .015, RPM 1500.

 

[EyeEmTrash]

What is the material and length sticking out of the chuck?

That cut depth and feed seem a little on the small side.

Mostly it looks like you need a more positive insert.

I had that same look yesterday on some steel bar that was being turned down to 0.985 from 1 inch, but the stock was so far undersized that it was barely cutting anything. And more often then not, not cleaning up. I switched to a positive insert and fixed it.

Nylon, sticking out around 8 inches, not much of a choice on that end.

 

[eKretz]

I'm not that new. Still learning though.

You don't recognize chatter? Pretty noob level stuff there. It's not at all surprising that your part is chattering with 8" stickout at ~3" diameter and under 1/8" wall thickness. You've already been given the steps to take to solve the problem by others.

 

[Crowne]

Just to add, I know when this is happening because I hear a noise. I don't know how to exactly describe it. It's like a mix of someone vacuuming in another room and a ringing in your ear. Vibration? Help?

For your information, this is what we call chatter.

EDIT: Ah, eKretz just beat me to it.

In this specific case, it's your workpiece that is oscillating harmonically and inducing the wavy pattern you see. Other times, it's the tool that suffers from these oscillations. If you're unlucky, it's both at the same time!

 

[EyeEmTrash]

You don't recognize chatter? Pretty noob level stuff there. It's not at all surprising that your part is chattering with 8" stickout at ~3" diameter and under 1/8" wall thickness. You've already been given the steps to take to solve the problem by others.

I just don’t understand why you’re so grumpy about it. I’m on my own for the first time so I have to problem solve some things that I’m not used to. So that’s why I come here on this forum. I thought it was for people to help people, even clueless people like me. It’s called chatter, ok got it. Won’t make that mistake again.

 

[EyeEmTrash]

Thanks for all the help guys. I took a couple of test cuts on the old piece with a turning tool I found buried. It has a more positive rake, I guess it’s called. I never had a problem with having to use certain shaped inserts before but now I have. Thanks again.