F&%$ing Chatter

[Wino1442]

Hi all....being fairly new at machining I come to you seeking knowledge from all who have been at this for way longer than I. I wanted to turn a 6 -1/2" long x 1- 1/2" piece of 1045 between centers, but got terrible chatter. I was using a lathe dog and placed a counterweight on the faceplate.....didn't help. Tried different speeds and different tools (HSS & inserts) still didn't help. Then I chucked it up in the 4-jaw, dialed it in, and used a live center and still no improvement (tried different speeds and tools as before ). I finally put the 3-jaw back on the machine with the live center and finally, after trying an insert that is for aluminum I got a chatter free cut (although I think the finish could be a little better).
My question is this: In situations like this is there some trick to getting no chatter or is it just a trial and error type of thing. I just found it unbelievable that I was getting chatter on a 6 1/2" long work piece. I didn't think that was too long or so long that I would get chatter the way I did. Any advice you all could give me would be greatly appreciated. Thanks

 

[ttabbal]

Chatter seems to be mostly about rigidity. What kind of lathe are you working on? What was the RPM and DOC?

That you got rid of it with an aluminum insert kind of backs that up. Those are honed sharp and would have reduced tool pressure compared to a normal insert tool. How it compares to HSS depends on the grind and how well honed it is.

Could it have been hardened either as supplied or through work hardening?

 

[mikey]

First off, 1045 is a medium carbon steel with a machinability rating of 64% so it is on the harder side. Not sure what kind of lathe you have but harder materials like 1045 and 4140 have similar machinability ratings and do better on larger, more rigid machines.

Second, turning between center is an accurate way to turn but it is the least rigid of all methods of work holding. Not the best choice when machining a material that is already half-hard. A jawed chuck and live center is the way to go.

Third, the length of the work piece has little to do with chatter. Chatter has more to do with feeds and speeds and you didn't mention your speeds. Regardless of the cutter type, the rule of thumb when you encounter chatter is to reduce speed, increase feed or both. Depending on your tool geometry, reducing the lead angle of your tool will also help.

Fourth, depths of cut matter. If you encounter chatter, try reducing your depth of cut a bit. What the material is telling you is that something is too ambitious and one of those can be your depth of cut. Back off on your depth of cut, slow the lathe down and increase feed a bit and I bet things will work better.

Finally, tool type matters. It influences your speeds, feed and depths of cut. You mentioned that the lathe cut better with an insert intended for aluminum. I assume it is an AK insert. These inserts typically have ground edges and very positive rake. Therefore, they tend to lower cutting forces, which is a good thing. You didn't mention your nose radius and that also impacts on chatter; the bigger the nose radius, the more rigid and powerful the lathe needs to be.

Lots of things cause chatter. Give us more info and we can maybe give you better advice.