Waviness in the finish, what causes it and other questions.

Hi guys,

I had to enhance this picture to show the problem as it's actually quite faint. It's not just me, I have noticed it in many other people's finishes, usually when cutting thick pieces. In my case I was cutting (contouring) 15mm plate with an 8mm endmill and it only happens at the start of long pieces, i.e. when the milling machine bed is furthest from its centre, then it soon disappears along the line when the bed starts to travel closer to the centre. What can cause this waviness?

Attachment 22495

Second question. Cutting noises: do you have some video link where one can hear what "chatter" actually sounds like?

I have experienced what I think I would call "resonance", but maybe this is what you call "chatter". For example, when squaring the edge end of 40mm extrusion using a long 12mm endmill, you get this unbearable and continuous high pitch shrill noise that can sometimes be reduced a little by trying different motor revs, usually reducing revs, or increasing feed rate, I think. Similar noise sometimes when parting off on the lathe some distance away from the chuck.

So if this high frequency noise is what you call chatter, how does it differ from resonance?

Many thanks.

Edward

OK, in search for an answer, I've found some youtube videos that illustrate typical examples of chatter.

https://www.youtube.com/watch?v=LTIEXLE9dH8
https://www.youtube.com/watch?v=U74NzmPrzeo
https://www.youtube.com/watch?v=QaIVvd2wFOM

As said above, I've only experienced that kind of high frequency nasty chatter noise when squaring the end side of 40mm extrusions, which is understandable, due to the vibration of the unsupported inner shape of the profile, and maybe deflection of the long endmill needed to machine this.

I've also seen videos of how chatter can affect the finish, kind of curly marks on the surface. But my initial post above with the photo of the wavy surface pattern seems different in shape, as these are vertical spaced lines. I certainly didn't hear any chatter when cutting, but perhaps there was some sort of vibration or lack of rigidity?
Any clues please?


Edward

Could perhaps be slightly flex/bounce under rapid acceleration or deceleration as it approaches the edge?

Try with some really gentle accel/decel figures and see if you get the same effect perhaps?

What machine is it?

Hi Zeeflyboy,

You could well be right, the sudden impact... I must say that I always set the Fusion360 lead-in lead-out feed rates the same as the cutting feed rate as I've seen no difference under normal circumstances. I can also try the accel/decel settings in the controller, see if it helps. These were light fast rate passes on an SX3 milling machine, which otherwise gives me a very nice finish. I need to get to the bottom of this. Thanks.

Edward