[coffeetek]

Hi Guys,

I have this problem that I have not been able to figure out how to fix. Whenever I am cutting on Y axis regardless of end mill type or end mill size I use and regardless of tool holder I get this really bad chatter. Feeds and speeds don't matter much either. The only way I found to reduce it a bit is to go deeper with the cut and faster, but even then it does not cure it 100%. Something is wrong. At first I thought that perhaps X gib is loose but after adjusting that nothing has changed...


Same exact cut while moving X axis leaves very nice surface finish. See attached images. This was contoured in one pass. While cutting on Y, crazy chatter, cutting on X looks good. Same feeds and speeds same width of cut, same depth of cut. Y chatters, X does not.


Anyone have any suggestions?

[Jim Dawson]

If you didn't have pictures of it, I would say that pattern is impossible. I've never seen anything like that.

What end mill are you using?

[CitizenOfDreams]

As if the G-code already has a meander in it instead of a straight line...

[LeeWay]

That is not what I see when I see a chatter pattern. That looks like timing gears or something.
Does it sound bad when it is doing this?

[coffeetek]

End mill does not matter, I use Lakeshore Carbide and Destiny tool. Both do it. 1/4, 3/8 or 1/2 does not matter they all do it. Its got to be a problem with the machine.

Yes that is straight line movement on Y axis. Does not sound bad when it does it. Something is loose on machine I think I just don't know what it is.

Yesterday I was playing with it and I got it to mostly stop doing this by taking heavier cut at .04" (1mm) width of cut and at 31in/min (800mm/min) feed and then it shows just 1 or two faint lines like this at the end of the cut.

[CitizenOfDreams]

Does the period of this pattern correlate with anything? Like, the rotation of the leadscrew?

[coffeetek]

Does the period of this pattern correlate with anything? Like, the rotation of the leadscrew?

Good question, I do not know. It looks like too regularly spaced pattern.

[LeeWay]

Which direction are you cutting?
If it is chatter, you should hear it. Also changing the direction should help. Another thing that may help is to do a roughing and then a finish pass.

[coffeetek]

Which direction are you cutting?

Straight line along Y axis.

[IMT]

Are you climb cutting? Have you checked the lost motion in the Y axis?
If you have excessive lost motion it can cause strange kinds of chatter when climb cutting. See if a traditional cut does the same thing. And measure the lost motion in Y.

[coffeetek]

Little more info, each of those stripes appears to be about 3mm wide (little less than 1/8")...

[coffeetek]

Are you climb cutting? Have you checked the lost motion in the Y axis?
If you have excessive lost motion it can cause strange kinds of chatter when climb cutting. See if a traditional cut does the same thing. And measure the lost motion in Y.

Standard cutting. Have not measured lost motion on Y axis. Will do that today.

[LeeWay]

Right, I was referring to the direction of the cutter as clockwise or CCW around the part.

[coffeetek]

Right, I was referring to the direction of the cutter as clockwise or CCW around the part.

Ah, its clockwise.

[LeeWay]

You should try going the opposite direction.

[Bdrangdo]

What is the pitch of the "Y" screw, it would seem you may have a problem with the screw, ie it may be bent or binding giving a slightly uneven feed. Dave

[IMT]

Standard cutting. Have not measured lost motion on Y axis. Will do that today.

Ah, its clockwise.

If the tool is moving around the outside of the part in a clockwise direction (viewed from the top) then you are climb cutting.

[Jim Dawson]

I wouldn't know how to generate that pattern if I wanted it. How the nice sharp edges on the stripes are generated with an end mill is beyond me.

Having said that, I would be taking a look at the X axis backlash. Maybe try running the cut again and lash up an indicator on the X axis to see how much it is moving. The other possibility that comes to mind is the quill or head is moving in the X axis plane.

[LeeWay]

Normal chatter that I have seen on my small mill looks more of an angle and not a perfect pattern. I usually see evidence of tool flex when that has happened in the past. The pattern looked more like the pattern you miight see on a poor plasma cut.

[coffeetek]

If the tool is moving around the outside of the part in a clockwise direction (viewed from the top) then you are climb cutting.

Yes, my mistake, its climb cut.

I have just tried both climb and conventional cut, it results in same patter on side wall.

I have checked X axis backlash and adjusted gib. Its at 0.01mm. Y-axis backlash is at 0.01mm as well. Z-axis backlash is at 0.018mm. I think these are all within expected values.