cutter vibration or machine fault?

I'm machining some cool 3d parts and some sections have odd cutter marks.
It's as if the ball nose end mill is cutting at slightly different depths.
You can see them but barely feel them with your fingers.
I'm guessing less than half a thou.
Interesting that their location is at the point where there is a double step.
Plain round sections are flawless.

I'm using a 1/4" 2 flute ball end mill sticking out 1.35" from the tool holder.
6000rpm (max), 0.005" cut depth, 0.005" stepover at 24ipm.
Wondering if its cutter vibration or is my Mini Mill worn out?

Timothy

Try using G09 Exact Stop

I don't think a G09 will help.
I added a small 5 thou radius in all the tight corners so the cutter wouldn't have to stop and it still makes those lines.
I reduced rpm and cut the feed rate in half.
Still no difference.
Tomorrow I swap out cutters and tool holders.

Timothy

I'll have this problem at times. I believe it's a problem between climb and conventional cutting since the path is a zigzag.
I've minimized the problem by making the tool 2 flute and new. And if it's still an issue I'll make the path zig only. This adds a ton of time but when I have to, well, I have to and it works.

does your mill have the high speed machining option , those machines can be pretty jerky without it . Also have you tried g187 ?
There is a setting that adds a bit of rounding to smooth things out but it's been a while so I can't remember what setting it is

We have high speed machining. I’ve tried G187 P1 through P3 (its been a while so memory hazy). I ended up keeping it on the medium setting I think. Havent looked at it since the first experiments. I can look Monday. I was having the same problem on our new at the time VM-3 as our 5 year old VF-2ss. So I concluded it was just the nature of the beast but I sure hope there’s a better answer than mine.

No high speed machining.
A G187 seems like it's just a G09 but for the whole program.
Setting 85 is set to 0.005"
I switched out the cutter for a new super high quality one and even put it in a brand new tool holder.
Still the same.
Then I changed the tool path to a climb mill zig only.
Still there.
What's really frustrating is that on other parts of this piece the contours are absolutely perfect.
Since I bought this Mini Mill used, I'm wondering if there are some parameters that have been altered.
Is there a quick way to reset to all the default settings?

Timothy

Could you rotate your part 90 degrees, repost the program, and try cutting it again? If you have an axis issue, that might bring some things to light.

To me, 1.35" hanging out on a ¼" cutter seems like a good bit, though you've made big changes in revs and feed with no apparent change, it sounds like? ER holder?

PM

I rotated the part and ran a few different versions.
The marks moved with the part to the new location.
First ball end mill was in a side lock tool holder.
Second one is in an ER20 collet.

I'm leaning towards a CAM fault.
The G19 circular path in made up of five or six segments in the problem area.
The larger areas with no deviances from the circle are one or two circle segments and they are absolutely perfect.

Timothy

Timothy,

What are you using for CAM? If it's Fusion 360, and you don't have any secrecy-related issues... could you upload the F3D file or email it so I could take a look at it?

PM

flawed finishes aren't uncommon with haas but if rotating it produced the same results then it's going to be in the programming . a tighter tolerance in the cam software might help with blending oddball spots together better

I'm using BobCad/CAM Ver30 pro.
And this job has a disclose agreement attached to it.
Although I might be able to clip out a section...
Which format is best for you?

Timothy

Hi Timothy,

I don't know if you ever got the answer you needed, but I've used Bobcad for 14 years to build molds from V21 through V30. The geometry problem you are seeing is purely bobcad's fault.

1st: Make sure the model's surface normals are correct.
- If any are inside out, fix them re-select the geometry and recalculate the tool path.

2nd: Play with the accuracy settings in Bobcad.
- Arc fit, corner rounding, smoothing, and general tolerances all play a part in the delicate ballet of calculating the best tool path.
- Counter-intuitively, Tightening tolerances may not always be the right answer. Bobcad might detect micro deviations in a model's surface that aren't rendered on screen and therefore jitter bugs the tool across the surface. Loosening tolerances may let Bobcad ignore these imperfections and smooth the tool path.
- Sometimes if you blank the model and zoom in on the toolpath from the correct angle you can actually see on screen the gouging moves.

Machine settings are important too, but I'm sure Bobcad bears the most blame here.

https://youtu.be/vt7rVVRiiKk

https://youtu.be/lwujoXvgGzA

Good Luck, I hope I was able to help.

Thanks for the reply bishb25,

I did change a few setting within BobCAD but I didn't see any differences when running the part.
I have another batch coming up in a few weeks so I'll try G187 and see it that fixes it.
At the same time I'll look real close at the tool paths to see if anything is out of place there too.

Timothy

Quote:

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Originally Posted by 2ferrous

I'm machining some cool 3d parts and some sections have odd cutter marks.
It's as if the ball nose end mill is cutting at slightly different depths.
You can see them but barely feel them with your fingers.
I'm guessing less than half a thou.
Interesting that their location is at the point where there is a double step.
Plain round sections are flawless.

I'm using a 1/4" 2 flute ball end mill sticking out 1.35" from the tool holder.
6000rpm (max), 0.005" cut depth, 0.005" stepover at 24ipm.
Wondering if its cutter vibration or is my Mini Mill worn out?

Timothy

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The cutter is having a merry old dance