[Crimson11]

Good morning,

I did my first machine relief using Artcam.

My cnc is homemade so it is not that much rigid and cannot go over 1250mm/min (50ipm)

I first did a 6mm roughing pass then did 2 mm ball nose pass for the finish. The material is poplar.

The settings were, 2 mm diameter, 1000 (40ipm) feed rate, stepover 0.2 mm and stepdown 0.5 mm. and it was 15000 rpm.

As you can see the surface finish is not even close to what it should be with scallops/waves and other problems.


Any ideas what I was doing wrong?

Thanks a lot in advance.

[awerby]

It doesn't look that bad to me. The "waves" are probably due to the lack of rigidity you noted. The scalloping is pretty much what you'd expect from a step-over that's 1/10 of the tool diameter on a finishing pass. If you want that to go away, you'll need much finer step-overs, like 1/33 of the tool diameter. And even then, you'll notice it in steep areas.

[Crimson11]

Thanks for the reply. So you are saying I should go for sanding paper instead of wasting time with slower speed etc. ? So cannot be improved?

Here is new try with half 1200mm and the other half 640mm/minute.

[awerby]

That's not what I said, although the time it took to sand out the marks might be less than the extra machining time it would take to eliminate them. What I was suggesting was not a slower feed rate, but a finer step-over. That's the distance (.2mm in this case) each pass of the tool is from the previous one. When you're using a small ball-nose cutter, these have to be fairly close together to eliminate the cusps (the ridges between the scallops) you're noticing. The feed rate isn't going to make any difference with that. It's probably going slower than the commanded feed rate anyway, since it's not going to move forward until each tiny Z axis move is complete, which slows things down a lot on 3D parts.

[Crimson11]

Thank you for the reply. I got it that i need to lower the stepover but it seems that it will take forever to finish the job. Let me do some tests tomorrow.

[awerby]

I usually prefer letting a job take forever on the machine rather than requiring me to take forever sanding it by hand, but it's up to you...

[Crimson11]

Yeap! After I tried to sanding it, I realized that it is not that easy depending on the piece.

I also found out that the Z axis was not perpendicular to the table. I will make a new try tomorrow as soon as I receive the new 6 mm end mils...