[kaibecker]

Hi All,
I'm a Newbie to machining so please pardon my ignorance.
I hope to get some advice from all you experts out there on how to avoid rough surfaces on vertical 90 degree walls.
This maybe a rookie mistake, but we are using a Z-Finish code with a 1/8" ball endmill, hanging out 2.5"
Thanks in advance.
KB

[GEECODEMILLI]

What version of bobcad are u running? might be an issue with ur steps/depth of cut
If you have your hands on the Advanced Rough future you might wanta give that a shot.
But in general a Z level is a roughing tool so you shouldn't expect a super smooth surface.
Ive came pretty close with the right stepover amount for my tool.

[Billetgrip]

Just use 2 Axis contour and mill it with the biggest bullnose endmill that will fit if it needs a radius on the bottom.

[Fletch_CNC]

That's really far to be hanging that little endmill out. In general, you want to keep tools as short as possible. Also, is your tool relieved back? If the shank rubs, you'll get a crummy surface, too.
I agree with the above advice: use a bigger tool, and make a regular profile-type cut if you want smooth walls. If you do have to cut that sort of surface with a ball nose, my experience has been that making cuts one-way going down the surface (waterfall motion) will give you the best surface. That's because ball noses cut best towards the tip.

[triumph406]

. That's because ball noses cut best towards the tip.

Ball nose cutters cut the worst at the tip, and the best on the side. The only ball nose cutters I've used that gave an acceptable finish when cutting with the tip are Dapra's with the single insert. We contour parts with a 3/4 Dapra cutter with .0005 scallop height to finish. The finish is noticeably better when it's not cutting on the tip.

[Fletch_CNC]

Ball nose cutters cut the worst at the tip, and the best on the side. The only ball nose cutters I've used that gave an acceptable finish when cutting with the tip are Dapra's with the single insert. We contour parts with a 3/4 Dapra cutter with .0005 scallop height to finish. The finish is noticeably better when it's not cutting on the tip.

I said towards the tip, not on. And you do have to make sure to account for the actual cut width when finishing like that. I've cut a fair amount of A2 and 4140PH for prog dies, so I do have some idea what I am talking about. Not that I know everything, of course! lol Like an old timer told me once, "There are lots of ways to do things in machining. Some people do things my way, and other people do it wrong!" lol

You're right though, cutting in more of a profile motion can do the job really nice, too. The die in my avatar, I cut the center dome punch (it was about 18" across, A2) with a surface profile-- one long cut. Lead in at the top, lead out at the bottom, and slowly spiral down the surface. That came out pretty slick. Keeping the tool in contact with the part as much as possible is a good tip, too.