[motoeng]

I just received some sample parts from my machinist and would like some input before I speak with them regarding this issue.

Some of the sample parts have a hazy, almost matte surface finish on a particular horizontal surface. I'm assuming this surface is machined with an end mill as opposed to a face mill simply due to the small size of the part and the adjacent vertical surface that lends itself to machining via end mill.

I would like to know possible causes for this to educate myself. Any responses are appreciated.

[awerby]

Did they do any post-machining finishing on those matte parts? Like vibro-tumbling, bulk deburring, anything like that? Ceramic media often leave a finish like that.

[motoeng]

Did they do any post-machining finishing on those matte parts? Like vibro-tumbling, bulk deburring, anything like that? Ceramic media often leave a finish like that.

No post finishing other than some manual deburring on some sharp edges.

[the_gentlegiant]

They simply changed end mills mid stream for whatever reason. One the very end of the end mill is sharp, the other not so. Same tool path. Same everything. You can even see a very slight burr on the dull tool part. I doubt it's going to make any difference at all how the part works. If you did not spec any surface finish tolerances or supply samples, you have nothing to stand on. It's not poor machining per say. I'm sure the person had an, oh sh*t, I don't like what that end mill is doing any more. Time to change it out. Situations like that are not uncommon.

On second thought it might even be from a different stick of raw stock. Every once in awhile aluminum will change a little on you from one stick to the next. Mostly though I think it's a dull-ish cutting end.

I like the hex work. That's pretty sweet.

[dazp1976]

I find flood coolant can make parts look dull too.

[motoeng]

Thx for the replies. It's possible they switched tooling between samples. I'm curious to know the type of tooling and feeds/speeds used. I will ask.

[machinehop5]

...maybe add a surface finish tolerance to your drawing for that area, than the machinist would know to slowdown feed rates. There are devices called a Profilometer if, you really want to check a surface.
https://en.wikipedia.org/wiki/Profilometer

DJ

[motoeng]

...maybe add a surface finish tolerance to your drawing for that area, than the machinist would know to slowdown feed rates. There are devices called a Profilometer if, you really want to check a surface.
https://en.wikipedia.org/wiki/Profilometer

DJ

There is a 0.8 RA finish on that surface (micrometer). I've not been able to justify the high cost of a profilometer. I just go by look and feel.

[the_gentlegiant]

Just remember, adding tolerances of any type, especially critical or tight ones and perhaps especially surface finish, come with the associated dollar signs attached to them.

In general, I wouldn't call the end of an end mill the best surface finish tool around. Wiper flats can help, but still.