[jpchapboy]

As an endmill enters a cut (particularly as it moves around the final pass on the outer profile of a part it flexes a little away from the part. then as the tool completes the cut all the way around and moves away from the part it tends to leave a little mark that is visible and can be felt. I think it might be called a registration mark.

On a recent batch of outsourced parts I noticed this blemish was fairly distinct, enough to feel the bump with a finger nail. The problem is the face the mark is on is the worst location it could be because that face is a heat transfer face in the assembly, meaning I want that face to fit tightly against its mating surface. Any imperfection on that face might reduce heat transfer. And just as easily the tool could have started on a different face.

I am already reving my drawing so I want to put something in to tell the MFGr to not leave those marks on that face. What is the best way to do this?

I am leaning toward a 125 micro finish. I don't want them to grind that surface or get too caught up in perfection. I just don't want any machine marks there.

[Wrat]

First off, you can add about any note on the drawing you like. So that's up to you.

Also, this can be averted by using circular path entrance and exit. Or, as easily, keep cutting until you get to an outside corner. Altogether too often, programmers just "take the path of least resistance" and do whatever the computer comes up with. This is one of those results that, like you say, might not matter, but sometimes it does. Depends on how much of the process you have control of or can recommend it might be cured without a drawing rev and simply a tape edit.

I have placed shadow profiles of cutters on hogout parts to show how to cut the area in question. This is completely allowable (at least in aerospace).

In ANSI Y14 you can declare a Coplanar feature callout. Or, you can declare the surface a Datum and declare the feature within the limits of the datum that you like. This way, you needn't require a mirror finish to the machining, but can hold them to a flat (or straight) surface without any bumps.