Achieving required surface finish

Hi guys
So I have a client that requires a 8um to 11um surface finish to be produced on a vertical mill. While this is 100% achievable on the centre line of the cutter, due to the nature of a vertical mill as you move away from the centre the actual surface finish decreases in courseness and then the step of the cutter modifys the surface finish again. I have been able to produce something that pretty close using a high feeed cutter with a 50% Step over and when comparing with a scratch gauge it is comparable but visually it has a rail road effect that the client is concerned about.

Despite my best attempts to explain to the engineer looking after the project that it is within the drawing specs and using a vertical mill the above issues are unavoidable he is still not happy with it.

Apart from machining a piece of steel with straight lines using a engraving tool to produce a 8um to 11um surface finish and using it as a forming die to produce the correct finish on the aluminum I'm all out of ideas.

Any thoughts or ideas would be appreciated.

Thanks

Wouldn't lapping be a more reliable way to get the desired finish? Seems to me that the mill is not the right machine because you never know when you'll get an accidental chip scuffing the surface, which is enough to spoil it.

HuFlungDung said:

Wouldn't lapping be a more reliable way to get the desired finish? Seems to me that the mill is not the right machine because you never know when you'll get an accidental chip scuffing the surface, which is enough to spoil it.

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8-11um is actually a very coarse surface finish which i think is the point, typically you will get 1.6-3.2um(or better) with a facemill.

the only thing i can think of is to use a cutter much larger than the surface so only the center of the cutter is over the work peice, of course this may not be practicable depending on the size of the part, you would also need a cutter without wiper flats.

this is something where a shaper or planer would actually be really handy.

End mills and many face mill cutters have a dish originating outermost at the face and falling away from the part going towards. I have made end mills and face mills to have a very small flat (yes with clearance) so that flat covers perhaps on or two feed revolutions for achieving better surface finish. Perhaps you might find a local cutter grinding shop to make a cutter like this.

Your right a shaper would be great unfortunately we don't have one to play with. The area to be machined is roughly 400mm square on about 200 varing parts. So finding something that's efficient is important.

Do you have access to EDM? If it's a flat surface the electrode would be stone simple, and you could play with discharge parameters until you got the finish you desired. It would be pretty random craters too, so there wouldn't be a concern of "rail road" as your customer has expressed.

If you have an angle milling head for your mill, you could make parallel passes with the side of a chamfer style mill. I'm thinking set the angle head at 45 degrees and use a 45 degree chamfer mill. You'd have to doctor up an insert to make it into a serrated rougher.

HuFlungDung said:

If you have an angle milling head for your mill, you could make parallel passes with the side of a chamfer style mill. I'm thinking set the angle head at 45 degrees and use a 45 degree chamfer mill. You'd have to doctor up an insert to make it into a serrated rougher.

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No the machine it is being done on is a straight 3 axis.

At the moment i am leaning towards a knurling tool modified to suit, passed across the surface with spindle lock on i hope it would form the finish in a uniform way.