Problem- Blotchy finish on AL 6061-T6 "toy" turnings

[Gitman]

Hello all,

My first post. Great site and resource for information, I'm a daily reader. I have a problem on a part I'm making on my cnc lathe. The turned parts are "adult toys" <insert joke here> made from domestic Kaisar or Alcoa Aluminum 6061-T6 in diameters ranging from 1 to 1-1/2 inches. I'm using a Sandvik VCGX high rake insert made for aluminum at 1800 rpm and .005in/rev as a finishing pass on the part. I'm only spinning at 1800 because I'm making these parts in a 3 jaw 10 inch chuck on my Hwacheon lathe. I'll be switching to a collet chuck once I can afford it. I use Blaser 2000 coolant.

My problem is this. I get a good surface with this tool and feed, but the parts have small white hazy spots that show up after machining and anodizing which gets rejected from a very picky customer. I've gone thru everything I can think of. This includes monitoring coolant percentages and ph level. We replaced our coolant and used a bacteria killer in the tank. We then replaced the coolant and added a metal deactivator. Still getting spots.

At this point, I believe the problem is minor impurities in the material I'm getting. To fix the problem the parts either have to be hit with scotch-brite and or bead blasted to remove or hide the spotting...at added time and expense. I'm making 1000 of these parts a week. The spotting is becoming a big problem.

Any insights would be appreciated. Wondering if anyone else has experienced this? I need a better camera to post a close up picture. I'll try to post a picture later this week.

[HuFlungDung]

I believe I have seen the phenomena that you are referring to. It is actually the crystalline state of the material itself. I noticed this when turning parts from 1.5" diameter extruded 6061-T6. I do not know if all sizes of this material exhibit the same condition, but only that one job seemed to really have an exaggerated effect this way. I had to buff the surface with scotch-brite to try to blend and hide it.

[laka]

We've experienced this before. Two things that have worked for us are using a little larger stock size (maybe 1/8" in diameter). Or try getting some grey (fine) scotch-brite pads and giving them a little polish afterwards.