You might want to look into vibratory deburring/polishing. There are several threads about it here and a nice summary here: http://www.cnccookbook.com/CCVibeDeburr.htm
I am trying to learn more about bead-blasting, polishing, and/or chemicall etching 6061 aluminum, and what I can expect from each in terms of the work involved and the final result.
Example -- I have several pieces of 0.25" thick 6061 that were plasma cut. The largest is smaller than a square foot in total area and measures less than 12" on it's longest side. They were cut from plate and have scratches and mars that will be visible after anodizing if nothing is done to prep the surface. I will be anodizing several at a time in my small line.
My #1 priority is minimizing the work involved in hiding the scratches. Having a matte vs gloss finish is not critical for my application, I just need a workflow that will produce a uniform finish AND that hides preexisting scratches.
I have read that chemical etching using NaOH solution provides a matte finish, but I don't know if it goes deep enough to etch away the scratches.
I've already paid for some bead-blasting services in the past and it did a great job of meeting both goals, BUT I understand it can be more difficult to make it uniform and is also difficult to get a deep black anodize with a bead-blasted part.
I have never polished aluminum but I'm not opposed to it if a uniform finish can be achieved more quickly than either bead blasting or chemical etching. My assumption was that polishing would be the most time consuming so I've focused on the other two, but correct me if I'm wrong.
Again, matte vs gloss isn't important, but the time required to hide the surface imperfections is.
Thanks for your help.
Last edited by imhotep; 12-07-2009 at 10:40 AM.
After some quick searching I don't know if this will be a good option for me. My largest piece is about 12.6" on the longest side and it takes a fairly large and expensive tumbler to hold something that long.
Bead blasting is going to be your easiest/fastest. Depending on how deep the scratches are you may want to do some light sanding first, try using around a 300grit. When you blast just go over and back, if you spend too much time in one area you will get a blotchy ano finish. As far as blasted parts not looking as dark, that depends on how much blasting you do to the part, the lighter he blasing you can get away with and still cover you scratches the darker your part will look.
I have also gotten away with just sanding in the past. 300grit, 600grit, 800grit wet sanding gives almost a semi-gloss finish. Easy finish, but if you have a blasting cabinet, I would go that route.
Thanks, sanding was going to be my next question actually. I do not own a blasting cabinet yet, but I do own a good drill press and some hand-drills, both corded and cordless. I also have a random-orbit sander, but I'm not sure what kind of sand paper is best to use wet with metal, or if they make it in pads for a random orbit sander? What power tool did you use to sand with the increasing grits, or did you sand by hand?
You should be able to pick up wet/dry paper at any hardware store. I use a rubber sanding block and do it by hand. You will have more control over the finish by hand. As you already mentioned anodizing does not cover markings. It would serve much purpose to replace scratches with sanding marks.
Good point, but I would favor an evenly etched surface (i.e. one that looks uniform and intentional) over descrete scratches that obviously are not intentional.
I have read some articles that are in favor of using a random orbit sander for applying a uniform surface on aluminum because the random sanding doesn't leave a swirling pattern. I already knew this worked well with wood even across grain because it's my sander of choice for woodworking, but it makes sense it would also provide a uniform quasi-brushed appearance to metal as well. Since I"m already equipped for this I will start experimenting.
Iím curious on how the finish turned out using your sander.