You might have read the instructable on how to polish big resin pieces from the Objet 3D Printers. But what if you want to polish a small but complex part? When a sander is too big and powerful for your delicate little part? In this instructable I'll demonstrate how you can polish a small 3d printed part using jewelry polishing techniques.
This method works for: investment-casted metal pieces, 3d-printed metal pieces (steel, bronze, precious metal, etc.), and 3d-printed resin pieces.
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Step 1: Set-up Work Station
Since our part is small, we need good control on our hands to polish it well. A flex shaft is ideal, but if you don't have one, you can easily modify a dremel into a flex shaft using a simple attachment. When you purchase this attachment make sure to check if it works with your dremel model.
Attach the flex shaft attachment to a dremel, and find a spot to hang your dremel upright. (You don't want to put it on the table since the vibrations will be super annoying). Make sure the cord of the attachment forms a light and easy curve from the head of the dremel to your working table. A sharp curve will damage the tool.
Step 2: Polishing Wheels
Jewelry polishing wheels (here I used AdvantEdge silicone polisher) come in different grits, sizes and shapes. These different shapes (disk, flat-edged disk, teardrop) are very efficient in working on complex geometries.
The white wheels are the most coarse, relatively equal to 400 grit sand paper; the black wheels are medium coarse, relatively equal to 800 grit sand paper; the blue wheels are fine wheels, and can bring your part to at least 1200. There're finer wheels than blue too, in pink, but usually for general purpose blue is fine enough.
Use a screw mandrel to secure a wheel to your dremel. If the mandrel is too thin for your dremel opening, an easy hack is to tape it to make it thicker.
You can purchase all of the polishing wheels as well as the screw mandrel from Rio Grande.
Step 3: White (coarse) Wheels
Clean and dry your 3d printed part thoroughly. Here I printed a model of a chicken pox virus using vero clear on an Objet 3D Printer. You can see all the texture from the 3d printing process very clearly.
Start with white wheels. They are very efficient in removing the 3d printed texture and other small scratches. Recommended speed is 1,000–5,000rpm with very light pressure. If you press too hard, you start to create new dents on the surface.
After using white wheels, the whole surface will look blurry. Clean your part and examine if there're still scratches left. The white wheels should be able to get rid of all major scratches on the surface.
Polishing wheel dust is annoying so make sure you wear proper protection gears (respirator / mask, safety glasses, apron, etc.) while you're polishing.
Step 4: Black (medium) & Blue (fine) Wheels
Continue with black wheels and blue wheels. Your part should become more and more clear when you move up grit.
Step 5: Sand Paper
An alternative sanding technique is to use sand paper. Similar to polishing wheels, jewelry polishing sand paper comes in many different grits. The green sand paper (400 grit) and grey sand paper (600 grit, no picture here sorry) are frequently used to remove small scratches. All these sand paper is for dry sanding. Note that although the green sand paper might seem pretty coarse (400 grit for example), they are actually very fine and soft sand paper and are not really comparable to the white polishing wheels. They're better for later stage polishing when you already have a pretty smooth surface.
Sanding with sand paper by hand is very labor intense. But here's a little trick. Stick a small piece of sand paper in a slotted mandrel and now you can use your flex shaft / dremel to drive the sand paper.
Some jewelry polishing sand paper can be super fine (6000 grit) which is a little bit unnecessary for general purpose. But go for it if you're OCD.
Step 6: Polishing Compound
The last step in polishing is to use some polishing compound. Use a brush wheel with tripoli (a pre-polishing compound) first. Then wash your past thoroughly before you move on to rouge. This is to prevent the rouge wheel from contaminating with left-over tripoli. If you have a ultra sonic cleaner, soak your part in warm soap water for 5 minutes to get rid of all the tripoli.
Then use a cotton or felt fluffy buffering wheel with rouge. Your part should start to have a beautiful shine at this point. If the rouge is somehow stuck on the surface, it means either you're not pressing the wheel hard enough, or your surface is not smooth enough for the final step and you should go back to previous steps.
Step 7: Final Result
The finished result should be smooth and shiny.
One last note: there's no fixed method of polishing. Wet sanding should also work for this test piece. Just try out different combinations and see what works best for you. Happy sanding!!