Polishing a resin piece to a glossy finish

You just removed your latest resin creation from the mold. It does not look exactly how you expected it. Wanted a shiny glass cylinder. Got a beat up dull plastic puck. Here's how to fix it.

Tools needed:

• Fine metal file (for correcting shape);
• Sandpaper, from coarse to fine: 100 grit, 240 grit, 600 grit (and 1000 if you can), preferrably waterproof. Home Depot has up to 600 grit and is cheap. Auto stores should have 1000;

• Power drill (or buffer tool);




• Buffing kit: 4" cotton buffing wheel and "White Rouge" compound. Home Depot has a "Ryobi 8-piece Mini Buffing Kit" for $10 (part# A01AG08) with everything you need for a standard power drill - comes with two "White Rouge" sticks as seen on the right and the buffing wheel attached to the drill above.
  

First, wait until the resin is fully cured (a week is good).

Know that filing or polishing resin produces a fine dust which is best not inhaled. Do your own research and protect yourself according to your tolerance, but my guess is whatever you wore while casting should work. I'd either use a particulate mask (but still have a mess to clean up afterwards) or work near a sink and wet everything so there's no airborne dust (that's the reason for the waterproof sandpaper). The advantage of wet sanding is also a finer finish and easier removal of accumulated debris while sanding. Do not wet buffing wheel!

File away unneeded material and correct the shape of the object. Careful not to chip sharp corners. Flat surfaces are best handled by laying the coarse (100-grit) sandpaper on the table and running the piece over it in circular motions while applying equal pressure on the object. Don't get carried away and don't use too much pressure, sandpaper eats resin fast. Most of the shaping should be done with the coarsest grit.

Next, use 240-grit sandpaper to finalize the shape, applying less pressure. You can do some fine edge beveling too. Then move to progressively finer sandpaper to prepare it for buffing. All the surfaces that you want glossy must be done with the finest grit (600 or 1000) or you'll have hard-to-remove deep scratches afterwards.

Here's how the dry item looks after the sanding with the different papers. When wet it looks a lot more translucent, it gets duller when dry. The 600-grit results in a nice "frosted" finish very soft to the touch, good if you don't need to see through it, otherwise still not so great.

Now that the piece is in its final shape and has been dried, we need to make the glossy surfaces. Install the buffing wheel on the drill according to instructions that came with the kit. The buffing compound is a very fine abrasive paste which, when attached to the buffing wheel fibers hitting the object many times at high speed, flattens the microscopic peaks left over from sanding. It does not have a lot of grinding power though, which is why we had to use the fine sandpaper first. I used the "White Rouge" compound which is recommended for plastics.

Find the best position you can hold the drill still with one hand for long periods with your face not in the way of the stream of abraded particles, nor in the plane of rotation of the wheel (fibers or other things may detach at any moment and in any direction). A pair of goggles could complete the outfit. You might also need a pair of ear plugs if your drill is as loud as mine, you'll need to use it for longer than usual and the shrieking noise might make your ears ring for a while afterwards.

While the buffing wheel is at speed, load it with just a little bit of the compound - touch the edge of the wheel with the White Rouge stick just a second or two. You'll know you put too much if you see a white waxy "scum" accumulate on the object as you push the wheel onto it. Hold the drill still while moving the object around, touching the edge of the spinning wheel. You should see the surface starting to get a mirror finish right away. The wheel is not effective without the compound so you need to add more as you work. Always add a little bit, and only to the edge of the wheel, not the object.

Caution: always hold the object or the stick leaned towards the direction the wheel is spinning to avoid having it (or worse, the drill) knocked out of your hand and launched across the room or into your face.

Don't press too hard or the resin will heat up and melt. If you feel the object getting warm, let off the pressure. The important factor is the linear speed of the wheel edge, so you can also use a smaller wheel if your drill is too fast.

That's it!