SD card holder 3D printed and acetone vapor treated. These are the steps I used.
1) Your print needs to be ABS for this to work with Acetone.
*** Acetone is very toxic and flammable. Follow all safety precautions on the container!!! Only use in a well ventilated area or outdoors. ***
2) Find a container that does not react to Acetone. The Ziploc or Glad brand plastic food containers are good, or most anything stainless steel. Acetone is usually sold in a steel container. The container needs to be larger than your model of course.
3) Use a metal cap or some other kind of small container with a low lip. This will go inside the larger container and hold the pool of Acetone. Do not let the model touch any liquid Acetone.
The Glad container I used has a convenient round section in it’s top. I turn the container upside down and place the model on what would be the top of the container. The model is set so it does not touch the edge of the container and does not touch any wet acetone. Lay a couple torn pieces of paper towel around where it will not touch the model. If you use stiffer paper, you could also use a paint can and put the paper vertically inside along the wall.
Dip one end of the paper into the acetone pool. This wicks the acetone into the air making more vapor than there would be from just the pool.
4) Close the container and wait. Depending on the volume of air and the amount of paper you can get to wick the acetone, will determine how long it takes to smooth the model. I like this container because I can still see pretty well if the lines are smoothing. I don’t have to open the container every time I want to check the progress.
Check check the container after about ten minutes or so. Then check every 20-30 minutes. If you wait too long, your model will definitely melt. If the model has thin walls or is itself made of thin parts, you may need to vapor it for 20-30 minutes, then take it out for a couple hours and repeat.
5) When the model is as smooth as you like, take it out of the vapor bath. Handle the model gently and preferably without touching any visible surface. Depending on how long it’s been in the vapor, the surface may be stick and could pick up your fingerprints just by touching it.
Leave the model in an open are area for several hours. The acetone that was absorbed needs to “off-gas”. It will stop smelling like acetone in a day or two depending on the thickness of the plastic treated.
Another reason I like the upside-down container method, is I can easily spatula my model off the lid without having to reach into a tall vertical container.
You can do any version of this containering. The plastic containers are cheap enough that I cut them up to make bigger containers for taller pieces. I found packing tape will keep the two boxes together. If you do tape containers together, check that the tape still sticks after 20 minutes or so. If it doesn’t then you’re letting Acetone vapor out and into your area. Try a different one until you find one that doesn’t react to the Acetone vapor.