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3D printing has become a huge hit for hobbyists and professionals alike. I primarily use my printer in making various props and trinkets. One of the biggest things you have to deal with when making a piece you want to look realistic is getting rid of those print lines.

This Instructable will cover some basic finishing techniques that will help you prepare your 3D print to be painted or to apply some other medium to it.

Step 1: Sanding by Hand

Pros:

  • The most affordable method of getting rid of the print lines.
  • Becomes smooth to the touch.
  • Gives a glossy effect

Cons:

  • Can cause sharp edges to be rounded off
  • Not great for complex and delicate parts

Tools Needed

Optional

This is the most straightforward method. You're going to treat the print like a piece of wood and just sand it smooth. Depending on how thick and deep the print lines are you may have to start with a very coarse grit. Vice versa, if you have shallow and tight print lines you may be able to start even with a medium grit.

So, have at it. Start to sand in a circular motion around the object. Be careful not to apply too much pressure as you might snap your piece apart. Typically what I do at this point is put on a movie and just sand while I watch. You can expect to spend at least 15 minutes per 2 inches of the surface with each sheet of grit. Sanding this print down to 2000 grit to get the shiny surface took about 2 hours.

You should start seeing a major difference in the feel of the item by reaching the fine grit. From here you can either stop if you want a bit of texture to the item OR you can continue going up in grit until you get to wet sanding around 2000. This will make the print shiny and smooth to the touch.

The major downside of this method is that it will cause sharp edges to be rounded if you are not very careful. Give the pressure applied this is also not great for fragile pieces with delicate parts.

You can see in the picture too that the honeycomb pattern can be seen. To avoid most of this you'd need to print in a high density (between 75-100% fill) or ensure that you increase the size of your outer shell by at least one nozzle increment (for example, if you have a .4 mm nozzle and the standard shell is 1.2mm I'd recommend going up to 2mm (add two increments of .4 to match your nozzle size). This will give you some more material to work with before you wear through the outer layer.

What this method is best used for is rounded prints like skulls, orbs, or other prints that don't have sharp edges.

Step 2: Using Brush on Resin

Pros:

  • Quickest method to remove print lines
  • Gives a really nice surface to apply mediums too
  • Reliably removes print lines completely where it is put

Cons:

  • Most expensive method
  • Resins can be toxic and if not handled right might cause harm to the user
  • You will have to paint or otherwise color over the original material

Tools Needed

  • Paint brushes (various sizes depending on complexity of print)
  • PAPER cups (plastic cups may have a poor reaction to the resin and melt)
  • XTC-3D resin (you can use other resins but ensure you talk to the store owner first to ensure it won't react badly to the material you are printing)
  • Gloves
  • If working in a confined space also get a respirator

Optional

This is, without comparison, the fastest way to get rid of the print lines and move on to the medium application. Read the instructions on the label for the resin. Typically it is a 2 to 1 ratio and you can eyeball it by using two different paper cups and then mixing the two in one of the cups. Once this is done you are on a ticking clock. XTC-3D dries fairly quickly. So, start painting it on the print.

The way to get the best results is by doing several, thin layers in order to avoid streaks or imperfections. So only mix small amounts of resin at a time unless you are doing a large print.

After this dries you can clean it up a bit with some fine or extra fine sandpaper. Then you can apply your medium. I recommend adding a primer first, but XTC-3D claims you don't need to. For this print I applied primer and then used Rust-Oleum's hammered finished spray paint (Gold Rush). I've also used waxes and airbrush with this method with great success.

Another option is to add pigments or other resin friendly paints to the mixture before applying it to the print. This can allow really interesting effects with specialty pigments.

Step 3: Sanding and Priming

Pros:

  • Good medium between sanding and resin both quality and cost wise
  • Gives a similar effect to XTC-3D method
  • Takes less time than the sanding method

Cons:

  • Takes more time than the resin method
  • requires multiple iterations of the method

Tool Needed

  • Sandpaper - Coarse, Medium, and Fine grits
  • Paint primer that bonds to plastic (white is the easiest to see)

This is the in-between point. While it will cut down on time compared to straight sanding and cost less than resin it does take more time to complete and can take several passes in order to get it smooth.

First, sand down the piece with your coarse, medium, and fine grits. Once it starts feeling smooth put a layer of primer on it (go thin with the first two layers to get an even surface). Now, you should see any lines you might have missed.

Using the fine sand paper really scrub down on these parts, almost until you can see through the primer you had on it. After that, spray it again. Repeat this process till you are happy with the surface.

This print was also treated with Rustoleum hammered spray paint (Gold Rush).

Step 4: More Complex Methods

I will be releasing an Instructable soon on more complex finishing methods, so keep an eye out for it!

Some methods I'll discuss are rock tumblers for small prints, acetone for ABS prints, heat gun use, and a few others.

Thank you for taking the time to read my article! If you are interested in seeing more of my work you can see it at Iron Wolf Enterprises

<p>I was wondering about the feasibility of putting a print inside of, say, a paint can, with some fine grit sand and rotating it. I see here you mentioned a rock tumbler, I wonder if we're both thinking along the same lines?</p>
<p>Lots of good tips! Thanks for sharing :)</p>

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