Jul 20, 2018

Blender: How to Merge Objects – Simply Explained

Sometimes in Blender, an object you're modeling is too complicated to model in a single object, so it's easier to make two (or more) objects and then merge them together later. However, it's only easier if you know how! Here's how to merge together objects in three different ways.

Blender - How to Merge Objects "Joining" Objects

The process of joining two cubes so that they behave as one object Source: Blu Siber / All3DP

This is the easiest process we’ll look at. Though one of the most commonly used tools, it doesn’t work the way a lot of people expect.

Joining objects does not geometrically connect them together. It simply “marks” them as one object. This means they move, rotate, scale, and animate like one object, but they are not attached. So if you 3D-print an object “joined” in Blender, it wouldn’t print as one object. Rather, the result would be multiple objects.

That said, joining is still incredibly useful for working with complex scenery or characters, or when working with a print that must be assembled. You can join the pieces in their assembled state, and then have them printed individually.

Before joining objects, there are a couple of things to understand:

  • One object be the “parent” of all of the others that are getting joined. You must choose the one you think is the most prominent, and let that one be the parent.
  • You must remember that even if the objects are touching when you join them, they do not connect together. They are still detached from each other, and they are only intersecting through each other. Joining simply makes them act as one object. For this reason, it’s not recommended to print when there are intersecting or contradicting objects in a model.

Here’s how to join two or more objects:

  1. Right-click to select the first object, one which you do not want to be the parent. Once it is selected, hold down shift and right-click the other objects you want to join. The last object you select is the parent.
  2. Once everything you want joined is selected, you can either left-click the “Join” button in the toolbox (as shown in the image), or you can simply press CTRL + J on your keyboard. Now, both objects look, move, and act as one.
  3. If you cannot see the toolbox in the 3D editor, hover your mouse over the editor, and press T on your keyboard. Alternatively, you can left-click the tiny “+” tab near the top left corner of the 3D editor. The toolbox will appear, and can be dragged further if desired. To hide the toolbox, you can press T while it’s visible, or drag the right edge of the toolbox all the way to the left until it disappears.

This is a very handy tool to have, but what if we really need to connect two objects together? Not to worry! Though it requires more steps, it’s still rather simple.

Blender - How to Merge Objects "Adding" Objects Together

The process of adding "cube_top" to "cube_bottom" Source: Blu Siber / All3DP

If you need to attach two objects together, joining them obviously won’t work. However, using modifiers, we can achieve just that with minimal effort! Again, you’re going to need to choose a prominent object. Also, this method only works with two objects, so if you have more than two objects to attach, then simply repeat the process for each extra object.

Here’s how to add two objects together:

  1. Select your prominent object by right-clicking. In our example, we’re using the lower cube as our prominent object. Make sure it’s the only object that’s selected. Then, locate the properties editor. In the default view (and in our example), it’s located on the right side of the screen under the outliner. Select the modifiers tab, the one with the wrench on it.
  2. Click the “Add Modifier” button to show the list of available modifiers. You can select a modifier by left-clicking, scrolling and middle-clicking, or using your keyboard arrows and pressing enter. In this case, select the “Boolean” modifier. Once added, the name of the modifier might be highlighted red. Don’t worry, this will disappear soon.
  3. To continue, you must know the name of the other object you’re trying to attach. In our case, the object we’re trying to attach to the selected cube is named “cube_top”. Looking at the right side of the modifier, you’ll see a blank button under the section marked “Object“. Click in the empty area, and a list of objects will appear. Select the object you are trying to attach.
  4. Something did indeed happen, but not in the way we wanted. To fix this, locate the “Operation” section in the modifier, and click the dropdown button just below it. From the list, choose “Union“. Both objects should now be attached!

Once you’re ready, scroll down to the section in this article titled “Applying Modifiers” to finish the process, reducing it down to one object.

Blender - How to Merge Objects Bonus: "Subtracting" Objects

The process of subtracting "cube_top" from "cube_bottom" Source: Blu Siber / All3DP

Note: This is not a method of connecting or joining two objects together. Rather, it’s a useful method of engraving or cutting an object to get rid of another.

Sometimes, you’ll find a need to cut out a piece of an object using another. This is useful in cases where you want to engrave text or a shape into an object. This can easily be done using the boolean modifier.

Here’s how to subtract one object from another:

  1. Follow the first two steps of the previous method. Keep in mind that the object you first select should be the object that you are cutting. (This part is not shown in the image.)
  2. Once you have your modifier added, locate the button directly under the “Operation” text. Click it, and from the list select “Difference“.
  3. Next, click the empty box under the “Object” text, on the right side of the modifier. From the new list that appears, select the object that you want to cut the selected object with. In our case, we want to cut the bottom cube with the top cube.
  4. (Note that you won’t see the results of the cut, yet.)

Once you’re ready, move on to the next section to finish the process.

Blender - How to Merge Objects Applying Modifiers

Applying a modifier and deleting the second object Source: Blu Siber / All3DP

You may have noticed that your object doesn’t yet look the way you wanted it to.

That’s because we’re not done yet! The image uses the example from the subtraction section, but the same process applies to the addition section as well.

Here’s how to apply a modifer:

  1. If you’re here, then you already have your modifiers set to what you want. That means we only have two things left to do. The first is to click the “Apply” button on the modifier to save the changes to the selected object.
  2. Now, we need to delete the other object involved in the modifier. To do this, we must first select it. If the second object is still visible, right-click on it to select it. If you can’t select the second object without selecting the first as well, then use the outliner. The outliner is usually at the top-right corner of the screen in the default view (and in our example). Left-click on the name of the second object, and then move your cursor into the 3D editor.
  3. With the second object selected, press Delete. You can then press Enter in the confirmation dialog, or left-click the highlighted button.

And there you have it! Whether you chose to use a modifier or the join command, you now know how to merge objects together in three different ways, thus enabling you do do more with your models!

License: The text of "Blender: How to Merge Objects – Simply Explained" by All3DP is licensed under a Creative Commons Attribution 4.0 International License.

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