Introduction: How to Merge Objects in 3D - Union Vs Merge - the Many Ways | SelfCAD

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In one of my previous Instructables about How to Hollow Out Objects, I placed emphasis on the importance of knowing the unique uses of similar tools as well as their limitations, so that you’d be able to choose the optimal solution to any problem you may encounter during modeling.

In today’s material, I’d like to point out the differences between Stitch & Scoop’s Union tool, and the Merge Objects tool in SelfCAD. As you can tell from their names alone, they share the same function, but the way they work makes a huge difference.


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Step 1: Merge Objects

Let’s start with the Merge Objects tool. You can find it the Utilities drop-down list in the menu.

Step 2: Printing

When you use this option on 2 intersected objects you'll see that the tool did its job correctly, but there is a problem when it comes to the wireframe.

When you'll change the mode of the display to Wireframe, you'll see that the Merge Objects tool kept the inner edges inside the object, and that would pose a problem when you'd send this to printing - the inner edges create an incorrect volume of the model which makes it impossible to print.

Step 3: Magic Fix

Now, we could try to salvage this by using another one of SelfCAD’s tools called Magic Fix, which is located in the Tools drop-down list, however, there is a problem with this option, as it adds a lot of extra edges, vertexes, and polygons to your figure, which can slightly round the edges of your 3D model, and that's not something you'd necessarily want.

There is a situation when using the Merge Objects option would be warranted and I'll get to it, but let's first solve this problem with intersected cubes.

Step 4: The Union

That's when we'll use the Union option, which is located in the Stitch & Scoop tool in the menu.

Step 5: Wireframe

Now, when you look at the textures after using the Union option, you'll see, that the effect is exactly the same as when we used the Merge Objects tool, but there is a change in the wireframe.

As you can see, the Unity tool made quite a mess because of its unique way of creating polygons, so let's first clean this up, so you'll be able to see why this tool is better in this particular situation.

Step 6: Resolution

We can get rid off the unwanted segments by using one of the SelfCAD's tools - the Resolution. Head on to the Modify drop-down list in the menu, and select Resolution. To simplify the wireframe, set the Detail Level to 0 and confirm the changes (you could also do the exact opposite - add complexity to the model - by setting Detail Level to 6, but that's a topic for another Instructable).

As you can see, by using the Union tool we removed all the inner edges that would interfere with 3D printing.

Step 7: The Use for the Merge

As I said earlier, there is a situation when using the Merge tool is warranted, and it’s when you want to merge objects that don't intersect each other. In such situations, the tool itself will not be able to create any inner edges that would interfere with printing, and it won't add any unnecessary segments that we'd have to clean up later.

On the first picture, you can see a simple square positioned at the top of the cube. After using the Merge tool at the two models, they formed a simple, perfect cube, that's ready for printing.

And that’s how you merge models together in different ways in SelfCAD. After this episode, you should know the differences between the Union and Merge tools, and how they can affect your printing. Feel free to share your thoughts on the Instructable in the comment section below.

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