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Joining/seperating 3D solids.


MathU41

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Okay, maybe my search-fu is just sailing me here, but I haven't been able to find anything useful yet. :glare:

 

I made an object, complicated enough to be a pain to remake from scratch, to be 3D printed. It needed to be a single solid item, which I did but can't remember exactly how (union?), but now it needs a smaller-scale, relatively thicker version, with other little adjustments including the hollow sections inside.

 

And that's where my problem is. I can't delete pieces of it, because trying to select anything selects the whole thing. I try 'explode' and end up with a bunch of faces, which from there won't recombine into a solid.

 

So, I'm sure there's an easy way, or I'm just throwing a wrench in the easy way's works, but I've just been stumbling over trying to find the way to un-combine pieces, then re-combine them.

 

Some help? :oops:

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Actually, it's not always easy to "un-Union" a Solid. SLICE (SLICE > 3Point) works well if the object can be divided using a single plane, otherwise SLICE > Surface may be a better option. There may be other options as well such directly modifying the existing Solid (ie SOLIDEDIT > Offset Faces eg.)

 

If you post a drawing, or at least a screenshot, we might be able to provide more specific help.

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Seeing the part would be a big help in giving you suggestions to edit the part.

 

If the portion of the model that needs to be changed is somewhat localized you can remove that portion through the use of the Boolean operations Union, Subtract, and Intersect. Consider the following process.

1. Create a box that covers the portion of the model that needs to be modified. The box should extend beyond the bounds of the part but not cover much of the part that will not change.

2. Make a copy of the original part and the box some know distance away (e.g., 100 inches to the right).

3. Use the Subtract operation on the first copy of your object and box to subtract the box from the object . This will yield your original part with a box shaped hole in it.

4. Use the Intersect operation on the second copy of your object and box. This will yield the piece of the original part that has been subtracted.

5. Edit the result of step 4 or create a new version of this piece to be unioned back into the result from step 3.

 

This is much easier to understand with a few pictures.

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nestly: I'm getting that it's probably easier to cut it apart by pieces. At least then I might be able to go at it a little easier from there.

Irm: I'm not quite following, but I'm sure it makes more sense than my frustrated brain lets it. :P I'm going to read through it slow and try to take it in steps.

Thanks, so far. I'll pipe up on whether it not I manage anything.

Until then, the file https://www.dropbox.com/s/4ba6vkdpbm90x1q/minicross%20WIP.dwg?dl=0

On Dropbox, because it's too big for this.

 

For reference, what I did was shrank it, then stacked it a few times to make it relatively thicker, because it wouldn't stretch at the time. It will have further editing from there. I need to remove out the shapes left inside, but not outside, and replace them with smoother, easier-to-print-around ones.

[url=https://www.dropbox.com/s/4ba6vkdpbm90x1q/minicross%20WIP.dwg?dl=0][/url]

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Here's a visual example of the technique I tried to describe above.

 

Let's say I have the robot shown in the left image and it is all one solid part and I would like to separate the arm from the rest of the robot. I cannot use slice because that is limited to a flat plane. The arm is connected to the cone shaped torso of the robot.

The second image shows the addition of a truncated cone (cyan colored) that matches the torso of the robot, a box that completely encloses the head and another box that completely encloses the legs. These two boxes and the cone are unioned together.

A copy of the robot and boxes/cone is made.

The third image shows the result of subtracting the cyan solid from the robot yielding just the arm.

The fourth image shows the result of using intersect on the copy of the two objects to yield the robot without the arm.

 

A similar technique could be used to isolate parts of your solid model that need to be modified.

Robot-Booleans.JPG

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@MathU41 Switch to Front, Back, Left or Right View(UCS) and slice through your object above the lower features and then again below the upper features. Erase the center portion, then use Extrude Faces on the Solid Editing toolbar/Ribbon to extend the lower portion up fill up the void. Then re-UNION if desired.

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Ouch, that hurts!:lol: I thought slice was limited to flat planes and thus my approach of using solids and Booleans. I was trying to show an approach that required something other than a flat plane. Now I know you are not limited to infinite flat planes and can use other objects.

 

I just tried slice with my robot example and had mixed results. I created a revolved surface as the slicing object and it did cut off the arm but also cut the arm into two pieces. Here's an exploded view of the result.

SLiced-Robot.JPG

The conic surface was flush with the robot torso when I gave the slice command. I expected the full arm to be one separate part. Instead, the shoulder and a finger tip were one part and the arm a second part. Why?

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I wish now I had saved my version of slicing with a surface because I removed the whole arm in one fell swoop using a surface created with two arcs that I lofted.

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@lrm You could just copy your robot off to the side then Explode it. You'd likely end up with a surface that you could then trim up and use to slice off the arm without the slice interfering with any other portion of the model. Also you can often use SUBOBJECT selection on a copy of the original to remove/delete adjacent faces, leaving only the objects you need.

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