topic Re: 3D modeling question in AutoCAD Forum

3D modeling question

BillAllenSE — Mon, 27 May 2024 15:26:08 GMT

O.K., I'm back playing with 3D again.
I'm trying to do something I think should be simple.
I have a ridge beam which is level to the world.
I'm trying to attach a valley beam which is 45 degrees from the ridge beam in plan view and is sloped 13.26 degrees downward. The problem I have, no matter which UCS I use, the top face of the valley beam is not level with the top face of the ridge beam, which they should be. The valley beam must be vertical and not rotated about its local axis.
Any ideas what I might be doing wrong?

Re: 3D modeling question

AVCPlugins — Mon, 27 May 2024 15:35:09 GMT

I don't see any errors in your model. Everything is exactly as it should be.

Re: 3D modeling question

AVCPlugins — Mon, 27 May 2024 15:40:00 GMT

Perhaps you want the roof covering to lie on the entire end of the beam, not on the edge. Then you need to slightly raise the beam and trim its upper end so that the section of the beam becomes not rectangular, but slightly beveled. But I think in real life no one will bother with this.

Re: 3D modeling question

BillAllenSE — Mon, 27 May 2024 15:56:54 GMT

The problem is, if the section is rotated about its own axis, it isn't as strong.

Speaking of trimming the ends, what is the best way to do that?

Re: 3D modeling question

AVCPlugins — Mon, 27 May 2024 16:33:20 GMT

To cut solids, use the _slice command at three points

Re: 3D modeling question

ChicagoLooper — Mon, 27 May 2024 17:21:12 GMT

Hi @BillAllenSE

Thanks for uploading your drawing. It makes it easier to understand your issue. And easier to explain what's going on.

1. I recommend rotating your objects by putting in the correct orientation with respect to the Earth's (ground) surface. When the UCS icon (x,y,z) is colored, you're in a 3D drawing environment. When it's white you're in 2D. As it is now, both you're joist and rafter are lying flat on the ground. The Viewcube displays FRONT.

Image-1

<<Your bean and rafter on the left and a recreated version is on right.>>

2. Rotate your objects (or redraw them) so the the joist is on the ground and the rafter is coming out of the joist at a 45-degree angle and pointing up towards the sky. Notice the VIEWWCUBE in upper right. Using the VIEWCUBE, change from Top to Front view.

Image-2

3. You can also click on any corner of the viewcube to get an orthographic view. Notice how Top, Front, and Left sides of the viewcube relate to the joist and rafter.

Image-3

<<Joist and rafter on the left means the building will be lying down. On the right, the rafter is above ground like it should be.

3. A surefire way to drawing with the correct orientation is to define your UCS using 3-Point. If you can click your mouse 3 times, you can temporarily define a new UCS. Click at (1) origin, (2) positive X direction, and (3) positive Y direction. In your case origin at bottom corner of joist, use midpoint or end point for positive X, and top corner of joist for positive Y. Then draw a vertical rafter (or horizontal rafter) then rotate the rafter 45-degrees. When you're finished, be sure to click the WORLD icon to end your temporary UCS and return to World UCS.

Image-4

5. It's also helpful to use Parallel view (not Perspective) when drawing. Perspective is nice for display and printing. Parallel will eliminate distortion. Right-click the House icon next to the ViewCube then select Parallel from the shortcut menu.

Image-5

Note:

There are other ways to draw in 3D. This way, although less efficient than other ways, is a surefire way to see what's going on when creating 3D objects and their relative to orientation to the ground (or what's up & down and what's left & right).

Re: 3D modeling question

leeminardi — Mon, 27 May 2024 19:23:41 GMT

I agree with @AVCPlugins , our construction is correct. I've added a sligt cylindrical bead to te top edge of the valley beam so that you can clearly see that the edge is flush with the ridge beam. If you subtract the ridge beam (of a copy) you'll get the correct trimming angles for the valley beam.

Re: 3D modeling question

Washingtonn — Mon, 27 May 2024 19:30:58 GMT

The top face of a beam perpendicular to the ridge can end up at the top face of the level ridge beam but since you are incorporating a second beam angle, the compound angles make it impossible. The only solution will be to trim at the intersection of the beams which may not be what you want to see or hide the condition in the field by using steel hardware or sheathing material.

Re: 3D modeling question

BillAllenSE — Mon, 27 May 2024 20:26:25 GMT

This is the result I'm attempting to achieve. However, I get a rotation of the valley beam. In my mind, where the valley beam meets the ridge, it should do that at both vertical faces of the valley beam. I rotate the valley beam twice, once for the slope of the roof (4/sqrt(2):12 or 13.26 degrees) and once for the skew (45 degrees). Both times I am rotating (3D Rotate) while in WCS.

This is driving me mad!...and keeping me from wanting to spend much time in 3D.

If I rotate about the z axis 45 degrees for the skew, it comes out right.

Or, if I rotate about the x axis 13.26 degrees for the slope, it comes out right.

But, if I do both, the top edge where it intersects the face of the ridge beam is not parallel.

Re: 3D modeling question

BillAllenSE — Mon, 27 May 2024 20:44:38 GMT

Thanks!

Re: 3D modeling question

BillAllenSE — Mon, 27 May 2024 20:51:25 GMT

...although the vertical edge where it intersects the ridge beam IS vertical:

Re: 3D modeling question

leeminardi — Mon, 27 May 2024 20:55:03 GMT

The circled edge of the valley beam is parallel to the top plane of the ridge beam. Your construction is correct! Just trim the valley beam with a subtract.

Note in the image below how the valley beam meets the ridge beam and that the cut end is not parallel to the edge of the ridge beam.

Re: 3D modeling question

AVCPlugins — Tue, 28 May 2024 02:26:11 GMT

By the way, to cut off the extra ends of beams that get inside other beams, you can simply subtract one beam from another with the _Subtruct command. But this command has a drawback - it always destroys the subtracted solid and you have to make a copy. There is an AVC Drill plugin that has a Gap command. This is the same subtraction but without removing the subtrahend. And with this command you can make grooves (dadoes) with a gap.
The AVC DadoJoint plugin may also be useful in your project.