Cheetah 3D Tutorial: Modeling a T-Junction

tutorial_tjunction_title
The finished T-junction model.

One aspect of modeling that I didn’t anticipate is that will turn you into a keen observer. To make a believable model you must have good reference material – but also curiosity and an appreciation of how things are put together. Every artifact is designed by someone, and many day-to-day items that we take for granted can rise to the level of art when you look at them closely.

A T-junction may not fall into this category, but it’s still a workmanlike bit of design that gets the job done. It will provide a decent modeling challenge that involves creating and combining several meshes and working with many of Cheetah’s modeling tools. Let’s try to do it justice.

T-junction
A fine Malleable Iron T Style Conduit Body, featured on the Garvin Industries website.

Here is what a T style electrical conduit looks like. In our scene, it will be connected to conduits, so we’ll be leaving out the inner threads on the joints. But we’ll try to make the rest of it as accurate as possible.

For this tutorial you’ll need a basic familiarity with Cheetah 3D: How to create objects, use the Object Browser, navigate around the 3D view, and use the Transform tool. We’ll use the Transform tool’s Snapping settings so we can work quickly and accurately, so take a couple of minutes to review how those work if you haven’t used them before.

Here are the tools we’ll be using. They can be found in the main Tools menu, and also in the context menu that appears when you right click anywhere in the 3D view. A top priority will be to end up with a mesh consisting entirely of quads – four-sided polygons – because they subdivide more evenly than other types of polygons.

Ready? Let’s get started.

Starting the scene

Start a new file and save it as tJunction.jas (or whatever name you prefer). Create a cylinder 2 units high, with 20 longitudinal sections, 6 height sections, a radius of 1, and no covers. Select Transform, with Snapping set to Raster with a raster width of 1.0. (This will snap any movements to the grid in one-unit increments.) Move the cylinder two units in the negative X direction. With the cylinder selected, select Objects > Make Editable, or simply double click the cylinder icon in the Object Browser. In the browser, rename the resulting mesh “Main.”


Switch to the Front view and, in Polygon mode, use Area Select to highlight the polygons on the right side of the mesh. Delete them.


Switch to the Left view, highlight the polys on the left and bottom halves and delete those, too.


Your mesh should look like this. We’re going to take advantage of the fact that this object is more or less symmetrical in all three dimensions. We’ll start with a single corner and then use Mirror to build it back out, greatly reducing the amount of work we have to do.


Highlight the right vertical edge and select Cover, then use the Transform tool to drag it to the right. If snapping is still enabled, the edge will snap right to the Z (blue) axis.


Use Ring Cut to add five new edges.

Creating the joints

Create a second cylinder 1 unit high, with 16 longitudinal sections, 1 height section, a radius of 0.75, and no covers. Move it away from the main mesh. Make it editable and, in the Object Browser, name it Joint1. In Edge mode, use Loop Select to highlight the top, circular edge.


We’ll extrude this inward to create a lip on the cylinder. There are a few ways to do this, but this may be the quickest:

  1. Select Cover and then Transform. Disable Snapping by setting it to None.
  2. Tap one of the box-shaped scale widgets on the Transform tool (it doesn’t matter which one).
  3. Click the small sphere at the tool’s origin. While holding the left mouse button down, drag to the left to extrude the edge inward.


Highlight the edge again and select Cover. Use the Transform tool to extrude it slightly down into the cylinder. Additional edges will be needed later when the mesh is subdivided. We’ll add them now to save a few clicks later. Select Ring Cut and add five additional edges.


Switch to Object mode, select Joint1, then copy and paste to duplicate it. Name the second copy Joint2. Rotate Joint1 to the left by setting its bank value to 90 in the Rotation section of the Properties panel. Rotate Joint2 forward by setting its pitch value to 90.


With the Transform tool selected, set Snapping to Raster and the raster width to 0.5. Move Joint1 into position.

Merging the meshes

Now we’ll combine Main and Joint1 into a single object. The tool you use for this varies, depending on which version of Cheetah you are using.

Version 6 or earlier:

  1. Drag and drop Joint1 on top of the Main object in the browser, so it is nested beneath it.
  2. Select the Main object, and then Tools > Import Children.
  3. Delete Joint1. Its shape should remain, copied into the Main object.

Version 7: In Object mode, highlight Main and Joint1 in the browser and select Tools > Merge.


Switch to Left view, highlight these polys and delete them.


Now go into Point mode. You’ll see dozens of stray vertices in the 3D view. These are left behind whenever geometry is removed, and it’s a good idea to clean them up from time to time. We’ll do this with Optimize, which also fixes small breaks in the mesh by merging vertices within a certain threshold. With the object selected, go to Optimize. The default threshold is 0.001; it’s best to leave it there. Click OK. The extra points will disappear.

Now we’ll merge the combined shapes into a single mesh.


Switch to Top view. One at a time, select the inner vertices and – moving them in the X direction – line them up with the curve of the main mesh. Be sure Snap is disabled. If the grid is distracting, turn that off, too. It may also help to switch the view to wireframe, as shown here.


A couple of vertices need to be adjusted to prevent uneven tension when the mesh is subdivided. Select the vertex indicated here in Perspective view, but move it in Top view, being careful to keep it lined up with the shape of the curve. (Working in Quad view here helps to keep an eye on things.) The vertex above and to the left of this vertex can also be nudged as needed. Just be sure to keep it on the curve in Top view.


Select Scalpel and cut around the cylinder shape.


Highlight and delete the polygons behind the cylinder.


Use Create Polygon to fill in the gap and link the meshes together. Be sure to click on existing vertices so all the polys are connected, and work in a counterclockwise direction so the polys all face outward. When you are finished, optimize the mesh again to weld any overlapping vertices and delete stray ones.


Use Ring Cut to add another edge.

Time to mirror out the back side of the mesh.

  1. Go into Pivot mode (click the icon to the right of Object mode in the toolbar) and move the pivot to the grid origin. Enabling snap to raster will make this easier.
  2. Select Tools > Coord System and click Burn Pivot Point to make its new location permanent.
  3. With the Main mesh selected in the browser, switch to Polygon Mode, but make sure that no polys are selected.
  4. Select Tools > Mirror, and set the mirror plane to Z. Leave the other settings at their default values. Click OK.
  5. Optimize the mesh.


Now, move Joint2 into position and merge it with the main mesh, as you did with the first one.


Switch to Front view, and highlight and delete these polygons.


Select the vertices on the inside edge and snap them to the surface of the main mesh.


Check the positions of the vertical edges on the Main shape behind the cylinder, and adjust them.


Use the Scalpel tool to cut around the cylinder.


Select and delete these polys, and use Create Polygon to link the two meshes. Optimize the mesh when you’re done.


Add a new ring cut.

Switch to Polygon mode, again making sure that no polys are selected. Mirror the object in the X direction. Optimize the mesh.


The front cylinder seems a little stubby, so let’s fix that. Go to Top view and Point Mode, and use Area Select to highlight the first two rows of vertices. Select the Transform tool and move them out to about 3/4 unit.

Bottom surface

We’ll get to the bottom edge indirectly, by first adding an inner ring of polygons to the top. Select the top edge of the mesh and, as we did with the cylinder, use Cover and the Transform tool to extrude it slightly inward.


The underlying shape’s proportions cause the new edge to be wider on either end. This can be fixed by scaling it back out slightly in the X (red) direction.


Switch to Polygon mode and make sure no polys are selected. Mirror the object in the Y direction. Optimize the mesh.


Move your view to the bottom of the mesh. Select Fill Hole and click an edge vertex to fill the remaining space.


Use the Scalpel tool to cut the resulting n-gon in half, along the Z axis.

Switch to Top view, select the polys as shown, and delete.


Back in Perspective view, divide the n-gon in the short direction with the Scalpel tool.


Cutting the resulting polys in the long direction is problematic. Because Cheetah’s Scalpel tool does not allow you to cut more than one poly at a time, it’s difficult to get a truly straight edge. Here’s a workaround: Delete the remaining n-gon, then use the Ring Cut tool insert three edges across the remaining polys.


Select the center edge and, in Bottom view, snap it to the X (red) axis.


Then use the Create Polygon tool to fill in the gap. Optimize the mesh and add new edge rings as shown.

Top surface

Movie your view back to the top of the mesh. Create a Plane object 5 units wide and 1.5 units deep, with 16 sections width and 6 sections depth. Make it editable.


Position it slightly above the main mesh, then select and delete the polys as shown. Optimize.

Switch to Top view and highlight these polys. Select Jigsaw, then click any of the highlighted edges. Drag to adjust the location of the resulting edge.


Add these additional edges with the Scalpel tool.


Now delete these edges . . .

and move the corner vertex inward to create this corner shape. Note that all the resulting polys are quads – this will help ensure a smooth subdivided mesh later on.


With the plane selected, go to Polygon mode and make sure no polys are selected. Mirror it in the Z direction and optimize. Switch to Object mode and, with raster snap enabled, move the plane down until it aligns with the top of the main mesh.


Highlight these polys and use the Transform tool to move them 0.3 units in the positive Y direction. (Set Snapping to Raster, and raster width to 0.1.)


Use Ring Cut to add two more edges.


Use Import Children or Merge (depending on your version of Cheetah) to merge the plane with the main mesh. Mirror the mesh in the X direction. Optimize.


Select Bridge and click a vertex on the outside edge of the plane, and a second vertex opposite it on the main mesh. This will fill in the gap with quads.


Add a new edge as shown.

Adding the seam

One more detail needs to be added to the main mesh: the seam between the cover and the main body. This will take just a few steps.


Select all the polys on the top edge and use the Cover tool to extrude them vertically by a unit or so. An easy way to select all of them is to switch to Front view and use group select as shown here.


Use Ring Cut to add five new edges.


Use Ring Select to select all the polys between the cover and main body. Select Cover and then the Transform tool. While holding the Shift key down, click the Y scale widget (the green box) and, while holding down the mouse button, drag left. This will extrude the selected polys inward. Click the X scale widget (red) and drag out to equalize the amount of the extrusion.


Add four more edges: two at the bottom edge of the large polys (shown here), and two similar edges at the top of the large polys.


Select all the top cover polys again and move them down, leaving only a small gap between them and the main body.

Screw heads

The final touch will be adding the heads of the two screws that hold the cover in place. This will be quick!

Create a new ball object and move it away from the origin so you can work on it. Change the Sections Longitudinal to 16 and the Sections Parallel to 11, and leave the other settings at their default values.


Change the ball’s bank rotation to 90 degrees and make it editable. Select Tools > Coord System and click Burn Transform to make the rotation permanent. Click Center Pivot Point to, well, recenter the object’s Pivot Point (which moves to the grid origin when Burn Transform is used). Then select the polys indicated here.


Select Cover and then the Transform tool, and extrude the polys in the positive Y direction by a unit or so.


Click the Y scaling widget (green) and drag down to flatten the polys.


Select and delete the four polys on either end of the extrusion.


Select the four remaining extruded polys and move them back down so they line up with the bottom edge of the slot. Patch the gaps with the Create Polygon Tool. (Tip: Use Create Polygon to create the center poly on each end, then Fill Hole to complete the other four.)

Switch to Left view and delete the bottom half of the ball. Optimize.


Select the Transform tool and scale the ball vertically to squash it.


In Perspective view, highlight the edges around the slot, including the two inside edges.


Then select Bevel. Change Level to 1, leaving the other values at their defaults, and click and drag anywhere in the 3D view to adjust the bevel width.


Select the bottom edge. Just as we did with the cylinder, use Cover and the Transform tool to add two or three concentric rings of polygons.


A small detail: Select every other edge on both poles, and delete them. This converts the triangles into quads, which will subdivide much more nicely.


Switch to Object mode and select the mesh, and then the Transform tool. Tap any one of the scaling widgets, then click the center sphere and drag to scale down the mesh.


In Quad view, move the mesh into position and tweak the scale as needed. Once you’re happy with the size and location, select Tools > Coord System and click Burn Transform, then click Center Pivot Point.

In the browser, copy and paste a new copy of the mesh, then move it into position on the other side of the T junction. Use Import Children or Merge to combine the two screw meshes with the main mesh.

Subdividing the mesh

Select the mesh in the browser, then select Objects > Modifier > Subdivision. The default setting of 2 will subdivide each quad in your mesh twice: Each quad will become eight quads. The resulting mesh is much smoother and should render nicely.

To make the subdivision permanent, double-click the Main mesh icon in the Object Browser. You may need to do this, for example, in order to export a high-resolution mesh for use in other software packages.

It’s a good idea to save a copy of the low-poly version, for editing or re-use later.


Here is a quick rendering of the final model.

Congratulations! Compare your rendering to the original object pictured at the top of this post. As an extra challenge, create and apply materials to make your rendering more realistic.