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Author: Subhamoy Sengupta
Hello and welcome to this tutorial on hard surface modeling in Modo! Even if you have learned how to handle and edit primitives well, modeling even some regular everyday objects sometimes present us with problems that take time and planning to solve. Today we will look at several such problems.
Problem 01: Filleted Intersections
Here, the rings are smooth, but the transition between the rings and the connectors is hard. If those connections are welded, this is not how it should look like.
So we will pick only a piece of the pie. There are 6 connectors and 24 segments in each ring. We will keep only one connector and 4 segments from each ring. It will be make things easier if the connector intersects the same number of polygons on each ring.
Select at least 2 poly’s of each poly ring you want to keep, and hit L. Press [ to invert selection and hit DEL to remove all selected polygons. Now switch to the other mesh item and delete all connectors except the one connecting these two pieces.
With the rings mesh item above the connectors mesh item and rings mesh item selected, run GEOMETRY > BOOLEAN > SOLID DRILL and choose SLICE mode. Repeat it with connectors mesh item above rings mesh item while connectors mesh item is selected. What this will do is, it will cut edges along the intersection on both mesh items. Press C for Edge Slice Tool
and connect vertices on the newly created n-gons to keep everything quad. Finally, delete the polygons beyond the solid drill cut lines.
Cut one of the mesh items and paste it into the other mesh item. Now that they are all one mesh, run VERTEX > MERGE TOOL.
1mm worked for me. But depending on the size you chose, it may vary. Double click on the connecting edges to select them all. Press B and click drag on view port to perform edge bevel. Keep the beveling low and keep Sharp Corner checked. This will keep the definition tight when we change to SubD.
Change action centre to Origin, and perform DUPLICATE > RADIAL ARRAY. Since we would have no further use for this piece, check Replace Source. Also check Merge Vertices. Set Count to the total number of pieces we want. In this case, it’s 6. Finally, hit TAB to switch to SubD and now it all looks like one piece.
Problem 02: Grooves on a Screw
Let us create a cylinder primitive. The segment count may look insane right now, but soon it will make sense. Delete the top and bottom cap and press Shift +T to triangulate the mesh item. See the new edges thus created flowing down in a spiral fashion? Choose such an edge spiral and select the first few vertices on it and press and hold UP ARROW to make Modo perform a heuristic ‘Select More‘ until the whole cylinder is traversed. Press Shift + O to convert this selection to a curve. Now we can delete all the polygons.
Unfortunately, Modo does not have any curve simplification tool. So we will have to create polygonal geometry and simplify that. In Polygon selection mode, click on the spiral, press X for Polygon Extrude Tool and click on view port to activate the tool. Pull up until there is just no gap left. Run VERTEX > MERGE TOOL. If you are working in real world scale, then something very small like 10 um will do it. Right now, each edge ring has 168 edges. Comparing to a default cylinder primitive, that is 6
times too many. So we will remove every six edges after one edge to keep the edge count manageable. For that, begin from any end and select every 7th edge a few times and then press and hold the UP ARROW till the whole cylinder is traversed. Hold down Shift and select a few edges on the spiral flow and hit L to select all of those. This will select what we want to keep. Now hit [ to invert the selection. Now press BACKSPACE to reject what we no longer need.
Double click on any of the polygons to select them all. Do an edge slice (Alt+C) with Count = 2 and Mode = Symmetry. About 20% will do. Loop select the larger polygons, press B for Polygon Bevel Tool. Bevel them out with Group Polygons checked. The blue direction handle will pull them out. The red scale handle will scale them down.
Select the open edges of the spiral flow, press Z and click on view port for Edge Extend Tool. Move up above the grooves, press R to switch to Scale Tool, and input numeric value 0% in Y to level the edges.
Make some cuts and push the few end edges of the groove in so that the end of the groove gradually blends in. Performs a vertex merge and repeat this for the bottom. Loop select the beveled polygons and slice them close to the outer edge of the groove. This approach leaves 2 pentagons on the mesh, which shall pose no trouble whatsoever. Switch to some orthographic view for convenience, draw out a linear falloff. To do this, click at the bottom of the screw and pull up by the gizmo. Do not drag freely or it will not be perfectly vertical. The thick end of the handle signifies maximum effect. The other end is minimum. With the falloff still selected, press R for Scale Tool and use the side handle to adjust to your liking. It will be either X or Z handle. When you are done, just copy the numeric value of that axis to the other horizontal axis. Finally, just press TAB to switch to SubD.
Problem 03: Head of a Bolt
Again, let’s take a cylinder primitive. This time with 6 sides and one height segment only. Delete the top cap. Select the top edge loop and do a loop slice (Alt + C) with Count = 3 and Mode = Uniform. Select the top edges again and edge extend (Z). Scale the edges in. Loop slice the new polygon ring with the previous settings.
Keep just the upper cap with the hole and delete everything else. Switch to top view (Numpad 1) and draw out a Radial Falloff from the centre of the object. It’s easy to check from the numeric values if it is a perfect circle. Set the radius of the falloff such that it pans slightly more than the cylinder. Now switch back to perspective view (Numpad Period) and move up with the Move Tool (W) until it somewhat resembles the shape of a tent. Hit SPACE to drop the move tool and then Press Esc to remove the falloff.
Switch to top view again and draw a much smaller radial falloff. There is no need to be extremely cautious about the size. We can always adjust it later. This time, move down until there is a decent bit of curvature. Drop the falloff and select the innermost edge loop. With scale tool, level them out as we have done many times previously. Take a sphere primitive within the same mesh item. Now our cap has 24 sides, and so does a default sphere. In top view, size the sphere up. Move it up so that its equator aligns perfectly with the leveled edges of our bolt head. Delete the upper hemisphere of the sphere and flip the
polygons of the lower half (F). Now choose VERTEX > DRAG WELD and drag bolt head vertices to merge with the sphere vertices.
Important: When you drop a sphere primitive, it is in SubD. Do not forget to select the sphere polygons only and press TAB to
switch back to polys before welding.
If we press TAB to switch to SubD, we shall see the transition is too soft and rounded. We want something harder, but we do not want to keep adding more and more loop slices. So we will select the transition edge loop and choose VERTEX MAP > EDGE WEIGHT TOOL. Click on view port and drag to about 70%. Going too high will make the edges look abnormally hard
and also make artifacts appear.
Select the lowermost edge loop, extend down (Z) and level them out. Extend again and scale in. Use the edge weight tool again to define the corners of the bolt. But trying to harden the bottom edge will cause weird creases. So we can’t use edge weighing there.
So we will cut an edge loop there to hold the shape better. Now, inside the half-sphere, if we choose a pair of facing polygons and POLYGON > BRIDGE them, they will look too smoothed out in SubD. But using hard edge will cause creases there as well. Instead, we will try hard polygons.
So, select the polygons on the bridge. Press Shift + W, click on view port and drag. And that finishes the bolt head.
Problem 04: Making Holes
Hold down Ctrl and click on the cube primitive button. That will create a default sized cube. Subdivide it in faceted mode once. Press Shift + T to triangulate the box. But the orientation of the new edges are wrong. So, take any one face of the cube and double click on all 4 diagonals to select all the new edges. Press V to spin them. Now they are the way we need them.
Select the centre vertex of every face and bevel them (B). This will create 3 pairs of facing octagons. Select each pair at a time and bridge them. But we have a problem. The bridges are getting into each other’s way. So we can’t see through. Select all the cube face polygons and press H to hide them. Select the bridge polygons and press F to flip them.
Select any one of the 3 bridges, cut it (Ctrl + X), create a new mesh item and paste (Ctrl + V). Now, with this new mesh item selected, run GEOMETRY > BOOLEAN > SOLID DRILL in Slice mode. Now cut and paste it back to the previous mesh item. Repeat this for the other two bridges, or delete those two bridges and duplicate/rotate this bridge twice to make up
for them. Either way works fine.
Now that the bridges have drilled onto each other, we can delete the polygons that were getting in the way. When that is done, select all the visible polygons on screen and flip them back. Now press U to unhide the face polygons of the cube. Finally, run the VERTEX > MERGE TOOL and add some weight to the corner edges. Hit TAB to get
this interesting shape:
And that concludes this tutorial. Thanks for reading through. For any questions or comments, feel free to write me at firstname.lastname@example.org