Primitive Surface Modeling in Rhino

Screenshot

This workflow describes a method of modeling a doorknob from 2d drawings, and demonstrates the use of simple primitives and basic modeling operations in Rhino.
Uses Tool(s) Rhinoceros

## Step 1: Setup the Base Drawing

In order to begin your model you will need to draw a plan and a front view of the object with given dimensions. Once you complete the 2d drawings you are ready to begin your 3d modeling. Please take particular notice in organizing your model into layers, so that it becomes easier for you to select, hide and show objects and generally manipulate your model faster. The base drawing is created in centimeters.

## Step 2: Etxrusion and Cap commands

Working on the Perspective view , select the bigger circle of your drawing and enter in the command line: ExtrudeCrv and then press Enter . Before you click on the viewport, you will see a few options appearing in the command line. Whatever you wish to adjust, just click on the words on the command line and then enter the number of the extrusion length, which in this case will be -1.0.

The other options should be in this form: Direction BothSides = No , Solid = No , DeleteInput = No , ToBoundary SplitTangents = No

After completing the extrusion, enter the command Cap in the command line, then select your extruded surface and press Enter . A shorter way for the same result would be to select Solid = Yes in the extrusion command and skip the Cap command.

Follow the same procedure for the other 2 circles entering the values -1.3 and -1.8 respectively.

## Step 3 : BooleanUnion command

When you finish creating your extruded shapes you will end having 3 separate, homocentric cylinders. In order to join these 3 shapes into one we will use the Boolean command. Enter in the command line BooleanUnion , press Enter and then select the shapes you want to join.

## Step 4 : Extrusion of additional shapes

Follow the same procedure ( Extrusion see step 2) for the rest of the shapes, by setting the extrusion length of the curved shape to be -2.6, and for the shapes that create the handle to be 1.

Tip: After you finish with all the Extrusions you can hide some shapes of your model if they obstruct the manipulation of other parts of the model. If you wish to hide an object, simply select it, by clicking on it, type Hide in the command line and press Enter . If you wish to unhide the object you just hid, type Show in the command line and then press {cmd|Enter}}. Keep in mind that the Show command reveals every hidden object at the same time.

## Step 5 : Explode handle, Isolate the outer surface of the handle

Use the Explode command in order to isolate the outer, continuous surface on the extruded objects that compose the handle. Select the shape/shapes you want to explode and then type Explode on the command line and then press Enter . Select the surfaces that you want to keep and delete the rest.

## Step 6 : Fillet the edge of the handle

In order to smoothen the corner of this surface we will use the FilletSrf command. Enter FilletSrf in the command line and press Enter . Same as before, some options will appear in the command line. Set the Fillet Radius to be 0.5 by clicking in Radius =1.00, then enter your value and press Enter . Then select the 2 surfaces you want to apply the FilletSrf command. Join the 3 surfaces by selecting them and enter Join in the command line and press Enter .

## Step 7 : Offset surface command

After joining your surface, you will now create the width of the handle. Enter OffsetSrf in the command line and press Enter . Again a series of options will appear in the command line. Enter the value 1.0 as an offset distance and make sure that the arrows that appear on the surface point away from your surface, otherwise you will have to click on FlipAll in order to change the direction of the arrows. A solid surface will be created as soon as you press Enter .

## Step : 8 Setting a new Cplane to a surface

To complete the modeling of the handle you will have to create some detail in the shape of the handle that includes some basic manipulation of the edges and surfaces of your initial shape. First, use the Explode command, as before (see Step 5)to break your shape into the individual surfaces. In order to manipulate a particular surface correctly, you will have to set a new Cplane based on the surface you want to modify. First turn your snaps on by clicking Osnap at the bottom of your viewport. Then, select the surface shown on the screenshot below and click on the icon in the Cplanes tab, Set Cplane to surface . Click on the corner of the selected surface to specify the first origin point of the new Cplane, drag your mouse downwards or upwards and specify a second point on the same surface. You will see that the Cplane is set to your surface. In order to modify the surface, you will have to set the surface along with the new Cplane to Top View . In order to do that, click on the icon shown below in the Set View tab called Plan view of Cplane . Notice that your selected surface is now switched to Top View . Enter Scale2D in the command line, click on the surface twice to set 2 reference points and then drag to adjust the scale factor. After you finish with that set the Cplane to its original position by clicking the icon Set Cplane World Top in the Cplanes tab.

## Step 9 : Manipulate the edges of a surface

In order to complete the geometry of the handle you will have to manipulate the edges of your shape and close the gaps that are created from the previous scaling. Select one of the surrounding surfaces and enter MoveEdge in the command line and press Enter . Rhino will ask you to specify which edge you would like to move. Select the edge by clicking on it, set your Osnap on and check the Mid at the bottom of your viewport and press Enter . Then click on the middle of the edge you want to move and drag until you snap on the middle of the adjacent edge of the scaled surface. Follow the same procedure for all 4 surrounding surfaces.

## Step 10 : Trim command

You now have to trim the unwanted parts of the surrounding surfaces, which exceed of the boundaries of your final shape. In order to do that, enter the Trim command in the command line and press Enter . Rhino will then ask you to specify the Cutting object , which in your case are the above and underneath surfaces. Select the first surface, press Enter and then automatically Rhino will ask you to Select object to trim . Then click on the parts of the surfaces that exceed the boundaries of your shape. Then, redo the FilletSrf (see Step 6)command as before to smoothen the second corner of the handle.

## Step 11 : Final model of the doorknob

Select all the surfaces of the handle and enter Join in the command line and press Enter to get a unified shape. After that, your model is complete.

## Resources

Base Rhino Model
The Rhino model used in this workflow, with measured 2d drawings completed.

## Common Problems

Layers
Keep your model organized!
It is better not to use the Show command massively, because it doesn't keep track of a list of the hidden objects. In this way it reveals every object at the same time, even some objects that you don't wish to reveal at that time. Moreover, it is very common to forget the exact number of objects you have hidden. It is suggested to organize your model in Layers, so that you can control your model more efficiently.
Boolean operation
The Boolean command may sometimes fail to apply, mostly because the intersection of the shapes is not correct. To check if the Intersection is correct, select the two shapes and enter Intersect in the command line. Check if the intersection curve is closed, where if it isn't, you will have to find if there are gaps or overlaps in your intersection. To find gaps in your curve enter CrvStart in the command line.
Most problems with the Boolean operation appear in Coplanar surfaces, some Polysurfaces and Invalid objects (check for Invalid objects with the command SelBadObjects ).
In any case, if your Boolean operation keeps on failing, you can perform the Boolean operation manually, by using Intersect , Join , Split and Delete commands.