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TUTORIAL II

A Cylinder With Rounded Corners


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Step 1 - Creating the Top and Bottom Corners

Add a primitive disk. Set the properties to Radius=10 and Sections=32. Pick Object Select mode and the Marquee Selection tool. Select the disk by dragging a rectangle around its axis. Select Transformation from The Object menu and check the Position check box. Type in 40,0,40 for X,Y,Z. With the Disk still selected bring up the Object Transformations dialog box again (TIP: Hold down the "ALT" key then press "o" followed by "t"). Check the Position and the Transform Axis Only check boxes. Type in 0,0,0 for X,Y,Z. This operation moves the axis back to the center making the next operation easier. Select the disk again. Copy it then paste it. Without selecting anything else bring up the Object Transformation dialog box. Check the scale check box and type in 1,1,-1 for X,Y,Z. This operation mirrors the disk around the Z axis putting it in the correct position for the bottom corner (People with the most recent version of IFW can use Mirror around the Z axis). Now, using the Object Selection mode and the Marquee selection tool drag a rectangle around the object's axis selecting both of them. Pick Join from the Object menu. We now have the two disks as one complete object.

Select the disk object and pick Point Selection mode and the Marquee Select tool. Initially select the center point of the top disk, in the FRONT view. Then, hold down the "SHIFT" key and pick the center point of the bottom disk. This is shown below in Figure 1. The "SHIFT" key is the MULTI select key allowing multiple selections to be done individually. Delete these two points. Using the Marquee tool drag out a rectangle, in the FRONT view, which compasses the points on the left of each disk. Delete these points. This is shown below in Figure 2, make sure that the points at exactly 12 o'clock and 6 o'clock on both disks are NOT selected. Again in the FRONT view, drag out a recangle which encompasses the points in the lower half of the top disk and the upper half of the bottom disk. Delete these points. This is shown below in Figure 3, make sure that the points at exactly 3 o'clock on both disks are NOT selected. We now have the corners for the cylinder so select them in Object Select mode and save as cylcorns.iob.

Step 1 Figures

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Figure 1
Figure 2
Figure 3


Step 2 - Adding the Top, Bottom and Sides for the Finished Profile

Load cylcorns.iob, if not already loaded. Initially select Size from Grid in the View menu. Type in a grid size of 10. Select the corner object in object select mode and then Lines from Add in the Mode Menu. Firstly, we are make the edge which will form the side of the cylinder by clicking on the lowest point of the top corner then the highest point of the bottom corner. This is shown in Figure 4. Press the "ESC" key to start the construction of a new line. To form the top edge click on the left most point of the top corner, notice that it changes the point colour, and then at a point directly above the axis and horizontal to the first point. Don't worry about being too precise with the second point. The bottom edge is added in the same way, again press the "ESC" key to start a new line. Then click on a point on the left most point of the bottom corner and then a point directly below the axis and horizontal to the first point. These edges are shown below in Figure 5.

Finally to complete the profile of the cylinder pick Point Select mode and select the two most left points on the top and bottom edges, in the FRONT view. Then pick Snap to Grid from the Functions menu. This operation snaps the top and bottom edges into the right position, as we correctly set the grid at the start. We have now completed the rounded cyclinder profile, so select it in Object Select mode and save as cylprof.iob

Step 2 Figures

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Figure 4
Figure 5
Figure 6


Step 3 - Spinning the Complete Cylinder

Load cylprof.iob, if not already loaded. Select the cylinder profile in Object Select mode and bring up the Sweep Controls dialog box GIF. The properties for the sweep are Sweep Angle=360 and Number of Sections=32. We now have the complete cylinder with rounded edges, see Figure 7 below. Select the object and save it as rndcyl.iob.

Step 3 Figures

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Figure 7


And Finally.......

There is a much easier way of creating this object. This is using a similar principle to Step 1 in the Rounded Box Tutorial. Imagine, (sic!) a disk rotated in the same manner as the cylinder, then remove the center point and re-position the corners, as described in Step 1. Then, delete the points on the left to leave the reversed flattened 'C' profile. All that is left to do is positioning the axis correctly for the sweep and voila!

The ideas described above can be extended further. For example if you wanted a hole running through the middle, think of the profile. This would be a 'O' shape with flatten sides and the axis to the left. The distance between the axis and the left edge would be the radius of the hole. This is shown below in Figures 8 and 9. Again the flatten 'O' is reminisent of the shape generated in the Rounded Box tutorial. Also, this type of procedure can be used to create profiles to extrude, although there is the issue of the end caps.

Final Figures

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Figure 8
Figure 9

This form of modelling is a one of the most useful as so many objects can be created by this method, either swept or extruded.

There is a common theme running through the tutorials, that is, the saving of objects after each modelling stage. This is very important in case any mistakes are made or if things don't look right. You can then simply go back to a previous object or profile and try again.


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© Richard Jennings 1997, 1998