Autodesk Mechanical Desktop: Keeping to the Straight and Narrow
By Bill Fane
During the last few tutorials we have been working through the various 3D sweep paths available in Autodesk? Mechanical Desktop? software. This time we will cover the last two variants.
The good news is that I have run out of goofy "There are four kinds of sweep path..." introductions. The bad news is that I have not run out of bad jokes, such as "There are two kinds of people in the world; those who divide things into two categories and those who don't." 3D spline sweeps are great for creating free-flowing features like hoses and cables, but what if you want a 3D sweep to contain straight sections connected by fixed-radius curves? (Hey, that sounds a lot like a description of the piping shown in Figure 1.)
Figure 1: A section of 3D piping.
No problem. The process is very similar to that used for 3D spline sweeps. It requires just four simple steps: 1. Use the standard 3DPOLY command and create a 3D polyline. Define vertices by typing in coordinate triplets (x,y,z), by using object snaps to existing geometry, by using standard DDE (Direct Distance Entry) procedures, or a combination of the three methods. Figure 2 shows a sample 3D polyline. Don't worry about the radii to be used for elbows because a 3D polyline cannot contain arc segments anyway. This will be handled later.
Figure 2: A standard 3D polyline.
2. Start the AM3DPATH command and enter the Pipe option. When prompted, select the 3D polyline. In fact, you can select more than one polyline so long as they touch end-to-end to form a single, contiguous path. When you have finished selecting 3D polylines, you are prompted to select a start point near one end of the path.
Similar to the 3D spline path, a spreadsheet dialog box now automatically displays (see Figure 3). The function of each column in the spreadsheet should be obvious from the headings.
Figure 3: 3D Pipe Path dialog box.
There is a significant difference between the x, y, and z values in this table compared to those for the 3D spline paths we studied last time.
For a 3D spline path the values are relative to the origin of the sketch plane that was active at the time it was created. But for a pipe path the sketch plane determines the directions while the values are relative to the previous point.
You can edit any value at this point, and the path adjusts accordingly. If you change a value, succeeding segments move in order to remain horizontal and vertical. As indicated in step 1, here is where you can add radii at the corners. For now, let's leave the corners sharp and the vertices where they are. 3. When you click OK to continue, a work point and a work plane are created at the start of the path. You can now create a sketch, and then dimension and constrain it using usual Mechanical Desktop techniques (see Figure 4). Use two dimensions to tie the sketch to the work point.
Figure 4: The profile is dimensioned to the work point.
4. When you are ready, use the AMSWEEP command to sweep the profile along the path as shown in Figure 5.
Figure 5: The profile is swept along the path to produce the pipe.