Intermediate Modeling: Walkway Frame Weldment
Using the weldment capabilities of the software can save you a lot of time. Here is an example of a simple frame.
(click to zoom)
This is a modification to an existing walkway. The circles show features used to attach a handrailing. If we ignore the circles, we end up with twelve pieces of metal.
Before weldments and multibody parts these would be modelled individually and you would end up with twelve individual parts. This drawing came from a DWG file, and it was done in 2D because that seems like the fastest way to construct this.
However, this can be handled very efficiently in 3D. Building it as a solid model has other advantages.
Let's follow our general methodology:
A. Preplanning Hierachy
If we model this as 12 individual parts we could worry about assemblies and subassemblies, but we will model this as a multibody weldment, so there will only be one part. We don't need to be concerned about a file hierachy.
Notice that the units are fractional, so we should set it up the same way. To set up fractional units, go to Tools>Options>Document Properties>Units. Pick "custom" then "feet&inches." Notice that the smallest fraction on the drawing is 1/16 inch, so we'll use that as the base fraction in the properties.
B. Origin and Orientation
We're looking down onto the platform, so this view should be on our top plane. Right and front could be determined by the orientation of the part in the final assembly, for our purposes set it like it is shown.
Setting the origin is a little tricky, as there seems to be no natural (0,0) on the drawing. If we assume that this is attached at the top, we could consider the upper rectangle to be symmetric and pick the origin at the top between the two vertical frame pieces (basically underneath the 3'-2 5/8" dimension).
C. Reference Planes and Auxiliary Geometry
This geometry cannot really benefit from reference geometry. However, if there was another assembly that attached to the bottom end we could place an auxiliary frame there.
Also, you can see that the walkway is shown extended as dotted, so we could consider providing some features (planes, or just an axis) so that the extended part has something obvious to attach to that is not part of the frame. The idea is to provide this independent of the frame, by drawing a layout, adding the reference axis, then building the geometry.
D. Modelling Planning
In order to use the weldment capabilities you want to start with a layout sketch. You then use the sketch entities to place weldment profiles along those edges. Note that all the dimensions are consistently drawing to the outside face of the C channel. Because everything is in the same plane, we can place everything onto a single sketch.
As far as design intent, it looks like this drawing may be overdimensioned. Because we're using fractions there is a good chance that the dimensions don't match exactly. You have to decide on the design intent. A good approach may be: assume that we have a given start point, but that the end point follows the length of the frame pieces. Assume that the width of the walkway is a controlling dimension. The 41.17 deg angular dimension should just be a driven dimension, because it's unlikely that somebody will build a frame to 1/100 of a degree accuracy.
E. Modelling Steps
1. Draw the layout sketch
We only need to use a few of the provided dimensions to fully define the shape of the layout. Rename the sketch "Layout Sketch"
Notice that I'm making the highlit dimension larger than on the sketch. That is done to provide material for trimming. The original drawing finishes the frame where the crosspiece (second from the bottom) hits the right frame. (see below for details)
2. Create a weldment and draw the first C channel piece
By creating your first structural member with Insert>Weldment>Structural Member you add a weldment feature to the part. Pick the first line from your sketch, then pick your weldment profile from ansi inch. Notice that by default we neither have a 4x7.3 C channel or a 2.5x2x0.25 angle.
We need to backup first and create our own weldment profiles.
3. Build your own structural profiles
SolidWorks stores the default weldment profiles in
(installation)>data>weldment profiles. You should create your own weldment
profiles outside the installation directory. Create a new directory
elsewhere. You need to create a directory hierachy as follows:
Standard
Type
Section
In our case you set up
steel sections
C Channel
L Angle
Copy one of the default C channels (4 x 5.4.sldlfp) file into your new "C channel" directory, and copy one of the default L channels (2 x 2 x 0.125.sldlfp) file into your new "L channel" directory. Rename them to your final dimensions (C4 x 7.25.sldlfp and L2.5 x 2 x 0.125.sldlfp).
In SolidWorks open the part as a Lib Feat Part, and navigate to your directory. You will open a part that contains a single sketch. Edit the sketch to your new dimensions (i.e. change the 1.584 in width to 1.721 in for the heavier C channel), then save. Repeat for the L angle.
Finally point Solidworks to your new directory via Tools>options>System>File Locations, then Weldment Profiles. Add the new directory for it to show up in the drop down list.
4. Add your first C channel
Go back to step 2 and Insert>Weldment>Structural Member. Watch the orientation of the part.
Also, because the L channels and C channels aren't the same height, but are probably at the same "top", select the Locate Profile button to pick a top corner of the profile to lie on your sketch plane, not the default center of the profile.
5. Complete your C channel assembly
At this point none of the members are trimmed. Just extrude them all along the sketch lines.
6. Complete your L angle pieces
Pick the other structural section and complete your frame assembly.
7. Trim the frame pieces to size
Use Insert>Weldment>Trim/Extend. For the corners where you're trimming and extending two pieces against each other, use an "End Miter". For the faces where you are trimming one piece against another body or face, pick and "End Trim".trim pick an end miter. For thePick the other structural section and complete your frame assembly.
8. Trim the length to the end position
In step 1 we extended the length of the railing beyond what's in the drawing for trimming. In the drawing it looks as if the frame stops where the cross piece (second from bottom) hits the right side.
Create a plane, parallel to front, going to the point of maximum extend on that cross piece. Select both right and left frame pieces, then use that plane with "Cut with Surface" to trim the two sides to their exact length. Be careful that you pick the right side to cut. Also, make sure that both pieces extend beyond the plane (which is why we extended the sides in step 1).
F. Communication
It is good practice to rename your features to help you understand - later on - how this was constructed and how it could be modified. Here is my resulting feature manager. Notice that this is a multibody part, but still a single part. There is only one file.
At this point we're all done. Let's use the information of the solid model to show some advantages over just having the 2d drawing above.
Option 1: Measure the Weight of the assembly - Assign a material
(plain carbon steel) and measure the weight with Tools>Mass Properties.
The
weight ofthis structure is 220 lbs.
Option 2: Determine the self deflection - Use Insert>Feature>Combine to glue all the pieces together (ignore any "welds" for now). Bring the part into CosmosWorksXPress, fix the two faces at the top, and apply a nominal 1N load at the bottom two faces.
Using the default values results in a 60,000 node model. You can display the deformed model.
Option 3: Check the dimensions - The initial drawing had several additional dimensions. Double-check those dimensions against the final model. The easiest way to show the dimensions would be to create a blank sketch on the top plane and add several driven dimensions.
Comparing those to the original sketch (I haven't figured out yet how to display driven dimensions in "nearest fraction."
7' 3 11/16" = 87.60 measured at 87.35"
4" = 4.00" measured at 3.84"
2' 5 3/8" = 29.38" measured at 29.28"
2' 7 1/16" = 31.06" measured at 30.84"
8' 5 7/8" = 101.88" measured at 101.79"
2' 0 3/16" = 24.19" measured at 24.19"
2' 4 1/4" = 28.25" measured at 28.27"
2' 0 11/16" = 24.69" measured at 24.64"
8' 1 5/8" = 97.63" measured at 97.47"
41.17 deg measured at 41.07 deg
We're mostly within 1/8" which is probably good enough.
Option 4: Evaluate the pieces - You have a multibody part with individual components that can be displayed and dimensioned individually. Here is one of the crosspieces to check the trimming.
Total Time to Build: 1 hr