Gerald Davis
Ann Arbor
Amateur sociologist, Detroit patriot, smug vegetarian. Org theory, social movements, corporate power, finding alternatives. Opinions generated at random.
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Articles by Gerald Davis
Workflow for modeling an involute spur gear
FIGURE 1. At a glance, these gears appear to be the same. One of them has the correct involute face curve on its teeth. The other two were easy to make, just not useful for manufacturing. Editor’s Note: Supporting CAD files for this column can be found here. Acknowledgement: Thanks to reader David Guza for suggesting this gear-headed article. Gear models come from three primary sources—download, wizard, or DIY. Figure 1 shows an example of the same gear from each of those sources.
A review of CAD workflow for tackling what-ifs
FIGURE 1. An image for a floor plan is used to create a virtual prototype of the garage. The image is inserted as a Sketch Picture into the sketch for the 3D model. The Sketch Picture is scaled one-to-one to be a useful reference. Editor’s Note: Supporting CAD files for this column can be found here. Mainstream 3D CAD is useful for visualizing what-ifs. A home improvement project is full of what-ifs and is useful here for exploring a few CAD tricks.
A review of workflow for revising a CAD model
FIGURE 1. A stop switch is to be added to the battery cover on the drone cart. The workflow to add the needed cutout while maintaining the proper bill of materials for the cart and cover imposes a bit of discipline. Editor’s Note: Supporting CAD files for this column are available on request. Figure 1 presents a routine CAD task: add a component to an existing assembly. In this example, the battery cover needs to gain a cutout for mounting a stop switch.
A quick overview of three CAD modeling techniques
FIGURE 1. A sketch of the cross section of a revolved body might show a best way to model the part. All of the information is contained in a single sketch. However, the history of the design’s evolution is not evident. Editor’s Note: Supporting CAD files for this column are available for download here. Mainstream 3D CAD offers many alternative modeling techniques that can be combined to arrive at about the same ending point.
Modeling threads in 3D CAD
FIGURE 1. The thread in this bottle cap has lead-in and lead-out to help avoid cross threading and improve sanitation. The thread is modeled as a sweep of a profile along a helical curve. The helix varies diameter to fade the lead-in and lead-out. Editor’s Note: Supporting CAD files for this column are available for download here. Figure 1 shows a threaded bottle cap. The start of the thread (the thread lead-in) has zero height; the thread’s projection grows deeper as the thread spirals.
Mind the gap when modeling interlocking features
FIGURE 1. Interlocking fingers allow two panels to be joined with a friction fit. A sketch can be used in different ways to model the trapezoidal tabs. Editor’s Note: Supporting CAD files for this column are available for download. In the process of modeling the interlocking fingers in Figure 1, a variety of CAD tools were used, including Make Block, Sketch Pattern, and Split. To create a gap for fabrication tolerance, we will compare the merits of using a Cut-Extrude rather than a Face-Move.
A conversation about sketches in 3D modeling
FIGURE 1. Here’s the plan for the generation of a 3D STEP file from a 2D sketch. For this demonstration, a centerline sketch controls the shape of a 3D model. How that model is chopped (or not) controls what will be in the STEP file. Editor’s Note: The inspiration for this column comes from a YouTuber who caught Gerald Davis’ eye. In one episode, he fabricates a Mandalorian helmet. Those familiar with the Star Wars universe know that Boba Fett of “The Empire Strikes Back” fame is a Mandalorian.
Creating slots and tabs in 3D CAD the easy way
FIGURE 1. A gusset can be located in a bracket with tabs and slots. One could model those features as cuts and extrudes with the controls built into the sketches, or one could use the Tab and Slot tool for much more versatile control. Editor’s Note: Supporting CAD files and graphics for this column are available for download. A pattern of tabs and slots can be created with controls for quantity, size, shape, and various offsets for location and tolerance.
Creating bend notches the easy way
FIGURE 1. CAD makes it easy to model sheet metal. Just a simple 2D line sketch (upper screen shot) can control radii and thickness that will accurately unfold (lower screen shot). Some standards may apply. Editor’s Note: Files associated with this column, one of which is a sample part that uses a gauge table that was once used for sheet metal production, can be downloaded here. The incorporation of sheet metal in a product presents numerous design-for-manufacturing opportunities.
Working with flat patterns of coined corners
FIGURE 1A. The Swept Flange requires a sketch for the profile and edges to select for the path of the sweep. The resulting flange can be unfolded. The previous episode presented a CAD technique that allows coined sheet metal corners to seem to be unfolded. For demonstration, leather was the target material instead of sheet metal. Although effective, the tip was more of a trick than a practical workflow.
Sheet metal CAD skills applied to leather
FIGURE 1C. A 3D CAD model gives a reasonable visual prediction of what the leather might look like in the final dopp kit. Note that the 5-mm perforation pattern enters and exits the bend with equal spacing. Mainstream 3D CAD is great for sheet metal projects. It’s a tool with which to make well-behaved sheet metal models that are both visually and mechanically accurate—useful for generating flat patterns and other predictions of the sheet metal changing shape under the influence of tooling.
With changes in CAD hierarchy, don’t forget the pointers
Designs change. As a result, revisions to documentation are required. When the design change involves the hierarchy of files in the CAD database—that is to say, which is the parent of what—a few pointers come to mind. To illustrate what the CAD workflow can involve, we present the assembly shown in Figure 1A. Our tank lid assembly features a sheet metal lid, which is a subassembly.
Design for function before design for manufacturability
The CAD model shown in Figure 1 is an example of a design for mounting components in an electronic assembly. An exploded view is shown to the left of the completed assembly. This project is offered for review of the confluence between design for function (DFF) and design for manufacturability (DFM). The lower sheet metal bracket has four captive threaded spacers. A critical design goal is to have their location match the mounting holes in the printed circuit board (an SD card reader).
Finding efficiencies when modeling weldments
The evolution of a two-sheet drawing is shown in a before-and-after format in Figure 1. Please don’t strain your eyesight. The details on these example drawings are offered to give an impression of how mainstream 3D CAD contributes to revising a typical 2D drawing. This is pretty close to a real-world project. The drawing in Figure 1 specifies the welding requirements and the final overall size of the completed stand.
A review of tricks to pose downloaded models for review
Editor’s Note: CAD files associated with this column can be downloaded here . In Figure 1, the door to an enclosure is positioned to indicate the range of door motion and access available for service. A glance is enough to get an understanding of the mechanism. In this (imaginary) project, screwdriver access is limited to the terminal blocks, which must be tightened before being snapped onto the switch actuator. But there might be alternatives.
A review of tricks to reduce rebuild time in CAD modeling
In the CAD brand used here, rebuild time is the patience that it takes to wait out the update of the database that is maintained by the Parasolid kernel (the geometric modeling engine, within 3D modeling applications). This rebuilding can be triggered by initial loading, by edits to a chain of parametric links, or by changing the shape of a body. Even with fast computers, some complex models can take hours to rebuild. In general, less rebuild time is desirable.
The many useful results CAD can deliver
Editor’s Note: CAD files associated with this column can be downloaded here. Figure 1 presents a screenshot of a fabrication drawing. Such 2D drawings are often one of the deliverables (aka useful results) from CAD effort. As part of a quality control program, part number and revision control of specification help to minimize random outcomes. Most importantly, the revision control/document control process assures that improvements are implemented without surprise.
A consistent workflow for modeling wires can save time
Editor’s Note: CAD files associated with this column can be downloaded here. Figure 1 presents a switch with wires posing as a CAD model. Most of the components were downloaded from an online hardware store. The wires are the task at hand. They need to be modeled as individual parts. This brand of CAD software offers an add-in to make the routing and modeling of such path-driven objects more menu-driven and controllable.
Linear versus sketched patterns for real-time demonstration
Editor’s Note: CAD files associated with this column can be downloaded here. Let’s discuss a project that required revision of an existing virtual prototype. The mission was to rearrange the components. The task required importing a STEP assembly (see Figure 1). Recreating the product manufacturing information and the 2D drawings was expected to be the most time-consuming part of the project, which included preparing the model for a real-time design and review meeting.
The use of sweeps and twists in 3D CAD
Editor’s Note: CAD files associated with this column can be downloaded here. Figure 1A shows a sketched profile. The dimensions and shape are arbitrary. It is simply an example of a routine 2D sketch in 3D CAD. Figure 1B shows that same sketch being used to create a solid body. In this example, the body is 1 in. tall. This could have been accomplished using a Base-Extrude, but in Figure 1B the solid body is created as a sweep along a path.
Analysis can help when working with sheet metal
The sheet metal bracket shown in Figure 1 has been the topic of discussion in the past couple of columns. In particular, we’ve considered modeling the project as either a multibody or an assembly, as well as the nuances of modeling for manufacturing. Efficient CAD practices add merit, but all that really matters is the suitability of the design.
What a review of a CAD model says about its creator
This is a review of the CAD techniques used in the sheet metal project shown in Figure 1. The product is functionally a three-sided socket (0.090-in.-thick 5052-H32 aluminum), featuring captive studs. The bracket is to be 4 in. by 2 in. by 2 in. on the inside and mounted with three ¼-20- by 5/8-in.-long studs. With not much more information than that, the project is imagined as part of a job application for a position as a CAD jockey. Many tools are available in CAD.
How to deliver a step-by-step process overview in CAD
Editor’s Note: CAD files associated with this column can be downloaded here. A recent entry in the engineering change order (ECO) log simply stated, “Remove the bracket from inside the box.” I was puzzled by this change. The bracket is essential to the design. The box is a functional accessory. Before arguing with the reviewer, let me show you my investment in this project thus far. Sheet metal origami is a mixed blessing.
Just how much detail is needed in a 3D model?
Editor’s Note: CAD files associated with this column can be downloaded here. In the real-world experience of CAD, a useful 3D model often lacks perfect accuracy. Not all details need to be fully specified, and some details don’t need to be modeled. As an example of acceptable deviation from reality, the starting angle of the spiral in a tapped hole is likely to be randomly created during a machining process.
Managing configurations in CAD without using a design table
Editor’s Note: CAD files associated with this column can be downloaded here. One of my favorite tricks while showing off at CAD user group meetings is the “Rebuild All Configurations” button. Rebuilding has special meaning in CAD. It is the software’s process of calculating where the 3D surfaces should be, based on the constraining 2D sketches. Rebuilding is time-consuming, so the software can be told to rebuild only when commanded. Sometimes this approach gives incomplete results.
Design tips for transitioning duct work from square to round
Editor’s Note: CAD files associated with this column can be downloaded here. We start at the end with a sheet metal project as presented in Figure 1A. The purpose of this bit of transition is to duct from square, approximately 36 in., to round, approximately 12 in., in the span of about 18 in. This funnel is to be stout. It will be banged about by things as big as baseballs. The material and finish are proven (borrowed from related equipment). It will be 14-ga.
Tips for planning a product development project
Editor’s Note: CAD files associated with this column can be downloaded here. The 3D CAD model shown in Figure 1A first appeared in a February 2008 column. It is useful as an item that is not likely to conflict with any existing trademarks or patents, but could. The focus at the time was on design for manufacturing (DFM)—specifically, sheet metal fabrication. There are several rules of thumb that are badly bent by this model. A few improvements are shown in Figure 1B.
Tips for DFM, workstation setup, and various other best practices
Editor’s Note: CAD files associated with this column can be downloaded here. Figure 1 is a screenshot from a mainstream 3D CAD workstation. It is set up with the Feature Manager on the left, the flyout Property Tap on the right, and the Graphics window in the middle. The two component parts in this assembly are displayed with their descriptions visible in the Feature Manager. Some workstations display many data fields in the Feature Manager by default. This can be distracting and unhelpful.
Can Strategy Address the Climate Crisis Without Losing its Essence?
How should academic fields take on the existential risks created by the climate crisis? What are the moral obligations of business schools at a time when the operations of business are the greatest hazards to our planet? Just 20 companies are responsible for one-third of the world's carbon dioxide emissions over the past half-century.[1] Without rapid decarbonization of business over the next few years, there is little hope for a habitable planet.
Tips for creating sheet metal tubes with perforations
Editor’s Note: CAD files associated with this column can be downloaded here. Exploded Views and their various methods and merits were discussed in the previous episode. In this column, the conversation continues. Figure 1A presents a 2D drawing using an Exploded View and a corresponding bill of materials (BOM) table. A drawing might include balloons to tie rows in the BOM table to identified components in the Exploded View. The Exploded View is stored in the 3D model’s file.
Creating Exploded Views quickly
Easily access valuable industry resources now with full access to the digital edition of The Fabricator. View the Digital Edition Easily access valuable industry resources now with full access to the digital edition of The Welder. View the Digital Edition Easily access valuable industry resources now with full access to the digital edition of The Tube and Pipe Journal.
Tips for creating a kinematic model
Editor’s Note: Download files associated with this column here. The CAD task at hand in this episode is to model a hinged door featuring a magnetic touch latch. A preview is shown in Figure 1.
Tips for efficient sketching in 3D modeling
I recently was asked what I do. As the guy running the CAD system, my job is to document the daydreams. I am a doodling stenographer. Instead of using shorthand, I sketch. My most successful CAD projects have targeted fabrication (as opposed to something only for virtual reality). That observation is offered as a qualifier to the CAD wisdom offered here. I don’t sell software. I just use it. I have bias because of long exposure to a particular brand of mainstream 3D CAD.
Tips for tackling virtual sharp points and bend lines for oblique angles
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Tips for tackling virtual sharp points and bend lines for oblique angles
When it comes to 3D modeling, a CAD jockey usually has more than one way to solve a design puzzle in CAD. For example, the creation of a virtual sharp point located at the intersection of two lines is easy if you know how. In another example, bend lines on a sheet metal drawing can be addressed with a bit of manual intervention. Virtual Sharps and the Z Dimension Figure 1A presents a sheet metal bracket as it is being edited/reviewed in mainstream 3D CAD.
Tips for better illustrating component relationships in a 3D model
Exploded Views are useful for illustrating how components are related. To demonstrate the process of adding an Exploded View to an assembly and then adding Explode Steps to it, the assembly in Figure 1 will be used. Figure 1 shows our assembly after a new Exploded View is first added. An Explode Step is ready to be added. Figure 2 shows the setup for the first Explode Step. Here’s a CAD tip: Select various related items so they reposition as a group. In later steps, separate the parts in that group.
Coordinating CAD techniques with planning documents leads to user-friendly models
One of the joys of mainstream 3D CAD is the ability to control what changes and what remains the same as the model evolves. As an example, holes for fasteners can maintain desired alignment while other features change around them. Set-and-forget linkage allows you to do it right, do it once, and move onto the next thing. There are more than a few methods of creating links. This discussion contrasts assemblies with multibody or derived parts.
Sustaining engineering with the use of logs, tables, and a hierarchy of CAD files
What follows is a description of CAD activities involved in revising an existing drawing, one that is usually distributed as a PDF and maintained as a SLDDRW. As a disclaimer, the brand of CAD and, most importantly, my drafting standards are specific to this demo. As examples of procedure and methods that are “as you like it,” I use logs (spreadsheets) here to issue part numbers and to serialize engineering change orders, as well as tables to document revision levels and required components.
Finding the CAD technique that gets the job done
Figure 1A shows a motorized cart base. This imaginary shop cart was introduced as a CAD project in the August 2021 episode. A few revisions to the motor’s mounting have been introduced as the design has evolved. Figure 1B shows an updated model for the frame. The best way to model such a frame seems always to have been the other way. The grass is greener on the other side of the mouse, as it were. Using our brand of mainstream 3D CAD, a few of the other ways to model it could be: As a multibody part.
How CAD technique adapts to the requirements for product documentation
A problem has been reported and redlined on an assembly drawing as shown in Figure 1A. The problem is that the exploded view of the assembly is incorrect. The illustration does not show that a cover must be removed to gain access to the set screw in the fan wheel for connection to the motor’s shaft. A revised drawing is presented in Figure 1B. The cover and fan blade, with its set screw, have a more informative orientation. The reviewers approve that revision. “But, while you’re at it,” they say.
How some CAD tools deliver automatic design for manufacturability results
In the late 1970s, I was paid to play with G-code canned cycles, fixed programming instructions that help CNC equipment perform repetitive operations. The length of the paper tape was one measure of the program quality. In addition to standard canned pecking cycles, CNCs featured (and still do feature) brand-specific G-codes for bolt hole circles, lines of holes, and curved patterns of all kinds.
Using a Design Table in 3D CAD to produce varied models
Reader Joshua Raimond of Denver wrote to ask about a filter in CAD that was covered in a June 2016 column. The question: How is its flat layout modeled? The item in question—a cupcake filter—is shown in Figure 1. There’s no magic here. The flat paper disk was created separately from the formed cup. The configurations determine which of two bodies to display—pleated or flat.
How to use imported CAD models
Imported CAD models often are preferable to detailed native CAD creations, particularly for commodity items that will be purchased rather than manufactured. Such “poser” models typically are used in three ways: to populate a bill of materials table, as actors in a virtual prototype, and as a starting point for a new design. Figure 1 shows an example of such a downloaded import. Here, a 3-in. hex standoff is the star of the show.
Review native CAD models to glean and gain modeling technique
When presenting and reviewing a design, props are often used to convey scale, operation, and feel. We introduced a tote box design using such props (hand tools) in August 2020 (see Figure 1). To avoid excess labor on the part of the CAD jockey, such visual actors are often downloaded from sources such as mcmaster.com, 3dcontentcentral.com, and grabcad.com. The author is familiar with these resources and values them greatly.
Tips for preparing a model for review
We are in the midst of using our lovely Custom Properties form to add information to the model preparation of the CAD project for scrutiny by others. As part of this effort, we are using a self-propelled shop cart to carry forward the discussion. At this stage, the 3D CAD is in its middle stage of development. Many details are emerging. The progress needs to be reviewed and priorities set for the next round of activity.
Tips for decals, zonal section views, and shading of drawings to be used in presentations
Happy New Year! With that said, the upper image in Figure 1 shows an annual change that is needed to the decal being used in an imaginary shop cart project. The overall view of the cart shows the decal’s location, and the close-up (to the right) shows the “©2022” that should now be “©2023.” With the brand of CAD being used here, decal has special meaning. It is a CAD feature—an image applied to one or more surfaces of a CAD model.
Tips for cloning product manufacturing information from one CAD file to another
CAD’s ability to fill in the title blocks on drawings relies upon File Properties to convey product manufacturing information (PMI) from the model to the drawing. Disclaimer: That statement is perhaps true only for a brand of mainstream 3D CAD and for the way in which its tools are being used in this demonstration. File Properties are a feature of the Windows operating system.
Tips for perfecting table templates
The creation of fabrication drawings usually involves tables, such as revision tables, bills of materials, and hole location tables. As mentioned in the discussion of template design in the September edition of this column, tables have anchor points to help with drag-and-drop location snapping. Tables have additional features that might be useful when designing and refining templates. For example, one particular setting forces uppercase display for all the entries in the table.
CAD workflow for creating drawings in batches or one-offs
Templates are useful when creating drawings for fabrication. An existing drawing could be used as a template—a starting point. Look at it as a clone, albeit with legacy data. Alternatively, starting with a Drawing Template is the equivalent of starting with a blank form. A conventional Drawing Template might have several other templates nested within it. Recent episodes of this column have discussed templates for a Sheet Format, a BOM table, revision table, title block, and general table.
THE Voice of the Independent Publishing Industry
Book Review : Biography/Journalism Algerian Diary: Frank Kearns & The "Impossible Assignment" For CBS News Gerald Davis' book provides a wealth of scattered pieces of the puzzle that made up the 1950’s French-Algerian War (or Non-War), as well as a look at the state of television journalism at that time, before, and beyond.
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