Why Do We Have 3D Standards and What Is Best Practice?

When CAD meant 2D AutoCAD, and CAD standards meant naming layers and assigning line thicknesses, the job of the CAD Admin—or more likely, the drafting manager—was a lot simpler.

Even more advanced topics around 2D CAD Admin, such as part numbering systems, revision control and storage techniques, have for decades served as fodder for heated debates with neither side backing down. We have all seen or been a part of these arguments.

Maybe these days we have a lot more going on and we don’t sweat the details as much, or maybe we have simply acquired the wisdom over the past decades to settle the arguments. Either way, it is the role of the CAD Admin to simplify the requirements and make design documentation easy to produce, follow, access and interpret.

Skeleton method, also called Layout Sketch drives 3D assemblies from 2D sketches and planes.

CAD Standards

3D CAD has now been around for several decades. Many companies have grappled with evolving CAD standards to include ideas such as referenced documents, metadata, design and assembly techniques and other technical details involved in making the tools work for our processes.

Every company should go through the process of writing a CAD Standards and Best Practice document for their users. Working through all levels of the product development process helps you understand them more thoroughly and understand how your organization’s process fits in to the scheme. The concepts developed during standard writing can be extended far beyond just CAD or engineering technology. Modern CAD admin is not just concerned with drawings.

It is tempting to take a simpler approach, but you should look at the entire CAD process. For some, drawings may be the most important output of the process, even if they are at the end. There are other processes to consider, some of which use the CAD data or a portion of it. All of the data you produce along the way is reusable and it all potentially has value for multiple groups down the road.

Because of this, you have to regulate how you make all the data, not just the 2D drawing. We won’t tell you how to make standards for 2D drawings; after decades of hashing through this, there should be a consensus. You can Google to find it. What is missing is how and why to make standards and best practice guidelines for your 3D data.

Standards for 3D data—what does that mean? What do standards for 3D data control? Do you become the feature police? The fully-defined sketch police?  To an extent, yes, but there are automated tools to help you deal with that level of detail. The main job of writing 3D standards is to create and infuse a CAD philosophy into your organization. How do you control high level concepts in CAD? Much of how you write documentation depends on your primary CAD tool. For example, Onshape requires very different management ideas than SOLIDWORKS and standards that document your CAD process need to reflect the difference.

Twenty years ago, there were no guidelines on how to do parametric history-based CAD. Like anything never done before, you need to work backwards, starting from the result you want to see and then figure out how to get there.

This will prevent users seeing a crazy idea on YouTube or at the last online user group meeting and deciding that they would show how smart they are by implementing it during the company’s new product design.

Settings for PDM driven document management, revision control and libraries should be a documented part of your best practice documentation.

Best Practices

Best practices for 3D CAD can be loosely defined as:

  • Having no rigid rules. 
  • Being different from CAD standards.
  • Flexible suggestions to help prioritize options while keeping you from creating data that can’t be edited.
  • Intended to help your company use the software as it is intended to be used.
  • Allow some latitude for situations that require improvising.

When writing CAD standards, one approach is to treat all the data as if it is going into a PDM database. (Though if it is not going into a PDM database, it should be.) The first line of any CAD standard should be to specify which PDM product is being used. It should move through part numbering, revision control, attached metadata, additional embedded data and so on. You can include everything from service documentation to sales projections and actual results.

In real life application, CAD users at a company need to be using the same or similar processes—or to share a single CAD philosophy, if you will. What tools and techniques are used to reference a common layout for a large assembly? What references between parts do you use to position parts in an assembly? What level of analysis or simulation is required?

Best practice is a concept that is widely misunderstood, and not just in CAD circles. In particular, I have seen best practices imposed on a group by a manager who had no idea about technical content. They had found a list of “best practice” rules and imposed them without modification, without consideration and without knowing why. This leads to undue restriction, causing problems where none need exist, and a lot of strife and unnatural solutions. Don’t be that person. Best practice should make things easier, not harder.

The Difference Between Standards and Best Practice

Best practice is a set of soft guidelines that you need to employ right from the beginning, while standards are absolute requirements that generally start being employed after the best practice. Best practice guidelines keep you out of trouble, while standards help your organization look more professional. Best practices happen behind the scenes, while standards govern how you present yourself to people outside your department or company.

Standards for 3D Models

The reasons for creating CAD standards for 3D data are:

  • Establish goals for training.
  • Standardize design goals with other departments.
  • Make sure that your data can be used across multiple versions of the software.

One of the most important things a standard should do is to codify your training. Standards and training need to go hand in hand. You can’t expect someone to deliver a model in a certain format without making sure they understand that format.

When you get official software training from a reseller, remember that the reseller has to teach everyone from jewelry artists to mining equipment manufacturers. The person doing the training doesn’t necessarily know what the sales demo person knows about your company. Therefore, what they teach you is general.

To teach your users properly, your company needs to have someone do specialized training based on real models from your company and real processes developed for or by you. It might be best if your CAD Admin can work with a training specialist to develop and possibly deliver the training. If you have a lot of users (more than 10), you might consider doing the training in phases.

Design standards are also important when you have to work with other organizations or departments that have certain constraints. For example, injection molding design is very dependent on constraints in the injection mold process, which in turn depend on what kind of hardware is available or realistic for a given product budget. Design is cheap compared to recreating tooling.

Also, when you have to work with a machine shop, designing in such a way that requires the shop to buy and maintain a lot of specialized tooling may not be necessary. It may make sense to agree on a set of holes, a set of minimum inside radius cutters or quarter round cutters to avoid putting everything on a 5 axis machine with a 1/16” ball end cutter.

Here are some examples of standards used at real companies:

  • All brake-formed sheet metal parts must use the sheet metal tools in the software in the conventional way.
  • All plastic assemblies where complex shapes span multiple parts must use the master model technique as laid out in an appendix.
  • Plastic and cast parts should have the draft applied as separate features (not sketched or made as part of the extrude feature). Fillets should always come after draft in the feature tree. In cases that involve draft built into a complex shape, or where draft cannot be applied as a separate feature, use ruled surfaces to give a definite reference for the draft angle at the parting line.
  • Plastic parts should always be built using the input of the tooling engineer. The tooling engineer will bring any changes to your model for moldability back to you, so make sure you get their input first.
  • All mechanical actuator assemblies must be designed using the layout sketch functionality in SOLIDWORKS.
  • Components created by machining process are required to use the set of approved hole features and small inside radii established by the machine shop and laid out in an appendix. This is to simplify tooling expense and tool crib inventory.

Best Practices are Not Absolute

The first thing to learn about best practices is what “best” should describe. The temptation is to take the word literally, as in the pinnacle, the one singular solution to the exclusion of all others.

Do you measure your CAD models by rebuild time? Sometimes, in part, maybe. How about time to model? Again, maybe. Do you even evaluate your models in any way? That answer should be a qualified “yes.” Do you measure a part by the extent to which you have followed best practice?

The word “best” in this situation should be interpreted to mean an optimized balance between several competing goals. Best practices are not yardsticks to measure results, but guides line to help you achieve your goals.

Best practices are really a set of recommendations that help different people with different skill levels and experience to work together on a set of data in such a way that anyone can pick it up and understand what’s going on. Best practices help avoid problems. The more experienced your group, the less you need to enforce best practices. For every rule you can write, there is almost always a time to break that rule. An experienced user will know both the rule and when to break it. Inexperienced players really need the guidelines the most to help keep them out of trouble, especially the ones who know enough to be dangerous.

Best Practice is Not Universal

There is a reason why you cannot just look up a set of SOLIDWORKS best practices on the Internet. It’s because there is no single set that works for every company.

Best practices for a group of surface modelers will be different from a group of people who design parts that will be machined from a block of aluminum. Working with splines is intrinsically different from working with lines and arcs. Knowledge of the manufacturing process has a definite influence on best practice.

Is motion really necessary for your model? Do you need in-context relations, or does a master model approach work better for what you are doing? File naming, storage, and PDM. Do you use boundary or loft features? How do you name features? Do you use folders for features? Does everyone work under their own unique Windows login to make feature trails easily identifiable?

How to Write Best Practices

Write best practices for the purpose of avoiding problems. What kind of mistakes cost you the most time? With that under your belt, move on to more complex problems. By picking the low hanging fruit first, you will have more experience by the time you get to dealing with problems that are harder to identify and/or solve.

Where possible, document problems and solutions with actual examples from your data sets. Provide things such as templates, settings files, installation recommendations, network set up and most of all, give reasons why. A command to do something without justification may hinder its acceptance.

Avoid absolute language where you can. For example, try not to use words like “never” or “always” without qualification. There are very few things that you should ban entirely. For example, although it is usually a bad idea to leave errors in the model, sometimes you have to leave the model with an error state until you come back to work on it, or leave it for a more experienced user or until you have more information. Sometimes the software will not allow you to correct an error, or requires a creative method to delete the error without deleting a lot of other work. Be careful of how forcefully you say things.

Because you hired intelligent people and because you hired people you trust, make sure that they know you trust them. Where you have conflicting criteria, make sure your people know what the priorities of the business are. For example, if you have stated “fully dimensioned sketches are our #1 priority” and someone runs a macro that reads 1,000 points into a 3D sketch, can you still insist that fully dimensioned sketches are your #1 priority? Not really. Time is important and even more than that is the wise use of time. Dimensioning 1,000 points in 3D space would be a colossal waste of time. Instead, lock the sketch down and give it a name that warns people not to edit the sketch.

One of the things you need to keep in mind as you write the best practices document is how you intend to enforce it. Will your CAD Admin go through each drawing or model and approve it? Is it self-governing? Peer reviewed? Is there a best practice review as part of a drawing sign-off? Be aware that enforcing best practices may itself cost you some time. Of course, catching mistakes may save you some time.

Start With a Best Practice Template

There are a few pre-existing design philosophies that you may be able to borrow from. Some people have gone to great lengths to think out a set of rules or suggestions to help people make models that are more resilient to changes. Examples of these exist for horizontal modeling, resilient modeling and skeleton sketch techniques. These are fairly specific in their recommendations and mostly help you organize information. More general ideas would be things such as in-context modeling, master model techniques, layout sketches, multi-body methods and so on.

You can start by doing research and trying to understand some of these ideas and then combining the best of each to see what works for your company’s workflow.

Resilient Modeling System is a structured method for building editable assemblies.

Establishing Best Practice is a Technical Job

Make sure that if your best practices are written by a committee. The committee should employ your user with the best technical knowledge of the settings. If your best practice committee doesn’t know about the Freeze Bar or the Make Reference Sketch options, they might fall prey to recommend the deletion of all references and saving parts and assemblies as a Parasolid at the end of a project. That would be a huge waste of time and it kills the data design intent and re-usability.

It’s not a bad idea to have someone check your work. You might be able to run a draft of a best practice document by your reseller tech support organization. You might even consider hiring a consultant to help you find the best answers, or to settle disputes.


After it is all said and done, here’s what you can expect from a well-executed best practices document:

  • It should save you time rather than cost you time.
  • It is a set of suggestions or guidelines rather than strict rules.
  • It is flexible, as long as you know where to bend the rules.
  • It helps everyone in your organization work efficiently toward a common goal.

And remember, you can always borrow from pre-existing guidelines and don’t be afraid to call for help from those who have done it before.

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