Parametric drawing is a method of making geometries with the help of constraints or restrictions. AutoCAD introduced this feature back in 2010 and even after so many years of release the tool is still largely unknown or overlooked.
In this article, I have explained methods of using this feature with the help of a sample drawing. Let’s start by familiarizing with this tool.
All the tools related to this feature can be found on the parametric tab. The first panel of parametric tab is dedicated to Geometric constraints like horizontal, vertical, concentric and tangent. The second panel is for dimension related constraints like linear, aligned and radial dimensions.
Let’s take the example of the drawing shown below. This drawing has no defined center point for most of the arcs and to make this geometry parametric tools can be most efficiently used.
In this case, we will start this drawing by making the concentric circles of radius 5 and 8 at two different points. You can also make the line connecting the two concentric circles tangentially using the tangent option of object snap.
The final drawing after making these geometries will look like this.
The remaining part of the drawing can be made with the help of geometric and dimensional constraints of parametric tools.
To make the first arc on top of the top left circle select the three-point arc option and make an arc clicking at three random points in the drawing approximately taking the shape of an arc in the drawing. You don’t need to be specifically concerned about connecting the arcs tangentially or making them of any specific radius. Make the second and third arcs as well in a similar way with three-point arc tool. The final geometry should look similar to this one.
Now go to the Geometric panel and click on the Fix icon which looks like a Lock. Click on the circle of radius 8 units on the top left of geometry and then repeat the process for the circle on the bottom right circle having a radius of 8 units. You will notice that a lock icon will be placed close to both of the circles and their centers will have a red X sign indicating that their position is now locked.
Select Radius icon from the dimensional panel and click on circles on which Fix constraint are applied. You will notice that Rad1 and Rad2 constraints each of 8 units will be applied to both of the circles essentially restricting its radius from any change.
Apply the radius constraints to all of the arcs made in the drawing and change the value of radius to their respective values in the dimensional constraints as shown in the image below.
Once again move to the Geometric panel and select tangent constraint. Click on the circle of radius 8 units on the top left side of the geometry and then click near the left end of the arc of radius 21 units. You will notice that the arc will become tangential with the selected circle. Repeat the process with the arc of radius 12 units and circle of radius 8 units on lower right corner. Finally, apply tangent constraint between the arc of radius 36 and radius 21 and 12 units. The final geometry after applying these tangent constraints should look like this image shown below.
If you select any of the arcs and move them in the drawing area it will move in 2D space with all the constraints. In order to make drawing fully constraint select the arc of radius 12 units and move its center on the vertical line passing through the center of concentric circles on the lower left side of drawing area then apply fix constraint to the center of the arc. Similarly, move the center of the arc with radius 21 units on the horizontal line passing through the center of concentric circles on the top left of the drawing and apply fix constraint on the center of the arc.
Now the drawing is fully constraint and we can trim/extend extra geometries to clean up the arcs. The final drawing will look like this.
In this drawing, you will notice that there are many geometric as well as dimensional constraints that make drawing cluttered. In order to remove the constraints select Delete constraints option from Manage panel of the Parametric tab and select complete geometry and press enter.
The completed drawing will look like image 2 shown in the beginning of the article.
Applying Automatic constraints:
You can quickly apply automatic geometric constraints on any drawing. For applying the geometric constraints select the Auto Constrain option from the Geometric panel of Parametric tab then select complete drawing and press enter. The drawing will not become fully constraint as many dimensional constraints and also some geometric constraints will not be applied automatically and you have to manually add those constraints.
You can also keep infer constraints option ON to apply geometric constraints automatically to geometries on the go. To activate infer constraints select its icon from status bar or change the value of CONSTRAINTINFER system variable to 1.
When the Infer Constraint option is active the geometric constraints will be applied automatically to the drawing while creating it. In this case, also you can remove constraints by Delete Constraints option of Manage panel.
Do you also use these parametric tools in your drawings? Let us know in the comments below.
About the Author:
Jaiprakash Pandey is a Mechanical Engineer currently working as CAD Corporate trainer. He is an Autodesk AutoCAD certified professional and an Autodesk expert elite member. He provides training in AutoCAD, CATIA and other CAD products to corporate clients. He is a regular contributor to AUGI world magazine and he also develops AutoCAD video courses for Pluralsight and his own platform SourceCAD. You can reach his blog SourceCAD for more AutoCAD tips.
Parametric drawing is a technology that is used for designing with constraints, which are associations and restrictions applied to 2D geometry.
There are two general types of constraints:
- Geometric constraints control the relationships of objects with respect to each other
- Dimensional constraints control the distance, length, angle, and radius values of objects
The following illustration displays geometric and dimensional constraints using the default format and visibility.
A cursor badge displays when you move the cursor over an object that has constraints applied to it.
In the design phase of a project, constraints provide a way to enforce requirements when experimenting with different designs or when making changes. Changes made to objects can adjust other objects automatically, and restrict changes to distance and angle values.
With constraints, you can
- Maintain design specifications and requirements by constraining the geometry within a drawing
- Apply multiple geometric constraints to objects instantly
- Include formulas and equations within dimensional constraints
- Make design changes quickly by changing the value of a variable
Best practice: It is recommended that you first apply geometric constraints to determine the shape of a design, and then apply dimensional constraints to determine the size of objects in a design.
Designing with Constraints
When you work with constraints, a drawing will be in one of three states:
- Unconstrained. No constraints are applied to any geometry.
- Underconstrained. Some constraints are applied to the geometry.
- Fully constrained. All relevant geometric and dimensional constraints are applied to the geometry. A fully constrained set of objects also needs to include at least one Fix constraint to lock the location of the geometry.
Thus, there are two general methods for designing with constraints:
- You can work in an underconstrained drawing and make changes as you go, using a combination of editing commands, grips, and adding or changing constraints.
- You can create and fully constrain a drawing first, and then control the design exclusively by relaxing and replacing geometric constraints, and changing the values in dimensional constraints.
The method that you choose depends on your design practices and the requirements of your discipline.
Note: The program prevents you from applying any constraints that result in an overconstrained condition.
Use Constraints with Blocks and Xrefs
You can apply constraints between
- An object in the drawing and an object within a block reference
- An object within a block reference and an object within a different block reference (not between objects within the same block reference)
- The insertion point of an xref and an object or a block, but not to any objects within xrefs
When you apply constraints to block references, the objects contained within the block are automatically available for selection. You do not need to press for subobject selection. Adding constraints to a block reference can cause it to move or rotate as a result.
Note: Applying constraints to dynamic blocks suppresses the display of their dynamic grips. You can still change the values in a dynamic block using the Properties palette, but to redisplay the dynamic grips, the constraints must first be removed from the dynamic block.
Constraints can be used in block definitions, resulting in dynamic blocks. You can control the size and shape of dynamic blocks directly from within the drawing. For more information, see Add Constraints to Dynamic Blocks.
Remove or Relax Constraints
There are two ways to cancel the effects of constraints when you need to make design changes:
- Delete the constraints individually and later apply new constraints. While the cursor hovers over a geometric constraint icon, you can use the Delete key or the shortcut menu to delete the constraint.
- Relax the constraints temporarily on selected objects to make the changes. With a grip selected or when you specify options during an editing command, tap the key to alternate between relaxing constraints and maintaining constraints.
Relaxed constraints are not maintained during editing. Constraints are restored automatically if possible when the editing process is complete. Constraints that are no longer valid are removed.
Note: The DELCONSTRAINT command deletes all geometric and dimensional constraints from selected objects.
The parametric drawing is a method of making geometries with geometrical or dimensional constraints or restrictions. These constraints are applied to the geometry with respect to certain references or other geometries. Parametric drawings update itself if any one parameter is changed, this also helps in maintaining design intent.
This feature of parametric drawing was introduced in 2010 version of AutoCAD. This article explains the concepts of Parametric Drawing, Constraints and Formulas in AutoCAD. Let’s start with applying constraints in the drawing with the help of a simple drawing.
Make a rectangle with any dimensions and a circle at the geometric center of the rectangle. Now go to the Parametric tab and select the linear option from the Dimensional panel. Click at the top left vertex of the rectangle and then click at the top right vertex and place the linear constraint. Similarly, apply the linear constraint on any one vertical side of the rectangle.
Linear constraint on Dimensional panel
The dimensional constraint is different from the simple dimensioning and should not be confused with that. Select Diameter constraint from Dimensional panel and apply it to the circle at the geometric center of the rectangle. Now apply the linear constraint to the circle with respect to the horizontal and verticle side of the rectangle.
Now select Fix constraint from the Geometric panel and click at two diagonally opposite vertices of the rectangle to make it fixed. Now select Perpendicular constraint and apply it on three vertices of the rectangle. The geometry is now fully constrained as shown in the image below.
Making simple formulas:
Let’s assume that we want the geometry made above to behave in such a way that diameter of the circle always remains half of length of the rectangle. For that, we can create a simple relation or formula and apply it to the respective geometries in the drawing.
Click on Parameters Manager icon on Manage panel of Parameters tab or use its command equivalent PARAMETERS. Click on the icon on Parameters Manager palette, a new list User Parameters will be added to the palette.
Parameters manager palette
Double click on the user1 parameter and change its name to DIA. Double click again on expression column next to DIA and type d1/2 which mean DIA parameter will be equal to d1/2 where d1 is the length of the Rectangle.
You can now use this formula to define the diameter of the circle, double click on Expression column of dia1 row in parameters manager palette and change it to DIA as shown in the image above, the circle will update according to changed dimension and diameter of circle will become equal to value of DIA which is half of length of rectangle.
To test this formula go to d1 in drawing area and change its value, you will notice that diameter of the circle will also change accordingly not only in parameters manager palette but also in the drawing area.
Making nested formulas:
In the above example, I have used a simple formula but you can also use nested and complex formulas that involve the use of sine, cosine and logarithmic expressions. I will use the same example of rectangle and circle to explain this as well.
Suppose we want to change the length of the rectangle (d1) in such a way that it always remains five units less than twice of the width of the Rectangle (d2) then we can use this expression (d2*2)-5 to define the length of the rectangle where d2 is the width of the Rectangle.
To apply this formula click on the icon and double click on user2 and rename it to EXP. Again double click on the expression box next to EXP and write the expression (d2*2)-5.
Now write EXP in d1 row expression column as shown in the image below. You will notice that length of rectangle changes to reflect dimension according to formula. Final settings in parameters manager will look like this.
The final parameters in Parameters manager palette
You can test this nested expression by changing the value of d2 which will change dimensions of all dependent geometries including the diameter of the circle.
Do you have questions related to this tip? Let me know in comments below.
I am a mechanical engineer and I have worked with Design, Manufacturing and Training industries but now SourceCAD is my full-time work and I use it to train students all over the world. I also train corporate clients and help them develop the skill set of their workforce. I am Autodesk AutoCAD Certified Professional and an Autodesk expert elite member. I am a regular contributor of AUGI World magazine and apart from SourceCAD I also develop AutoCAD video courses for Pluralsight and other E-Learning businesses.
Parametric design tools aren’t just for programs like Inventor software, Revit software, or AutoCAD Civil 3D software. There is also a set of parametric drawing tools that you can use to create dynamic relationships and constraints between objects in AutoCAD software. The parametric drawing tools will revolutionize the way that you draw and edit objects in AutoCAD software. This class will introduce you to parametric drawing in AutoCAD software by using both geometric and dimensional constraints to add intelligence to your objects. You will learn how using Auto Constrain and Inferred Constraints can help you quickly add constraints and change your process from drafting to modeling. If you’ve ever wanted geometry in your drawing to update based on changes that you’ve made to other objects, or if you’ve wanted to type a new value into a dimension and have the object update based on this new value, this class is for you. This session features AutoCAD. AIA Approved
- Learn how to create geometric relationships between objects by adding constraints
- Understand dimensional constraints
- Learn how to identify and edit constrained objects
- Learn how to use inferred constraints to have AutoCAD automatically define constraints for you
.Parametric drawing AutoCAD 2022
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