What is a ʼParametric Blockʼ in BricsCAD?
Short Answer
A parametric block in BricsCAD is a block definition that uses geometric and dimensional constraints so its shape can change predictably when edited. The most common professional method is creating or editing the block, then applying constraints with BMCONSTRAINT. Limitation: not every legacy block is clean enough to constrain reliably.
What You Need to Know Before
Warning: If the block geometry has gaps, overlapping entities, or poorly defined base geometry, constraints can over-constrain the block or make it fail during edits. Dynamic behavior also depends on how cleanly the block was built before constraints are added.
How to Create a Parametric Block
Command: BMCONSTRAINT
Shortcut: No default shortcut in many workspaces
Quick Steps:
- Open the block in the block editor, or create a block first from the Ribbon using the Block panel, then enter block editing.
- Run BMCONSTRAINT and apply geometric or dimensional constraints to the block geometry; use the needed constraint type and keep critical relationships locked.
- Test the result by changing a dimensional constraint value in the Mechanical Browser or Properties panel, then save and close the block.
Variables & Settings
Key Setting: Constraint type and dimensional value
Expert Setting: Use geometric constraints first, then add dimensional constraints only where controlled change is required. This reduces over-constraint errors and keeps the block easier to edit.
Why it Fails
- Cause 1 (Geometry): Lines, arcs, or profiles are not fully connected or contain duplicate entities, so constraints solve unpredictably.
- Cause 2 (layers/Locks): Geometry inside the block is on locked layers, preventing edits or constraint changes.
- Cause 3 (Command/Logic): Too many constraints are applied, creating an over-constrained definition that cannot solve cleanly.
Quick Fix & Best Practice
- Quick Fix: Open the block, clean the geometry, then rerun BMCONSTRAINT with fewer dimensional constraints and only essential geometric relationships.
- Manager’s Verdict: Use parametric blocks when you need controlled part variations in repeated design work. Avoid them for messy imported blocks or simple symbols that do not need adjustable behavior.
FAQ
Can a regular block be turned into a parametric block?
Yes, if you edit the block and add valid constraints to its geometry.
Are parametric blocks the same as dynamic blocks?
No, BricsCAD parametric blocks rely on constraints, while dynamic blocks are an AutoCAD-specific feature set.
Can I edit a parametric block after insertion?
Yes, if the constraints were built correctly, you can change the controlled dimensions and behavior.
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