Extrude properly
New, add, remove, intersect — and the end conditions that keep an extrude correct when the part changes.
By the end you can
- Use all four extrude operations and say what each one is for
- Pick an end condition that survives a change to the part around it
- Extrude symmetrically to keep a part centred on its plane
On this page · 4 sections
Extrude is the feature you will use more than all the others combined. It is also the one most people use at about a third of its capability.
The four operations
- New
- Creates a separate part. Use it when the thing you are extruding is genuinely its own component.
- Add
- Fuses the material into an existing part. A boss standing off a plate is an add.
- Remove
- Cuts material away. Every pocket, slot, and lightening hole is a remove.
- Intersect
- Keeps only the volume shared with an existing part. Rare, but the cleanest way to trim a part to a complex envelope.
Watch what 'New' does to your parts list
Forgetting to switch from New to Add is how a studio ends up with fourteen parts that should have been three. The parts list on the right is the quickest way to notice.
End conditions are where models break
Blind — go a set distance. Simple, and wrong more often than you would think. A blind cut of 12 mm through a 12 mm plate is fine until someone makes the plate 14 mm.
Up to face / Up to part — go until you hit specific geometry. Now the cut adapts when the plate thickens.
Through all — go until there is nothing left to cut. For a bolt hole that must clear the whole stack, this is almost always what you want.
Symmetric — grow equally in both directions from the sketch plane.
Symmetric keeps the origin meaningful
If you sketched on a mid-plane to stay centred, extruding blind in one direction throws that away immediately. Symmetric keeps the part straddling the plane, which is what makes mirroring to the other side of the robot a single feature later.
The FTC version of this
A drivetrain plate has bolt holes that must clear whatever thickness the plate ends up being. Someone always changes plate thickness — from 3 mm to 4 mm after the first bend test, or from aluminium to polycarb for weight.
- Bolt holes: through all. They keep working at any thickness.
- A bearing pocket that must be exactly 3 mm deep regardless of plate thickness: blind, because the depth is the requirement.
- A slot that has to break through into an adjacent pocket: up to face, so it tracks the pocket if the pocket moves.
The question to ask each time is not "how deep is it" but "what actually determines this depth?"
Check yourself
You are cutting bolt clearance holes through a drivetrain side plate. The team is still arguing about whether the plate will be 3 mm or 4 mm aluminium. Which end condition should the cut use?
Next
Holes and fillets — two features with dedicated tools that most people fake with extrudes.
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