Fillet
Use Fillet to round an edge. Select one or more edges, press F, and type a radius.
One radius, many edges
A fillet feature carries a list of edges and a single radius. Every edge in it gets the same number. Two different radii on one part are two fillet features, and splitting them that way lets you change one without touching the other.
The radius accepts anything a dimension does: a number, a parameter, an expression. It has to be above zero and no more than 100 mm.
Every edge must belong to the same body. Select edges across two bodies and the feature refuses rather than guessing which one you meant. Pick again inside one body, and make a second fillet for the other.
Why fillets fail, and what to do
A fillet is the operation most likely to fail on a real part. The message names four causes without telling you which one you hit:
Fillet geometry failed — common causes: radius too large, edges interfere, edges not connectable, tangency problem. Try a smaller radius or fewer edges.
That list is in the right order. The usual cause is a radius bigger than the material around the edge. A 5 mm round on a 6 mm wall has nowhere to go. The second is two edges whose rounds would run into each other.
The practical route out is the one the message suggests: halve the radius and rebuild. If it works, the problem was size. If it still fails, split the feature. Round the edges that work in one fillet, and deal with the awkward one separately.
When an edge disappears
A fillet tracks the edges you picked rather than the spot where you clicked, so it keeps hold of them through most upstream edits. When an edge genuinely stops existing, the feature rounds the ones that are left and carries on. It does not warn you. The model quietly comes back with three rounded corners where you asked for four.
After any edit that changes the shape a fillet sits on, count the rounded edges and re-pick the ones that were dropped.
See also
- Chamfer: a flat bevel instead of a round
- Shell: hollowing a part after you have rounded it
- Working with Several Bodies: why order keeps fillets alive