Blend and fillet

Hello, I cannot understand in any way, than Blend differs from Fillet?

I think so: Blend = G2 continuity, softer appearance.
Instead, Fillet = G1, continuity of tangency, a little less soft.

Visual explanation using Rhino here:

Another one using NX (with audio):

There is a fundamental difference beyond continuity.

Fillet produces an arc which has constant radius and is tangent to the curves it links. The curves to be linked are trimmed or extended as needed so that the arc with specified radius fits to the curves to be linked with tangent continuity.

Blend produces a spline curve which has variable curvature along it’s length. Position, tangency or curvature continuity can be selected for the two curves it links. The curves to be linked are not modified. The blend curve is adjusted so that it has the selected continuity at each end.

Note that the curve produced by Blend with tangency continuity specified at each end will be different than the results of Fillet. The result from Blend will have varying curvature, while the result from Fillet will have constant curvature because it is an arc.

All thanks!

However I haven’t specified that I am interested in Fillet and Blend for edges of objects. What features at these 2 tools?

Do you mean FilletEdge and FilletSrf, and BlendEdge and BlendSrf?

FilletEdge and FilletSrf creates a fillet surface which has arc cross-sections. It’s part of a “pipe” . The input surfaces are trimmed and/or extended as needed, and the fillet surface is tangential to the input surfaces (G1 continuity).

BlendEdge and BlendSrf creates a NURBS surface. The cross-sections are not arc. The input surfaces are not altered. The type of continuity with the input surfaces is selected in the commands.

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BlendEdge works like FilletEdge - except that the blend is G2 not G1 - the input surfaces are trimmed. BlendSrf does not trim input surfaces. The commands VariableFilletSrf, VariableBlendSrf and VariableChamferSrf will either trim or not, depending on the command line options.


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Correct, my mistake.