Fillet Edge vs Blend Edge Radius Differences and Suggestion

I recently discovered in a relatively costly manner that the actual radius that results using curvature continuity under Solid - Blend Edges is something less (over the majority of the curve) than the radius entered as part of the command.

In my case, 1.00" was entered for the Blend edge command with curvature continuity ended up being about 0.75" across the middle of the curve.

I am not an engineer so this may be standard knowledge. However, unless it already exists, I am suggesting a command option within Blend Edges that has some control relative to what you would get if you filleted the edge or used tangential continuity. For example, if you select 1" than no part of the resulting edge will be less than a 1" radius.

Thank you.
Brian

You’re asking for something here which is difficult if not impossible to do. A blend edge starts out as a tangent (fillet) edge but is replaced by a curvature continuous one - the surfaces coming to that edge are trimmed back at the same location, then the surfaces are blended in curvature continuity instead of the fillet’s tangent.

IF it has to fit in the same spot, AND it has to have a radius no smaller than the fillet’s tangent radius, then it can’t have a radius any larger than the theoretical fillet radius either… therefore it’s just like a normal fillet. You can think about it this way - if you make the curvature less at some area on the blend, you have to make it sharper somewhere else to get the blend to meet the same edges.

So, in order to meet your conditions, the blend edge would have to cut more back from the original surfaces than a normal tangent fillet. This is certainly possible, but how much? There is no set answer, there are valid solutions for anything from “just a little more” to the the maximum that could fit on a given edge. So it ends up being something that’s pretty difficult to quantify.

–Mitch

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The use of the term “radius” in BlendEdge is misleading because it does not directly relate to the curvature of the blend surface. As Mitch discusses above a continuous curvature blend will generally have curvature which varies between the surfaces. The input “radius” is used to determine how far to cut back the surfaces from the edge using the same methods as FilletEdge, which only indirectly controls the curvature of the blend surface…

“Radius” is also misleading in BlendEdge because the radius of the resulting fillet is only guaranteed to have the input if the “rolling ball” method is selected. For the “distance from edge” and “distance between rails” methods the radus of the fillet will also depend on the shape of the surfaces and angle between them.

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Thank you for the explanation regarding how to approach “radius” in BlendEdge. That quantifies it in a way that I can work with.
Brian.