When modifying the original value of the fillet in a sketch there are 2 different conditions that are causing constraint related failures.
1) 1) When there are 2 intersecting lines that are not in the horizontal or vertical position.
2) 2) When there is an intersection between entities that are not lines. (Arcs or Splines)
With the shown example I have locked the dimensions that I need to keep the sketch stable.
With case 1 even though the intersection is dimensionally locked when a fillet is applied it replaces these constraints.
Creo even recognizes the error it creates as shown below.
When you modify the fillet to the needed size it will invariably move the position as shown below.
With case 2 instead of having 2 lines I have replaced one of the lines with an arc. (The same type of results apply with using a spline), once again when I place a fillet it removes the original locked constraints. Once again in the message tree you see the “Dimensions to Endpoint Deleted” error. Additionally another troublesome entity is introduced. Notice that the system replaces out what should be a construction arc with a construction line.
When you modify the fillet to the needed size it will invariably move the position; see below.
With case 1 the work around is to replace the dimensional constraints with the original locked dimensions prior to modifying the radius value. This allows the constraints to work correctly, but it adds this extra step every time. If the locked dimensions truly were locked this would not be necessary.
With case 2 the work around is more complicated. The replacement of what should be a construction arc with a construction line means that I can’t just add X and Y locking dimensions to make constraints work correctly. The construction line tries to match up with a tangency on the arc and depending on the size of the fillet can really distort the results. In order to fix the constraints you have to extend the arc back to the original intersection (prior to the fillet), divide the arc at the place where the fillet intersects it, change the arc to a construction entity and then add the X and Y locking dimensions. If the locked dimensions were truly locked and if the construction entities at the intersection retained their original entity type (arc or spline) the work arounds would not be necessary.