Same rail two sweeps yet mergeSrf says too far apart

Attached two sweep2rail surfaces, their junction is from a rail used for both sweeps.
As such the surfaces abutting there should be identical yet mergeSrf wont join the surfaces. I have this throughout the entire object made of rails all parallel as these are.

I also tried Join as well, fails.

Boolean Union works.

why the differences and is it ok with Boolean or wil some commands fail on it ?

separateSweepsSame rail wont mergesrf.3dm (116.9 KB)


The maximum gap between the adjoining edges is 0.149932 and you have the tolerance set to 0.01. (Gap between the edges can be found using CrvDeviation and selecting the edges.) Relax the global tolerance to 0.1 and Join will work. Relax the tolerance in MergeSrf to 0.2 and the surfaces will merge. Presumably BooleanUnion uses different tolerances.

You can also use JoinEdge which will pull the edges together and join the surfaces into a polysurface.

Possible reasons for the gap between the adjacent edges:

  • The edges of surfaces will not coincide exactly with the rails unless the ends of the swept sections are exactly on the rails.
  • Intermediate sections can result in the edge not coinciding directly with the rail, presumably due to difference in parameterization… It appears that the two surfaces you created using Sweep2 had different swept curve distributions.
  • Rebuild or Refit options used in Sweep2.

The surfaces have a better chance of merging if you use the surface edge as the cross-section curve for a sweep.

My suggestion: