Extra hidden geometry created on curved leg when mortise is created

I’m working on a cabinet on a stand with curved legs with rails and floating tenon joinery.
I use a separate tenon component and a mortise is made into both the leg and rail components.
This is typical when using a Festool domino or a slot mortiser. Anyway, I made the mortise into one inside face of the leg, then after the mortise was made into the other leg face I noticed hidden geometry was added to the opposite leg face (outside face) where the mortise is located . I can remove this geometry, add lines and heal the leg.
However, am curious find what happened and root cause of what I may have done. This doesn’t look to be that complex of a design.

I scaled a copy of the leg and tenon components up by a factor of 1000 as recommended by @DaveR but that didn’t make any difference. Also, I created the mortise using Trim and Keep plugin but intersect faces with selection yielded the same result.
I am attaching some screenshots and the skp file. The leg in the .skp file is the component copy that has been scaled up by x1000.

As always, any help is greatly appreciated.

curve leg cab stand~.skp (335.7 KB)

Looks like the extra geometry (those hidden diagonal edges) are required because of the difference in the curves between the front and side views.

Of course it’s your design but I would probably make the curves all start at the same height on the leg.

As always, thanks for responding.
As I look back now, without my layout lines, it is possible I created the curves starting at different heights up from the leg bottom. Its hard for me to tell now.

  1. Did you spot this by seeing that the curved portion of the leg has the hidden geometry on the adjacent faces start at different heights ?
  2. If the mortise is added at the section where the leg faces are flat , well above the curved portion, why is the extra geometry needed ? As I noted, extra geometry was only created when the second mortise was added.


Sometimes you butt heads with the built in tolerances of the software. Running some sort of operation like Intersect Faces or Trim and Keep forces SketchUp to parse through all of the geometry in the component and it will do a repair to fix the issue. If you leave Hidden Geometry hidden, it won’t show and shouldn’t really be a problem. I guess I would consider the overall shape. It’s it’s what you want, leave it.

FWIW, look at the way the hidden geometry in the curved section is so different. Would probably be better to use the same number of segments for all the curves. Best if the vertices coincide from one face of the leg to the other but not always practical.

Thanks again for providing your in-depth understanding. When I would draw this by hand with a lofting stick, its possible the inside and outside may also have been at slightly different heights.
I’ll certainly be aware now best practice is to start curves at the same height. Still experimenting and learning to draw these double curved legs and use Fredo spline.

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I’m sorry. Maybe I gave the wrong impression. You don’t necessarily have to start all the curves at the same height. It can be easier for some things, though. You should design it the way you want it to be.

Thanks for clarifying. Yes, I’ll see what works for a particular design. Another possibility, if a design does have these differences in inside and outside curve heights, and extra geometry is created when mortises are made. Maybe best to save a version of the leg before the mortises are created. That way it can be used for the leg template and the mortised version of the leg can be used for other parts of the plan like exploded views.

It may be that the extra edges won’t affect things anyway. You might also experiment with cutting the mortises before shaping the leg. You would likely do that in reality, right?

Yes, the shop process is mortises are cut first than the parts are shaped. Differs from SketchUp way I learned, with your help, to draw using with as many parts insitu then add joinery.

Adding the second mortise added the extra edges but also smoothed the edge on one corner of the leg. That needed to be corrected or the leg didn’t appear to look right.
I went back and made that corner edge visible again and kept the other added geometry.
As you said, It may be that the extra edges won’t affect things anyway.

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