Hi,

I was testing a few things and I came across something weird to say the least. Here the file. The red surface seems problematic and I wonder why out of curiosity of course?

I did a one rail sweep of the profile curve and used a scaling rail to generate a surface of which the red face is part. All curve are named and I also did a rebuild on both rails so they have the same number of control points, I thought it would help but it didn`t.

Thanks,
Felix

Hi Felix - those weird areas are spots where the scaling rail is not coming into effect or kind of jumping because it has a kind of ambiguous case to deal with.

One problem at the tip is that the scaling rail does not quite extend the full length of the rail, if you zoom in on the tip you can see this:





Also on top of that, just in general the scaling rail mechanism does not work well when you try to make the scaling rail swoop inwards at a 90 degree angle to the main rail. The scaling rail mechanism needs to find intersection points on the scaling rail from the main rail, and that doesn't work very well when the scaling rail swoops totally inwards towards the rail.

See these previous posts for some explanation on this:
http://moi3d.com/forum/index.php?webtag=MOI&msg=2681.3
http://moi3d.com/forum/index.php?webtag=MOI&msg=1807.7


Then additionally the scaling rail mechanism will have a problem when you've got a profile curve that touches the rail instead of being positioned around the rail.

The way the scaling rail works with a tubular type sweep is like this - say here the circle is the profile, the red curve is the rail and the blue curve is the scaling rail:



The way the scaling rail mechanism works is that it first tries to find a reference point on the profile curve by shooting out a line like this (or really a plane but similar to this) to intersect with it:


Then it also finds the intersection of the scaling rail with the sweep plane at that point and scales the profile by the difference between those reference points from the sweep rail point.

But in your case that intersection method is not going to work well because your sweep profile consists of a line basically in the same spot as the intersection line that is sent out, so that makes for a complicated and overlapping intersection instead of a single point intersection as in the tubular case.

So basically at least right now with the current mechanism you can't use a scaling rail on a profile curve that touches the rail and shoots outwards from it rather than being a kind of semi-tubular shape that goes around the rail.


Instead of using a scaling rail, you can try using a 2-rail sweep instead, and pick both those curves as rails to use for the 2-rail sweep, rather than 1 rail + scaling rail.

- Michael

Hi Michael,

thanks for the explanation. I forgot to mention that I also tried 2 rail sweep and it doesn`t work well either with the same profile. (But it works fine with a 1 rail sweep if I use only the angle curve)

I`ve join the real part this time and I`ll try to explain what I wanted to do. Basically, the scaling rail in the first file is the intersection or edge of the innner recess with the outer shape and it would also be the path a pointed or v shape tool would follow to machine the inner section but assuming this will be done on a 5 axis CNC machine, I need a reference surface at a constant angle to the side of the outer shape (or Z in this case) such that the side of the V shape tool follows the side of the outer shape in that region and the point of the tool follows the scaling rail curve.

I was trying a few things and I came across this bizarre result and I wondered why.

Thanks again for your time.
Felix