Hi Yenmonger - if you turn off the "Maintain Height" sweep option it appears to behave better:



I'm not sure what's going on with the problem situation, but it probably has to do with your rail curves taking a sudden sharp bend at the tip, and especially with having their end tangents pointing exactly towards each other.

The way sweep works involves making a kind of plane between the 2 rails, and one part of making that plane is to average the curve tangents together. Tangents pointing exactly towards or away from each other make for a degenerate average which probably makes for some chaotic framing behavior in such areas. The sweep frame probably wiggles around in odd ways right there.

You'll probably get better behavior by not having that sudden inward bend at the end and instead using fillets to make a tight round in that spot instead.

- Michael