GearHeads Corner

I'm seeing a few glitches in the stl files generated for bevel gears.

I'm only using simple software that doesn't seem to be able to repair them properly.

When I load a bevel gear into Netfabb Studio Basic 4.9 (the free version), it shows a strange line through the gear, see attachment.  Even after repairing in NetFabb, the line still appears.

I've ignored this up to now, but it has caused some applications to crash and produce funny results.

Closer inspection in Blender shows what looks like overlapping triangles, see attachment. 

It doesn't appear to be a completely duplicated triangle - if I delete one of the overlaps, it reveals a hole through the object, see attachment.

This was done using a straight bevel, mod 1, PA 20, 14 teeth, 4mm hole, 5mm face.

Seems there must be a bug in my triangulator code. Ill search for a why on it, the bevels Ive tested so far dont seem to have the line, or at least
the software I use hasnt reported it. Bevels are the most complex for obvious reasons and Ill do a search for what could cause the lost triangle..

Thx
Art