Stumbled on this old thread while trying to answer the same question about which 3M filter, here's what I found in another place - "Hello. Thank you for contacting 3M regarding personal protective equipment. The recommended filter for welding on hexavalent chromium or zinc is the 2097 or 2297. ...

There are lots of good free CAD programs out there, Google Sketchup being a real favorite. Nothing I know of is specialized for 3D tube structure.

Another at the same site, a lot more beveling at the base -



http://www.cycle-frames.com/bicycle-fra ... T-SET.html

I later found these at a bicycle frame builder's website - http://www.cycle-frames.com/bicycle-frame-tubing/SEAT-BINDER-AND-BOLT-PREMITERED.html http://www.cycle-frames.com/bicycle-frame-tubing/images/P/NOV_500A_BB_SET.jpg And it'll probably work for my purposes here. It just seems like it would be ...

I have some split tube I'd like to weld bolts to. What are these things called & where would I find some weldable lugs? Is there a trick for fabb'ing something simple? Considering cutting some coupling nuts in half & drilling one side out. Ideas? I've Googled the bejeezus out of pinch bolts,...