[Henry the Hermit]

While not steel, here is how I made aluminum bent-rod frames. 1/4 inch is OK for light tubes, but I used 5/16. If you want to build Chinese style for looped tubes, you would most likely need some heat to bend the eyes.

http://panamaretire.net/slingshots/biombos/aluminum/how-to/index.html

 

[Henry the Hermit]

Add: I bet you could use the same basic tools to bend steel rod with heat.