I wanted to practice collaring some scrolls together, I think the end result came out well, but using round bar made it really hard to get a tight fit.  Next time with square.  Build video:

 

 

 

Looks really good. You light look into making a collaring vise to keep everything tight when closing the collar. 

I will have to look into it, sounds like something I need

Take a looks at the second Mark Aspey book. Tells you everything you need to know about traditional joinery and how to make the tools you need. They’re sort of pricey but the best, easy to follow smithing books I’ve seen. 

Collars are typically closed around the items they are going to hold together whilst the collar is hot, the reason being that as they cool they shrink & grip tight. The collar material length is also usually pre-calculated so there is no overlap when folded around, or exessive gap between the butting up seam lines. Sometimes the ends of the collar material stock are tapered so if the material does overlap a little, the overlap isn't visible & the collar maintains the same thickness above the items being collared.

In your video you seem to have forged it cold and have a large overlap, both will prevent a tight fit. It also seems like the central bar is thicker material, which creates a high point and gap under the collar & arguably doesn't help your cause.

I have posted this video elsewhere on the forum in the past but it might help you as it contains theory as well as tooling ideas. A "bad language alert" seems to be the done thing around here to prepare the youthful and/or more sensitive souls.