I have a project that I've been asked to make and need some advice on planning. What I need is to know if there is any formula or general rule of thumb for how long to make the straight lengths in the bar before I begin the twist in a bird cage (basket cage) twist.

 

I know there are a lot of variables to consider including the size of bar, length of twist and overall diameter of the finished twist. It's too much for this newbie smith to wrap his head around.

 

I've seen some really good videos on the process being done, but can't seem to locate any data on how to lay out the twist. If anyone has some thoughts, they would be greatly appreciated. If not, looks like trial and error until it works out.

Best bet on something like this is to make samples to figure out the lengths needed.  As well it gives you practice producing the basket twist.  Usually the more times you make something the better you get.  You also end up with a sample to show future customers if it works out.  If it does not work out, you would have had to re make it anyways.