My lathe turning experience is nil, but the product featured in the videos below is in my inventory of tools. 

The guy's a bit slow getting to the red meat, but well worth waiting for.

 

 

Neat device, Gene. Looks very precise.

 

The guy ties a pretty good bowline knot, too!

They are VERY precise, Lew. 

I've been using both sets for several years. 

Have you seen the Segeasy?  People on another site swear by it.  There are four videos here and the last one shows how to build the sled.  It has been said the drafting 45 degree and 30-60-90 degree triangles can be used to set and test the sled when you are done.

http://segeasy.com/segeasy.htm

 

I built a Segeasy sled about a month ago. Probably took less than an hour. I also order some of the segeasy segments. When I was done with the sled, I put a segment in, adjusted the two fences and cut some segments from scrap wood. Lined the segments up to make a circle and held them in place with a rubber band. I held the ring up to the light and couldn't see daylight anywhere. I was pleased with how accurate the sled was. Have used it a number of times without any problems.

 

Terry