Okay,

Here is the issue. Make two helices. One inside the other (mine was 12mm OD with 10.268 ID) Set them at a 1mm pitch no draft. Offset the ID so that it supports the 1mm pitch. Draw in a line between the two start points (I drew a triangle but you don't have to). Sweep along two rails and look at the mess you get. My helices where 18.5 mm long by the way so that you can get a better idea of what is going on.

It does not on no less than six attempts stay inside the rails. It sags, it over shoots and all sorts of mischief but a nice straight tight surface between the two lines of the helices it does not do. Have bad tolerances rather tight and not change. Have checked and senn if there was issues with the helices according to VCPro v9 and no joy.

I did find a work around and was able to move forward on the project but that is time lost and since it is a part to repair a machine. Please don't offer the boolean subtraction as that did not work either as it left surface planes in the final threads and really made the final drawing on a 2D look really bad. Work around was boolean addition and while it worked there are still issues Not completely centered even when setting tolerance in microns. -Michael

Martin will set up a file that does the same thing and post it in a bit as needing to get some other work done. -Michael

I was going to up load the file but a security token is missing and it will not allow me to up load. -Michael