dowel drills

I believe wrightwoodwork did just that, made exterior doors. How are they holding up wrightwoodwork?

I feel that depending on your construction techniques and particular application the 16mm x 75mm dowels may work.  But for example, if you're profiling your stiles and rails on a shaper and the groove depth on the sticking is around 1/2 inch your dowel will only penetrate into the stile approximately 1" more or less. In this instance I would not feel comfortable in an exterior application. However for interior doors in a climate controlled environment that may be fine if an adequate amount of dowels can be placed in each joint. So it really depends on the specific application and joint design of your project. 

I'm still experimenting myself. 
  
The doors are holding up fine had no complaints so far I made basic frame a bit like a 4 panel door layout then it was overlaid with ship lap linning boards which was screwed to the face of the frames. Doing it this way added a bracing element to the door. So the door construction is no solely relying on the dowels to do all the work. When making things like this I feel that everything has to work together and if executed correctly can make a joint like a dowel strong enough to meet its service demands in use. Also the type of glue that is used can also make a difference in its service . The modern pu glues are not soaked up into the end grain of the time as the molecular structure of some of these glues is larger than the molecular structure of some timbers preventing them from being soaked into the end grain also sealing the end grain can also help to prevent the glue being soaked up as well . Then there is glues like casimite which are non shrinkable and once set have no flex which are similar to the type of glue used in structural use that will be 2 part glues. If I was going to dowel a scribed shoulder and tennon door I would cut the rails the length they would need to be to allow for the scribed shoulders, but not do the scribe apart for about an inch or 25mm so the rails had the appearance of being scribed. Then on the stiles I would remove the profile, but leaving rough an inch again so it still appears that the shoulders have being scribed to the stiles. Like what would have being done before the use of tennon machines. What is called a franked shoulder I think. Another thing that maybe could be done to add strength to the dowel joint is to mark a line where the dowels go then either using a metal star dowel hammer it through the face so it goes through into the dowel or drill say a 5mm hole for a dowel to again go through through the 16mm dowel. Will need to experiment on that idea. Like I say it is all about clever design and looking at things as a whole. Take tji joists there just 10mm osb with a ply like top and bottom flange that are used floor joists and weight to weight are able to cover larger clear spans with less weight and are just as strong. The flooring also adds to there strength. Try to walk on them they are totally rubbish as they have no strength in side to side movement bit only straight down. If you look at the clearance one the the top of the doors you can still see that it is parallel showing that they have not dropped