I recently used a method I found on the internet, a bit of steel plate with a 15mm hole drilled through it, the hole was around 10mm from the edge and I then hacksawed an angled cut down into one side of the hole, the long side of the slot was then bent with a cold chisel a little out of line and that was the tool,
Cut pieces of oak around 16mm square and anything up to 18ins long, trimmed to fit into chuck of a battery drill and front end pointed to poke into the hole in the plate, spin up the drill and lean a bit on it and through it goes producing nice round dowels and long stringy swarfe. The dowels to my mind were perfect as they had a pronounced spiral groove finish which was a little rough and I think would hold glue nicely, however I also did a few where I cupped some sandpaper around it whilst still in the drill and got nicely finished dowls but obviously undersized,,I just drilled smaller holes to suit these. The steel plate was very easy to knock up, Describing it makes it sound complicated, look for it on the internet, seeing it explains it simply which I cannot! Now my only concern would be if it would work with 20mm plus stock?
Btw, just as a matter of intrest, I think that in lots of situations the oak dowels are not nessesarily round, square pegs with corners roughly trimmed are knocked into round holes, the peg/hole deforming into a tight fit,,,is that correct or is it something Ive just drempt up!
Steve.