I'm comfortable with the process of creating and joining wood with dowels, but I'm not sure what size dowels to use in which cases? Specifically, I'm working with 1" thick stock (3/4" actual), what size should I use?
What are the other sizes and lengths of dowels used for?
Are there any recommended grouping or spacing for wood dowels?
When dealing with joinery I typically always deal with thirds. So I'd get whatever is closest to 1/3" that I can get. 3/8" is probably good for this, 5/16" even better. Thirds is a pretty good rule of thumb especially for furniture sized joinery.
This can be applied to all types of joinery such as mortise and tenon, splined miters, bridle joints, etc.
The best work I know of on the topic was written by Tage Frid (see http://amazon.com).
The approximate rule-of-thumb, iirc, is to use a dowel no more than 3/8 the thickness of the wood to be joined (and not less than 1/4 the thickness).
For example, if you are joining 5/4 boards (finished thickness 1"), the dowels should be between 1/4" and 3/8" in diameter.
Likewise, if joining finished thickness 3/4" boards, use between 3/16" and 9/32" diameter dowels.
This presumes, of course, you're joining the boards on the narrow dimension (e.g. making a door frame).
Forget about “rules of thumb”. Following them you could end up with 3/4” dowels for two by four size of wood, which would not last long due to dowel shrinkage over time. I would advice to stick to no larger than 3/8” dowels for any wood thickness and put them in several rows in thicker pieces.
