I've made one.
After writing about my "sliding doweling jig" (based on a jig I saw in Fine Woodworking), I heard from a number of people that complained that: (1) They had difficulty drilling perfectly straight holes that are 1-1/2" deep and (2) They've had trouble locating the spacers I use as bushings.
I've also thought long and hard about doweling jigs and how I could improve my design. To make it more universal, so that it could be used in table stretchers and face frames and cabinet carcases alike.
While I was doing my thinking, I discovered that Rockler now sells an inexpensive doweling jig (only $9.99 as of this writing). Here, this one:http://www.rockler.com/product.cfm?page=18059&filter=dowel%20jig
It is simply a hardened drill bushing with two 3/8" holes, attached to a transparent guide featuring center lines. Rockler seems to really be pitching it for face frames.
So I purchased a couple of them to experiment with, and I've come to the opinion that it actually ideally suited to all sorts of doweling tasks. With a little modification, that is.
The clear plastic guide has got to go. First, it is too slippery and when clamped to the workpiece is inclined to allow movement while drilling. Second, I don't like referencing from the center of the holes of the guide. I prefer to reference from the edges of the steel bushing instead.
So I made three new hardboard guides to replace the original transparent guide. Each board is sized according to its use: (1) This first guide is for face frames, and is 1-3/4" wide and 4" long. All my face frames are 1-3/4" wide, and the steel drill bushing is 2" wide. So using the edge of the steel drill bushing as a reference won't work. BUT, by attaching a 1-3/4" wide hardboard guide, I can now use the edge of my shop-made guide as a reference. I simply align the edges of the guide with the edges of my frame member, clamp, and drill my two holes. I don't think it could be any faster.
(2) The second guide is for edge-drilling cabinet pieces, and is 2" wide and 4" long. It is a little redundant, as the 1-3/4" wide guide would have sufficed. At the time, I supposed the extra width would help in gripping the workpiece. But with the use of the non-slip stair tape (see below), that really isn't a concern.
(3) The third and final (so far) guide is for face-drilling cabinet pieces, and is 2" wide but only 2-1/4" long (so it extends only 3/4" below the bottom of the steel drill bushing). This allows me to drill face holes in cabinet pieces.
Each of my shop-made guides has non-slip stair tape covering it entire face. The non-slip tape extends all the way under the steel bushing. This tape provides a death grip that prevents the bushing from moving while drilling.
While doing cabinets, the two pairs of outside holes (flush front and flush back) are easy, just align to the edge of the steel drill bushing, clamp, and drill. For holes in the center of the panel, simply use your combination square to locate the steel bushing. You can easily drill four sets of two holes with a single combination square setting (one referencing the front edge of the piece, one referencing the rear edge of the piece). If you need more, use two combination squares, or make a jig that references from previously drilled holes.
I've included some pictures showing the unit in its various configurations (under use), and some of the results. I'm extremely happy with the outcome. Edges are perfectly aligned, and it requires minimal effort to achieve excellent results. Cost is nominal, and the design is flexible enough that I can easily add spacers for things like offset joints.
I'm happy to have another alternative to joining wood that is strong, flexible, and very inexpensive.
I have concluded that a drill bushing with two holes is actually ideal when it comes to flexibility. You'd think two holes is going to require excessive repositioning. That, four or five holes would be wiser. In reality, though, I don't often want to run a line of four or five holes in a row, you don't need that many closely spaces holes in a cabinet joint. And for something like an apron to leg joint, it is easy to get four holes with a single move of the jig, and the holes are arranged symmetrically in the joint. And for face frames (where two holes is obviously ideal) you don't struggle with a bulky jig that wants to fall off the frame member while you're trying to clamp it.