Having used and liked the pocket hole machine, I decided to build my own, using a router I found for a song at a yard sale, and with scrap plywood I got at the cabinet shop. The one I made was many moons old, and looks much worse for the wear, so it is modeled and rendered in 3D for your viewing pleasure.
Step 1: Commercial versions and basic use
It is basically a router set up with a handle and a pivot. The picture is the only one I could find, and is of bad quality after zooming in and taking a screen shot.
The basic use of one consists of putting a board (usually) horizontally and the router bit either swings from the top or the bottom and creates an arced pocket so that you can basically toenail a screw into a board and it lets you butt joint two boards together.
Also shown is a picture of what the joint itself looks like- chances are that you have seen this on furniture even if you didn't know what it was.
There are also jigs you clamp on and use a drill with, the most notable being by Kreg. You can make those homemade as well, but I wanted a machine based version with a more dedicated setup. All other options were more expensive than I wanted to invest, so I made my own similar to the bench top model I was familiar with.
Step 2: Materials and Tools
Dimensions will largely depend on your router, but there are some other considerations
(3) pieces threaded rod (there is an alternative design method I will try to remember to discuss that would only need one piece of threaded rod)
(3) wing nuts
(1) hinge and screws
(1) adjustable height support
(1) router mounting plate
Drill or drill press
Step 3: Shaping up your parts
The design of this fixture is such that there is an adjustment plate supported byt hree threaded rods and wing nuts, which allows for the fixation and adjustment of the plate. The sizing of this adjustment plate will be based on the size of the router plate. They should be approximately the same width, and about the same relations as shown in the pictures.
There are intended to be three upright supports or sides. These need to be sized according tot he final size of the adjustment plate. Each side needs to have a straight slot in it to allow for the height adjustment of the adjustment plate.
The base needs to be sized to attach all three sides to, and ideally will protrude as shown to support the workpiece that the pocket is being cut in.
It is important that the work gets clamped down to the base, because the feature of this jig is to make a radial plunge cut into your material, which will not make the material very easy to hold down while manipulating the jig.
I put an elongated handle on the side of mine, which you can either make separate or you can design into the router attachment plate.
Step 4: Assembly
Holes need to be put in the adjustment plate that match up with the slots in the uprights, and threaded rods secured into the adjustment plate. Depending on how you do this, you may have to put the sides together around the adjustment plate and then affix them to the base so as to capture the plate and rods. I drilled holes in the plywood and epoxied the rods in place, then assembled the sides around the adjustment plate.
The hinge needs to be mounted to the adjustment plate and to the router plate as shown in the pictures.
It is best to still use a pocket hole drill bit after you create the pocket, or you can use a drill bit from the opposite side, but you will need to practice lining the holes up so that you don't break your screws.
Step 5: Alternate design
In the picture I have shown the jig with one side removed and one guide. Obviously you would need to resize the slots in the sides to accommodate the supports, but it should be much easier to set up and adjust with this alternate design.
Step 6: Visual aid
As far as operation goes:
-you lift the router by the handle (you would basically be looking at the bottom of the router bit)
-the board you want the pocket hole in goes on the base of the pocket hole machine, and needs to be clamped down
-once clamped, you turn on the router and lower the handle. Because of the swing of the hinge, the router swings into the board, making a sweeping plunge cut, which makes a swept pocket.
You have to adjust the height of the router to not cut all the way through the board and to cut deep enough. It works just like other pocket hole machines, with some examples of other machines in step one.