Pin Routers by Jim Adams
A pin router is a routing machine in which the cutter is guided by a stationary steel pin. Before the development of CNC, pin routers were used extensively in industry as template followers and duplicating machines.

I use a simplified, home-built version of a pin router for rounding over the edges of small intarsia parts. This set up offers major advantages over other roundover methods. One is that the pin, being very small, can guide the bit into inside curves and sawtooth patterns where no sanding drum or bearing-piloted router bit can go. Another advantage is that the pin, being stationary, cannot burn or damage the workpiece.

The photos show a home-built pin router and some of the cuts you can make with it. Here are some notes on building and using these machines:

1. For safety, the hole through which the router bit protrudes must be close to zero-clearance. A larger hole can allow a small workpiece to tip in - a dangerous situation.

Home-built pin router

2. Use a full-size router, at least 3/4 hp. The guide pin is a 1/16" pin punch. Router bits are point-cutting roundover bits. In my work, the most useful sizes are 1/8" radius and 3/16" radius (you might have to order them).
3. The table and overarm have no set dimensions. In my tables, the overarms are 1 1/2" square. Mounting blocks are 1 1/2" thick (2 x 4s). Throat depth is about a foot. Overall construction is square, strong and rigid. The tables are mounted chest high, so you can see what you are doing.
4. The arm is held to the mounting block by a pair of " carriage bolts with flat washers and wing nuts (see photo). To allow for adjustment, the bolt holes through the arm are drilled oversize. A scrap of sandpaper is glued to the mounting block between the bolts. The arm is positioned so the pin is centered over the router bit, and the wing nuts tightened tight. The sandpaper prevents creep.

Point-cutting roundover bit. Arrow on the table indicates feed direction.

5. To make an inside cut requires several steps. First, turn the router off. Raise the pin. Place the workpiece over the router bit. Lower the pin. Start the router and make the cut. Turn the router off. When the bit has come to a complete stop, raise the pin and remove the workpiece.
6. Finally, pin routers are useful for undercutting backboards. I use a 1/16" pin and a 1/8" straight cut bit (see photo). When making multiple copies of smaller projects, I glue the projects to luan like so many cookies on a cookie sheet. When the glue has dried I rough-saw away most of the scrap, then finish up on the pin router. Quality is excellent, though the process is not as fast as one would wish.

Hand position for a small part. The part is rotated counter-clockwise against the pin.

These parts (a wolf's nose and an eagle's foot) were rounded over on a 1/8" radius pin router.

Assembly detail. Sandpaper prevents the arm from creeping.

Pin router set up for undercutting backboards. The pin is 1/16", the bit 1/8".

 

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