This is my take on the classic Oliver String Puzzle. It was built from scrap wood, a ring from a previous project, purchased wood beads and rope.

The goal is to remove the ring from the puzzle. My kids and wife found it quite challenging. I would rate the skill level at 3 out 5. If you can't figure it out from the pictures, refer to the video.

Besides the routed slot, I think the puzzle is pretty easy to build. I've also included STP and STL files (last step) for those inclined to 3D print it. You could also purchase a similar version from Amazon.*

*Amazon affiliate link

Step 1: Tools/Materials

Tools:

Table Saw
Router / Table
3/4" Router Bit
Drill Press
3/8" & 1/2" Drill Bits
Sander
Ruler
Pencil

Materials:

Wood: 3" x 3" x 1" Thick
Wood: 1.25" x 3/4" x 6" Long
Wood: 2" x 2" x 3/4" Thick (x2)
Dowel: 1/2" Diameter x 1.25" Long
Dowel: 3/8" Diameter x 1/2" Long
Rope: 1/4" Diameter x 24" Long
Wood Glue
Metal Ring: 2" OD, 1.5: ID
Wood Beads: 1" Round
Finishing Oil

Step 2: Drawings

You will be building to this drawing.

Step 3: Base

The base is pretty straightforward. Cut a 1" thick (or more) piece of wood to 3" x 3". Mark the center location and drill a 3/8" diameter hole.

Step 4: Post

I used a router table and 3/4" bit to cut the slot. I started with a longer piece of wood and cut it down to 5" long with the slot placed per the drawing. Note that the router table is new for me. Without it, I would have just glued individual pieces together to make the slot. Note that the rounds at the top and bottom are not needed.

As with the base, mark a center location on the bottom and drill a 3/8" diameter hole 5/8" deep.

Step 5: Post/Base Pin

Cut a 3/8" dowel to 1.25" long.

Step 6: Puzzle Build

The pin provides additional support for the post. Glue the pin into the base as shown. Next apply glue inside the post hole and bottom side of the post. Orient as shown. Use a wood clamp to provide additional pressure to the joint.

Step 7: Ball

I purchased a bag of these 1" round beads a while back to use on my other puzzles. Drill a hole through the center. Clamping the bead in a fixture makes this job easier.

Step 8: Blocks

These blocks need to be thin enough to slide through the slot in the post. I started with 3/4" thick wood and sanded 1/64" off each side. The counterbore is used to capture the knot. The chamfers are optional - just me playing with my router. Note that last chamfer is added at the end of the build.

Step 9: Block - Option 2

If you look online, you will notice that most of the puzzles use round blocks. I built some from dowels but I didn't care for how they looked.

Step 10: Add String

You are now ready to build the puzzle. Cut a piece of 1/4" diameter rope to 2 feet long. I melted the ends so it would thread easier. Thread the puzzle as shown. Tie knots in the end and pull the knot into the block. You could leave it this way or go ahead to the next step. The ring doesn't need to be added at this point.