Lock blocks are adjustable nuts. I first learned about the concept when granthams sent me some of his smart nuts to use on my bowl press. They are drilled and tapped in such a way that they slide on a threaded rod when tilted but tighten in place at their stop.
This project is designed to be built with a drill press, vice, and three self made fixtures. The three different fixtures are described and their dimensions are shown in the attached pdf. They are made of ½" medium density fiberboard. (MDF). It is readily available at your home center or hardware store. MDF is an excellent material for making fixtures and you will find many uses for the leftover stock. Any fixture you make from MDF should have finish applied to keep it from absorbing moisture.
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Step 1: Lock Block Theory 101
A lock block is made from a 1" cube with a ⅜-16 threaded hole in the middle. The another ⅜" hole is bored at a tilt of 12.3°. What this does is remove most of the threads except for one side at the very top and the other side at the bottom. This allows the block to slip down the bolt rod and only lock into place when it hits a hard surface.
Step 2: Obtain Material
These blocks can be made from most anything. They can be made of metal if you have the proper tools. I have made them from Acetal, HDPE, or PVC plastic but most of the time I made them from hardwood as wood is more readily available for everyone. You will need 1" cubes of a tight grained hardwood. Hard maple or beech are good choices. You need to either cut suitable wood to make your own or buy prefabricated wooden cubes. I purchased mine via the Internet and I paid only about $20, including shipping, for 100 cubes. This company's wood craft products are always well made with consistently good quality. I can get 500 for about $50 and at a dime apiece, I am not interested in cutting and prepping my own.
Step 3: Drill Center Hole
First you need to decide what face of the cube on want to drill. Any is fine as long has it is not the end grain. Place a mark on that side for registration. Fixture #1 allows for accurate hole alignment in the center of the cube when used with a drill press vice. It is made of a 1" thick piece of MDF.(Two 1/2" pieces glued together.) It is 4" long and 1⅜" wide. Using the measurements shown at the end of the article, cut out the fixture. You will also need a 2" by ¾" toe piece of ½" MDF to glue on the left side of the fixture to reference it to the vice. Install a 5/16" brad point drill into your drill press. Find and mark the exact center of the cube face to be drill. Adjust the position of the vice until the point of the drill bit touches the center mark and clamp the vice in place. Now drill as many as you need.
Step 4: Tap Hole
Fixture #2 is not entirely necessary but it does speed up the tapping of holes. It is constructed or five ½" MDF piece, each 1⅛" wide. The fixture pdf gives the specific dimensions.for all pieces. Glue them together to form your fixture
Before tapping each hole, put a touch of paste wax on the tap. It makes for easier tapping and better threads.
Step 5: Add Tilted Clearance Hole
Fixture #3 allows for accurate placement of the cube and also tilts it 12.3° for drilling. It is made from a 1" thick piece of MDF, 4" long and 1" wide. Again specific dimensions can be found in the fixture pdf.
Mark a line 13/64" away from the edge of the cube. Place a 3/8" Forstner bit or end mill bit into the drill press and align the vise until the edge of the bit just touches the line. Lock the vice in place and drill through.
Step 6: You Are Done
Just give each a dunk in some mineral oil and they are ready to use. Remember since they are wood and the bolts are steel, they will wear out. But with your three fixtures you can easily build some more. At craft shows these sell these all day long for a dollar a piece. I wouldn't be surprised if they show up on Etsy,