"Pass me the calipers" I said.
I make all my wood nuts at TechShop.
Step 1: You Will Need
- 3D modeling program (I used Autodesk Inventor)
- a CNC router (I used a ShopBot)
- 1/8" router bit (ballnose)
- 1/2" router bit (I don't care what shape, whatever makes you comfortable)
- Wood glue
- Basic woodworking tools
I have opted to use poplar wood for this project. Though it is a bit softer than maple (the typical wood of choice for threaded parts) the very coarse threads with a 2" diameter make for a robust shape that requires minimal edge-holding properties.
Step 2: Taking the Dimensions of the Screw
Step 3: Modeling the Nut
- Start by sketching the profile of the thread
- Extrude a block that will make-up the body of the nut
- Define the center axis of the coil
- Enter the values of the coil (the threads)
- Fill-in the coil with an extruded circle
- Alter the features of the block extrusion to render the two halves separately
- Now fillet all the interior corners with a 1/16" radius, since that will be the radius of the tooling for the final part. This won't change how the part is finished but will give an accurate rendering of it.
Herein lies the guesswork. The negative space in the nut has to be slightly larger than the screw to allow the parts to move freely what since we live in a universe of friction and not idealized Platonic structures. I settles on adding an extra .1" to the diameter, giving the screw an extra .05" of wiggle room in every direction.
Step 4: Machining the Parts
Step 5: The Moment of Truth
You can go fancy with this part, using any manner of dovetails and tenons, but really a little bit of wood glue is all you need. The nut will fit into the leg of the workbench tight enough that structural integrity shouldn't be an issue. I planed it down a bit more to better fit its nook in the bench.
The screw spins freely but tightens-up and stays tight when clamping its business.