I have often found the need for different threaded knobs, either with a nut or a bolt, for some of my projects. While these may be available for purchase, it's a lot faster, easier and cheaper to design and print your own. For this project, I designed and 3D printed a set of knobs using 1/4-20 nuts and bolts from my local hardware store.

I plan on using these as quick attachments on my workbench to secure different tools, fixtures and other equipment while I'm working.

The STL file for this part is available for download here

Step 1: Measure Your Hardware

I bought several 1/4-20 hex bolts and nuts from my local hardware store. The first step in designing the knobs is to measure the parts. If you don't have a set of calipers, most standard hardware can be found on McMaster.

The standard dimensions are:

Bolt Head Distance Across Flats: 0.432"
Bolt Head Thickness: 0.153"
Bolts Diameter: 0.238" (just use 1/4")

And for the Nut:

Nut Distance Across Flats:0.431"
Nut Thickness: 0.215"

Step 2: Model the Knob Shape and Revolve

The next step is to create the 3D model, and I used the Revolve function in Fusion360. Open the program and start a new component and create a sketch on any of the planes. This knob is designed to be 0.4" thick and have an outside diameter of 1.5" and a clamping surface that is 0.75" in diameter. Remember that when working with a revolved object, the dimensions in the sketch are the radius, not the diameter, so cut those numbers in half. Us the vertical edge of the sketch to create the revolve.

Step 3: Cut Out the Pockets in the Knob

With the solid body created, the next step is to cut out the pockets for the hex-head of the bolt, or nut, and the through hole to accept the threads. Create another sketch on the top surface of the knob, and use the polygon tool to create a hexagon sketch on the surface.

I oversized the distance between the flats to make sure I had an easy fit for the hardware, as well as a space for the epoxy to go when I glued everything together.

Create another sketch on the bottom surface, and cutout a circular hole big enough to accommodate the threads of the bolt. I used 0.26" to make sure there was an easy fit when screwing the knobs together.

Step 4: Design the Shape

With the critical features of the hex pocket and the through-hole complete, we can move on to the more artistic part. I wanted these knobs to have a unique look, and decided on a 3-lobe, triangular design.

To make this shape on the outside:

Create a sketch on one of the horizontal planes
Draw a circle with the origin on the horizontal axis
Make the circle tangent to the bottom circle
Use the Circular Pattern function to instance the circle around the origin
Exit the sketch and extrude the shapes through the knob

With the final shape complete, add fillets on all the sharp corners to smooth out the print and make a part that's nice and smooth to the touch.

Step 5: Mixing Epoxy

I skipped over the 3D printing, but ... do that. This part is designed so that it can be printed without any support material. The overhang is at 45 degrees, so check the settings in you slicing software.

Next, lay out some tape on a work surface, and mix the epoxy to hold the hardware into the printed parts. I used a 5-minute epoxy that you mix in 50-50 ratio, using a popsicle stick to mix. Open a window, this stuff is foul smelling.

Don't forget to cut the bottle open...

Step 6: Epoxy the Bolt or Nut

Apply the epoxy to all six sides of the bolt head, or the nut. Be careful not to get any on the inside threads of the nut, or the parts will be very difficult to thread together.

Slide the hardware into the knob, and leave it somewhere to cure where the hex pocket is facing up, otherwise the epoxy will run out. I used a beer bottle to hold the bolt and knob upright.

Step 7: The Finished Product - Check the Fit

That's it, once the epoxy cures, thread the nut and bolt together. If any epoxy got on the threads, just turn the bolt firmly through the nut to clear it out. I plan on using these knobs to hold together fixtures and jigs on my workbench, but they can easily be modified to create doorknobs, drawer pulls or other handles.

Thanks for reading!

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