How to Design and Print Replacement Knobs for Appliances

Why this is one of the best functional prints

A replacement stove knob from the manufacturer costs $15–30. A replacement HVAC knob? Often discontinued entirely. Washing machine knobs crack and the model number leads to a parts page that says "no longer available."

A 3D printed replacement costs maybe 50 cents in filament and takes under an hour to print. More importantly, you can make it any shape you want. Easier to grip, bigger for arthritic hands, a different color, with a pointer that actually aligns with the markings. I've printed knobs for a stove, two washing machines, a dehumidifier, and a vintage stereo receiver. Every one of them is still working.

The process is the same every time: measure the shaft, model around it, print, test fit, adjust if needed. Once you've done it once, every broken knob becomes a 30-minute project instead of a parts-hunting headache.

Measuring the shaft

The shaft is everything. Get this wrong and nothing else matters. You need a caliper (digital or dial, either works). A ruler won't cut it for the tolerances involved.

Common shaft types

What to measure

For a D-shaft (the most common type):

1. Shaft diameter (the full round dimension, typically 6mm for stoves)
2. Flat width (the distance from the flat face to the opposite side of the round)
3. Shaft length (how deep the hole in the knob needs to be)
4. If the old knob exists: outer diameter, height, any pointer or indicator positions

Write these down. Then measure again. A 0.2mm error in shaft diameter is the difference between a knob that clicks on firmly and one that wobbles or won't fit at all.

Modeling the knob

You don't need Fusion 360 expertise for a knob. You can generate one in a few lines of OpenSCAD, or use a parametric generator on Printables.

The fast way: parametric generators

Search "parametric knob" on Printables. There are dozens of designs where you input your shaft diameter, flat width, knob outer diameter, and height. The generator creates the STL. No CAD skills needed. The parametric D-shaft knob on Thingiverse is another good starting point.

The manual way: Fusion 360 or TinkerCAD

For a D-shaft knob in Fusion 360:

1. Create a cylinder matching the shaft diameter
2. Create a rectangle wider than the cylinder, positioned to cut a flat
3. Boolean subtract the rectangle from the cylinder. You now have a D-shaped hole.
4. Extrude the knob body around this hole (a larger cylinder or whatever shape you want)
5. Add a pointer ridge, knurling, or grip texture to the outside

TinkerCAD works the same way with its shape-subtract tools. It's simpler for beginners but less precise for tight tolerances. For knobs where the shaft fit has to be exact, Fusion 360's parametric dimensions let you adjust by 0.05mm increments until the fit is right.

For inspiration, this walkthrough on designing potentiometer knobs covers the full Fusion 360 workflow with specific dimension logic for D-shaft fits.

Choosing the right material

Material depends on where the knob lives.

Drawer pulls, cabinet knobs, dresser handles: PLA. Room temperature, no stress, no heat. PLA's stiffness actually helps here because it clicks onto the shaft firmly. Print in any color. Sand and paint if you want a finished look.

Appliance knobs away from heat (washing machine, dehumidifier, audio equipment): PLA or PETG. PLA works if the appliance doesn't sit in direct sunlight or near a heat source. PETG adds some insurance against heat.

Stove and oven knobs: this is where material matters. Stove knobs sit near the cooktop surface, and while they're not directly over the burner, radiant heat from adjacent burners can push surface temperatures to 50–70°C. PLA softens at 55°C. ABS (heat deflection around 98°C) or ASA (around 100°C) is the safer choice. Both need a heated chamber to print without warping. A printer with an enclosure like the Q2 at 65°C chamber temp handles ABS and ASA reliably.

A cautionary note about stove knobs: the knob itself doesn't touch the burner flame, but if it's on a gas stove directly adjacent to a lit burner, measure the actual surface temperature with an infrared thermometer before committing to a material. I measured my stove knob at 48°C during heavy cooking. PLA would survive that, barely. ABS gives a comfortable margin. For a full ABS vs ASA heat comparison, that guide covers the thermal properties in detail.

Printing and fitting

Print settings

Tolerances

This is where most first attempts fail. The tolerance guide from 3D Chimera breaks down the relationship between design clearance and functional fit.

For D-shaft knobs, start with 0.1–0.15mm clearance on each side of the shaft (so if the shaft is 6.0mm diameter, model the hole at 6.2–6.3mm). This gives a snug friction fit. If you want a tighter press fit, go to 0.05mm clearance, but you may need to sand or heat-press the knob onto the shaft.

If the knob uses a set screw, design the shaft hole 0.3–0.4mm larger and add a hole for an M3 grub screw perpendicular to the shaft. The screw clamps the knob to the shaft. This is more forgiving of tolerance errors and lets you remove the knob later.

Print a test cylinder with just the shaft hole (5mm tall, same hole dimensions) before printing the full knob. Takes 3 minutes and saves you from wasting an hour on a knob that doesn't fit. If the test is too tight, increase the hole by 0.1mm. Too loose, decrease by 0.1mm. Once the test fits, print the real thing. For broader functional print ideas, knobs are just the beginning of household repair printing.