DIY Precision Assembly: How to Design and Install Custom Hardware Spacers for Small Projects

Ever tried to line up two tiny parts and ended up with a wobble that makes you want to pull your hair out? That’s the moment I realized a good spacer can be the difference between a solid build and a frustrating mess. At Spacer Solutions we love turning a simple idea into a reliable piece of hardware, and today I’m sharing the exact steps I use to design and install custom spacers for those small projects that demand precision.

Why Spacers Matter

A spacer is nothing more than a short piece of material that sits between two parts to keep them the right distance apart. It sounds simple, but the right spacer does three things:

Keeps alignment – no more tilted brackets or mis‑aligned gears.
Absorbs vibration – a little bit of give can protect delicate components.
Provides clearance – especially important when you have wires, heat sinks, or moving parts nearby.

If you skip the spacer or use a generic one that’s too long or too short, you’ll end up with stress points, loose screws, or parts that just won’t fit. That’s why a custom spacer is worth the extra few minutes of work.

Choosing the Right Material

The first decision is what to make the spacer out of. Here are the three most common choices I reach for in my workshop:

Metal (Aluminum or Steel)

Pros: Strong, heat‑resistant, can be machined to tight tolerances.
Cons: Heavier, may need a tap for threads.

Plastic (Delrin, Nylon, or PETG)

Pros: Light, easy to 3D print, good for low‑stress applications.
Cons: Not as heat‑resistant, can warp if printed poorly.

Composite (Carbon fiber‑filled nylon, fiberglass)

Pros: Strong like metal but light like plastic.
Cons: More expensive, may need special tools to cut.

For most small DIY projects I stick with aluminum if the part will see any load, and I reach for a 3D‑printed nylon spacer when I need a quick, cheap solution.

Designing Your Spacer

Measure Twice, Sketch Once

Start by measuring the gap you need to fill. Use a digital caliper – I keep one on my bench at all times. Write down three numbers:

Outer diameter (OD) – the width of the hole or the outer edge of the part.
Inner diameter (ID) – the size of the shaft or bolt that will go through the spacer.
Height (H) – the exact distance you need to keep between the two parts.

Add a Little Play

Unless you’re machining a metal part with a CNC, give yourself a tiny clearance of about 0.1 mm on the ID and OD. This prevents the spacer from binding.

Decide on the Feature Set

Do you need a hole for a bolt, a slot for a wire, or a raised lip to hold a washer? Sketch these features on paper or in a simple CAD program like Fusion 360. Keep the design as simple as possible – every extra cut adds time and risk.

Export and Check

If you’re 3D printing, export the model as an STL file and run it through a slicer. Look at the layer height and wall thickness; I usually set a wall of at least two perimeters and a layer height of 0.15 mm for a smooth finish.

Tools You’ll Need

Digital caliper – for accurate measurements.
Drill press or hand drill – to make clean holes if you’re machining metal.
Tap set – only if you need internal threads.
3D printer – any FDM printer will do for plastic spacers.
Deburring tool or file – to clean up sharp edges.
Thread locker (optional) – to keep screws from loosening.

Step‑by‑Step Installation

1. Prep the Surfaces

Clean the mating surfaces with a lint‑free cloth. Any dust or oil will cause the spacer to sit unevenly.

2. Test Fit the Spacer

Place the spacer in the gap without any fasteners. It should sit flush on both sides. If it’s tight, sand a little off the edges. If it’s loose, add a thin shim or re‑print a slightly larger version.

3. Align the Holes

Insert a bolt or screw through the spacer and the two parts. Rotate it a few turns to make sure the threads line up. If you feel resistance, you may have mis‑aligned the holes – back the bolt out and double‑check the drill size.

4. Secure the Fastener

Apply a dab of thread locker if the joint will see vibration. Tighten the bolt to the recommended torque (usually printed on the bolt head or in the hardware spec). Use a torque wrench if you have one; a good rule of thumb for small bolts is 0.5 Nm per millimeter of bolt diameter.

5. Verify the Gap

After tightening, re‑measure the gap with the caliper. It should match the height you designed for, within 0.1 mm. If it’s off, loosen the bolt, adjust the spacer, and try again.

Testing and Tweaking

Give the assembly a gentle shake. If you hear any rattling, the spacer may be too short or the fastener not tight enough. For high‑vibration setups, consider adding a rubber washer on one side of the spacer to dampen movement.

I once built a small camera mount for a drone using 3D‑printed nylon spacers. The first version was a hair too short, causing the camera to wobble during flight. A quick re‑print with a 0.2 mm taller spacer solved the problem and saved the project from a costly redesign.

When to Go Custom vs. Off‑the‑Shelf

If the gap is a standard size (like 5 mm or 10 mm) and the load is low, you can often buy a ready‑made spacer from a hardware store. But as soon as you need a non‑standard diameter, a special feature like a slot, or a material that matches the rest of the build, custom is the way to go. It may take a little extra time, but the reliability you gain is worth it.

At Spacer Solutions we’ve seen countless builds that fell apart because the maker tried to force a generic part into a precise spot. A little planning, a few measurements, and a custom spacer can turn that same project into a sturdy, long‑lasting piece of hardware.

So next time you’re staring at a tiny gap that just won’t close, remember: a well‑designed spacer is your secret weapon. Grab your caliper, sketch a simple shape, and let the material you choose do the heavy lifting. Happy building!