Voron Heat-Set Insert Guide — Proper Insertion, Sizes, and Common Mistakes

Build Reference Hardware

Heat-set inserts (also called threaded inserts or brass inserts) are the standard fastening method for Voron printed parts. They provide strong, reusable threads in plastic that withstand repeated screw insertions far better than self-tapping screws. However, improper insertion is one of the most common mistakes in Voron builds — melting the plastic too much, inserting at an angle, choosing the wrong insert size, or using too much force. This guide covers everything you need to know: insert sizes (M3, M4, M5), soldering iron vs press-fit methods, correct insertion depth and alignment, sourcing quality inserts, and how to fix common failures. Last updated: May 2025.

Heat-Set Insert Sizes for Voron

The Voron design uses three standard insert sizes. Each has a specific printed hole diameter and depth requirement:

Always verify the actual outer diameter of your inserts against the Voron printed part STL. Insert dimensions vary between manufacturers. If your insert OD measures 4.8mm, the printed hole needs a 4.8mm diameter — not the nominal 4.5mm. Measure with calipers, do not rely on advertised specs.

Knurled vs Diamond-Knurl vs Helical Inserts

• Knurled (Straight Knurl): Parallel ridges along the insert body. Most common in Voron kits. Suitable for ABS and ASA with proper hole sizing. Rocking the soldering iron helps them bite.
• Diamond-Knurl: Cross-hatch pattern provides superior grip in the plastic. Preferred for high-torque applications like extruder mounts and bed mounts. Slightly harder to insert but less likely to spin.
• Helical / Spiral: Thread-like ridges that screw into the plastic. Best insertion quality with minimal plastic displacement. Common in McMaster-Carr and high-end insert brands.
• Solid-body (Smooth): No knurling. Used with ultrasonic insertion or press-fit only. Not recommended for soldering iron insertion.

Insertion Methods

Soldering Iron Method (Recommended)

The soldering iron method is the most common and reliable technique for Voron builds. It gives you direct control over insertion depth, alignment, and temperature.

• Iron type: Adjustable temperature soldering iron (TS100, Pinecil, or any Hakko-compatible station). Fixed-temperature irons (15W or 25W) are too weak — the insert will cool the tip and stall insertion.
• Tip: Use a dedicated insert tip (cone or flat-tipped with a small recess to hold the insert). Alternatively, use a 1.5mm flat-blade screwdriver tip that fits inside the M3/M4 thread bore. A standard conical tip also works — fit it into the thread and transfer heat through the insert body.
• Temperature: 240-280C for ABS/ASA, 220-250C for PLA/PETG. Too hot (>300C) melts the plastic excessively and weakens the surrounding part. Too cold (<200C) causes the insert to drag and not seat fully.
• Technique:
  1. Set iron to 260C and let it stabilize.
  2. Place the insert on the tip magnetically or by friction-fitting it into the tip's recess.
  3. Position the insert over the printed hole. Apply gentle downward pressure — do not force.
  4. The insert will melt its way into the plastic. Push until the flange (if present) is flush with the surface, or the insertion depth mark is reached.
  5. Hold for 3-5 seconds after reaching full depth, then remove the iron. Let the plastic cool for 10-15 seconds before releasing the part or handling the insert.
  6. Optional: Apply a small amount of downward pressure with a screwdriver while the plastic is still warm to ensure the insert is fully seated.

Press-Fit Method

Press-fitting (also called cold insertion) uses force instead of heat to drive the insert into an undersized hole. This method is faster but riskier and not recommended for Voron builds.

• Hole sizing: The printed hole must be 0.2-0.3mm smaller than the insert OD. A 5.0mm OD insert needs a 4.7-4.8mm hole for press-fit. Printing a test hole calibration block is essential.
• Tool: Use a vise or arbor press with a flat punch. Do not hammer — impact force cracks the plastic around the insert.
• Support: Place a sacrificial part or scrap ABS underneath the hole being pressed to support the back side. Without support, the print will bulge or crack.
• Pros: No soldering iron needed, no heat damage to surrounding plastic, faster for high-volume insert placement.
• Cons: Hole sizing is critical and forgiving of only ~0.1mm tolerance. PLA parts are brittle and may crack under press-fit force. The insert has less pull-out strength compared to heat-inserted knurled inserts.

Ultrasonic Insertion

Ultrasonic insertion uses high-frequency vibration to melt the plastic around the insert. This is the industrial standard but requires specialized equipment ($500+). Not practical for most Voron builders.

Insertion Depth and Flush vs Recessed

Most Voron printed parts are designed for the insert to sit flush with the surface. The STLs include a counterbore or a flat-bottomed hole that acts as a depth stop.

• Flush inserts: The top of the insert is exactly level with the surface of the printed part. This is the standard for Voron panel mounts, frame brackets, and electronics mounts.
• Recessed inserts: The insert sits below the surface by 0.5-2.0mm. Used where a screw head needs to be flush with the part surface (e.g., Voron bed mounts, gantry joints).
• Over-insertion: Pushing the insert too deep creates a bulge on the back side of the print. This bulge can interfere with panel fit or electronics clearance. Check the back side of the hole before and after insertion.
• Under-insertion: The insert sits above the surface. This prevents the mating part from sitting flush and may crack the print when the screw is tightened. Reheat and push the insert deeper if this happens.

Common Mistakes and How to Avoid Them

Mistake #1: Wrong Hole Size (Too Small)

If the printed hole is too small, the insert will displace too much plastic, causing bulging, cracking, or incomplete seating. Fix: Measure your insert OD with calipers. Drill out the hole to the correct size using a drill bit 0.1-0.2mm smaller than the insert OD. For ABS, you can run the soldering iron bit through the hole to ream it gently.

Mistake #2: Wrong Hole Size (Too Large)

A hole that is too large results in a loose insert that spins when a screw is inserted. Fix: The only reliable fix is to print the part again with corrected hole dimensions. As a temporary workaround, apply a drop of superglue or epoxy around the insert before heating — this is not a permanent solution and will fail under torque.

Mistake #3: Insert Inserted at an Angle

Angled inserts cause screws to cross-thread and place uneven stress on the plastic. Fix: Use a soldering iron with a stand that holds the iron vertically. Alternatively, create a simple guide block with a vertical hole that fits the soldering iron tip to keep it perpendicular. If the insert is already crooked, heat it up (260C), use a screwdriver to straighten the insert while the plastic is molten, and hold it steady until it cools.

Mistake #4: Too Much or Too Little Heat

Overheating (>300C) degrades the ABS polymer around the insert, creating a brittle zone that cracks under load. Underheating (<200C) prevents the insert from fully seating. Fix: Use a calibrated soldering iron. Set to 250-270C for ABS/ASA. Test on a scrap part first to confirm the temperature is right.

Mistake #5: Insert Spinning in Place

A spinning insert cannot hold a screw securely. This usually happens because the hole was too large, the insert was not hot enough, or the knurling pattern was unsuitable. Fix: Remove the spinning insert by heating it and pulling it out with pliers. Print a replacement part with corrected hole dimensions. For M3 inserts, sometimes reaming the hole slightly and using an M4 insert (if the part has enough wall thickness) can salvage the part.

Mistake #6: Plastic Gobbing into the Thread

Molten plastic can flow into the internal threads of the insert, making it impossible to start a screw. Fix: Clean the threads immediately with a tap of the same size (M3 tap for M3 insert) or chase the threads with a screw. Prevent by using inserts with a closed top or by placing a small amount of thermal paste or a small screw inside the insert during insertion to block the plastic.

Recommended Insert Sources for Voron Builds

• McMaster-Carr: The gold standard. McMaster's press-fit and heat-inserts have precise dimensions and consistent knurling. High cost but zero variability. Part numbers: 94180A331 (M3 x 5mm knurled), 94180A335 (M4 x 6mm), 94180A339 (M5 x 8mm).
• Amazon (common brands): "Boltun" and "Gikfun" brand inserts are popular with Voron builders. Quality varies — always measure with calipers before using. Good for practice and spare parts.
• AliExpress / Voron kit suppliers: Most Voron kits include a bag of assorted M3/M4/M5 inserts. Quality is acceptable for most applications. If an insert feels loose or has poor knurling, discard it and use a known-good replacement.
• Fabreeko / West3D: Carry premium inserts specifically for Voron builds. Diamond-knurl and helical style inserts available. Slightly more expensive but guaranteed to match Voron printed part hole dimensions.

Tools for Heat-Set Insertion

• Soldering iron: TS100, Pinecil V2, or Hakko FX-888D. Adjustable temperature is mandatory.
• Insert tips: Dedicated insert tips (conical with a flat face, sometimes magnetized). A 1.5mm flat-blade tip also works well for M3 inserts.
• Calipers: Digital calipers to measure insert OD and verify hole dimensions in your printed parts.
• M3/M4/M5 tap: For cleaning plastic out of insert threads. A tap handle makes this easier.
• Heat sink pliers / cross-locking tweezers: To hold and position hot inserts safely. Magnetic tweezers also work for picking up small inserts.

Master heat-set insert technique early in your Voron build. It is a skill that takes less than an hour to learn and the difference between a professional-quality build and a frustrating one. When in doubt, insert a test piece into a scrap print before working on your actual Voron parts.

Happy building!