Heat-Set Inserts in FDM Parts: Hole Design and Installation Checks

Start with the exact insert’s drawing, the printed material, and the intended joint. A screw’s thread size alone does not tell you the hole diameter, depth, or installation temperature. This workflow connects manufacturer guidance to a small test piece before you commit to a finished part.

Confirm the material and installation method

SPIROL distinguishes thermoplastic FDM parts from cured thermosetting SLA resin. Heat installation is applicable to thermoplastics; for thermosetting resin it recommends insert types designed for cold installation, including press-in or self-tapping inserts. This is not an instruction to cold-press a heat-set insert into resin. Do not transfer this FDM workflow to a cured resin part. SPIROL’s 3D-printed assembly guidance explains that distinction.

Record the joint before changing CAD

Use this small job card:

• Insert: maker, series, thread, length, outer geometry, and drawing revision.
• Print: exact filament, orientation, walls, infill, and profile.
• Hole: drawing requirement and measured printed diameter and depth.
• Assembly: screw length, mating part, intended loads, and acceptance checks.

This is an editorial checklist, not a manufacturer-certified design.

Check the printed hole, not only the CAD dimension

CNC Kitchen notes that printed holes can be smaller than their CAD dimensions and recommends a test specimen for the relevant material and print orientation. Its own insert instructions call for straight holes and the specified surrounding wall thickness. CNC Kitchen installation guidance.

SPIROL warns that an undersized hole can create installation stress or cracking; an oversized one can reduce retention. Match the hole shape to the insert style rather than applying one diameter or taper to every insert. SPIROL hole-design guidance.

CNC Kitchen’s March 2026 investigation distinguishes its nominal finished-hole specification from the CAD diameter needed to obtain that hole on a particular printer and material. Its observed offset and pull-out results belong to that test setup; they are not a universal CAD correction or load rating. Finished-hole versus CAD guidance.

Practical next step: print a small coupon matching the intended material, hole orientation, surrounding walls and infill. Record the actual dimensions and installation result before revising the full model. This checks fit and installation; it does not qualify the joint’s load capacity.

Leave space below the insert

For its heat/ultrasonic insert designs, SPIROL recommends a minimum hole depth of insert length plus two thread pitches and warns against the assembly screw bottoming out. Check both the insert depth and the selected screw length against the actual assembly. Treat this as SPIROL’s design guidance, not a universal substitute for another supplier’s drawing. SPIROL depth and assembly guidance.

Use the supplier’s installation procedure

For its brass inserts and installation process, CNC Kitchen describes an adjustable soldering iron set approximately 10–20 °C above the nozzle printing temperature, while noting material variation. It recommends using the iron to melt the insert in to roughly 90% of the insertion depth. Remove the iron before seating the remainder with a tool, then hold the insert until the plastic solidifies. These are instructions for CNC Kitchen’s inserts, not a generic iron setting for every insert and filament. CNC Kitchen installation process.

The iron and insert remain hot: use tools rather than fingers and follow the equipment’s handling instructions. Avoid overheating the plastic; CNC Kitchen cautions that excess heat can cause decomposition. Follow the material maker’s handling guidance. CNC Kitchen’s overheating caution.

Check the complete assembly

SPIROL identifies hole consistency, surrounding solid walls, material, and installation quality as factors in the joint’s performance. Its published test results belong to its stated specimens and conditions; they do not establish the load capacity of your part. SPIROL assembly and testing context.

Suggested acceptance record: alignment, final depth, visible damage, unobstructed screw travel, and behavior under the intended assembly requirements. A neat-looking insert alone does not demonstrate a qualified joint.

Continue through the hub

Check the PLA or PETG material reference, then the documented printing workflows. Printing profiles do not specify an insert installation temperature. For outsourced parts, use the print-farm directory and ask the provider to document insert installation and the agreed assembly checks.

Sources

These supplier documents represent two organizations. Their procedures apply to the hardware and conditions they describe.

• SPIROL: Threaded inserts for 3D-printed assemblies.
• SPIROL: Hole design for heat/ultrasonic inserts.
• CNC Kitchen: Installation and design instructions for its heat-set inserts.
• CNC Kitchen: Nominal hole dimensions versus printed CAD results.

Source guidance checked October 9, 2026. FilamentMap has not performed joint-strength testing for this guide.