Q2
3D Printing Tip: Easily Turn Models into Keychains
Struggling to hang your favorite 3D prints? Learn to add a perfect hole to any model in just a few clicks with QIDI Studio. Transform your prints into keychains!
For a standard split-ring keychain, model the hole at about 4 mm in diameter with at least 2 mm of solid material around it. Both turns of the ring's wire have to sit inside the hole, so a 1.2 mm wire ring needs 2.4 mm of clearance before you add any working room. In QIDI Studio you add that hole in two clicks with a negative part.
Every so often I find a model I love and want to hang it off my keys, and it has no hole. Adding one is genuinely a two-minute job in the slicer — no CAD, no remodelling. The part that takes longer to learn is what size to make it, so that is where this starts.
How big should a keychain hole be?
The size is set by what goes through it, not by the size of the model. Work it out like this:
Hole diameter = (number of strands passing through × strand thickness) + about 1 mm of clearance.
A split ring is the case that surprises people. It is a doubled loop, so once it is seated, two turns of wire occupy the hole, not one. A ring made from 1.2 mm wire therefore needs at least 2.4 mm before clearance, which is why 3 mm holes feel so tight and 4 mm ones just work.
| Attachment | What sits in the hole | Suggested modelled diameter |
|---|---|---|
| Standard split ring (about 1.0–1.2 mm wire) | Two turns of wire | 4 mm |
| Heavy split ring (about 1.4–1.6 mm wire) | Two turns of wire | 5 mm |
| Ball chain, standard dog-tag size (2.4 mm balls) | One ball | 3.5 mm |
| Lobster clasp or trigger snap | The closed hook | 4–6 mm, measured on the hook |
| Small carabiner | The bar stock | 2 × stock diameter + 1 mm |
| Paracord (about 4 mm), doubled through | Two strands of cord | 9–10 mm |
| Flat lanyard clip | Folded webbing | 8 mm or a slot rather than a round hole |
Two corrections to apply to whatever number the table gives you.
Small holes print undersize. An FDM printer approximates a circle with straight segments and the extrusion pushes slightly inward, so a 4 mm hole typically measures a little under 4 mm on the part. Model it 0.2 mm larger as a starting compensation, or use the X-Y hole compensation field in QIDI Studio's Quality → Precision settings so every hole in the print is corrected at once. Then measure a real part with calipers rather than guessing again — our tolerances guide covers how to find your printer's actual offset.
Leave enough material around it. A hole 0.5 mm from the edge is a tear waiting to happen. Keep at least 2 mm of solid plastic on every side of the hole, and 3 mm if the model is going on a real keyring that gets dropped, sat on and yanked out of pockets.
Schematic Diagram
Original Model:
Modified Charm Version:
Operation Guide
There are two simple ways to add a hanging hole in QIDI Studio: adding a part, and adding a negative part. Which one you want depends on whether there is anywhere on the model to put a hole in the first place.
| Method | What it does | Use it when |
|---|---|---|
| Add a part (torus) | Adds a ring of solid material fused to the model | The model has no spare thickness — you are building a new tab to hang it from |
| Add a negative part | Subtracts a cylinder or torus from the model | The model already has a thick area, such as a hat, base or slab, to put a hole through |
1. Using parts
After importing the model file, right-click on the model and select Add Part → Torus.
Use the move, rotate and scale tools to set the torus's position, angle and size until it forms a suitable hanging hole. You can also give it its own colour.
Two things to check before you slice. Make sure the torus overlaps the model rather than merely touching it — a 1 mm intersection gives the two bodies a real bonded cross-section instead of a contact seam that snaps off. And check the torus's inner diameter against the table above, because scaling the torus scales the hole with it.
2. Using negative parts
Right-click on the model and select Add Negative Part, then choose a cylinder or torus as needed. A negative part is a shape that gets subtracted from the model instead of added to it — the same idea covered in our guide to negative parts in QIDI Studio.
Adjust the size and position of the negative part. Set the cylinder's diameter to the figure from the table, and make it longer than the model is thick so it punches all the way through — a negative part that stops short leaves a blind pocket, which looks identical in the 3D view and only shows up in the slice preview.
Click Slice, and you will see a through-hole formed at the location of the negative part.
Once confirmed, send the file to the printer and start printing.
Print settings that decide whether the tab survives
A keychain is a small part that spends its life being pulled on. Three settings matter more than the rest.
| Setting | Suggested value | Why |
|---|---|---|
| Orientation | Lay the tab flat on the plate | FDM parts are weakest between layers. Flat on the plate, the pull runs within a layer instead of trying to peel two apart |
| Wall loops | 4 or more | Around a small hole the walls are the part; infill barely contributes |
| Infill | 30–50% or higher on a thin tab | A hole punched over sparse infill has almost nothing holding it |
Material matters too. PLA is the easiest thing to print, but it starts softening around 60 °C, and the inside of a parked car in summer can reach that. For keys that live in a pocket, a bag or a vehicle, PETG or ASA from the filament range holds up far better. If you want the charm in more than one colour, the colour painting tools and a QIDI BOX handle that in the same project.
FAQ
How big is a keychain hole?
Most 3D printed keychains use a hole of about 4 mm, which clears the two turns of wire in a standard split ring with room to move. Thicker rings and carabiners need 5 mm or more; a ball chain needs only about 3.5 mm.
What is the minimum hole size for a keyring?
Twice the wire thickness of the ring, since both turns of a split ring sit in the hole at once. For a 1.2 mm wire ring that is 2.4 mm as an absolute floor — but at that size the ring binds and the hole is hard to thread, so 4 mm is the practical minimum.
Why did my keychain hole print smaller than I modelled it?
FDM holes almost always come out slightly undersize, because the circle is approximated by straight segments and the extrusion is pressed inward. Model the hole about 0.2 mm larger, or set X-Y hole compensation in the slicer's precision settings, then verify with calipers on a real print.
How thick should the material around the hole be?
At least 2 mm on every side, and 3 mm for a keychain that will carry actual keys. Combine that with four or more wall loops so the ring around the hole is solid perimeter rather than infill.
Can I add a keychain hole without CAD software?
Yes. Adding a negative part in QIDI Studio subtracts a cylinder from the model without touching the original file, so you never open a modelling program. The change lives in the project and can be undone at any time.
Which filament is best for a keychain?
PETG and ASA are the practical choices — both stay rigid at the temperatures a pocket or a car interior reaches, and both are tougher than PLA under repeated pulling. PLA is fine for a display piece or a bag charm that stays indoors.
Conclusion
Two clicks add the hole; the size is what makes it usable. Work from what goes through it, add a millimetre of clearance, compensate for FDM's habit of printing holes small, and keep 2 mm of material around the edge. One of the real pleasures of 3D printing is that a free download or a purchased design can be adapted to what you actually need — and slicer-side edits like this need no modelling skill at all. QIDI Studio is free and open source; the code is public in the QIDI Studio repository, and every machine in the QIDI lineup uses it. For more small-print ideas, see our beginner project list, and the background on keychain hardware is a quick way to see what else you can hang a print from.
