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Hinged Chest with Working Lock and Wood Texture

3D printable toy treasure chest with a simple functional lock (formerly thing:2803507)

License

Creative Commons - Attribution - Share Alike

Attribution

This is a remix of athey's Small Hinged Treasure Chest (Thingiverse thing:27635), using the wood texture from devonjones' OpenForge Wooden Floors (Thingiverse thing:1585586)

Gallery

Photo 1🔎 Photo 2🔎 Photo 3🔎 Photo 4🔎

Description and Instructions

My godson has some kind of obsession with collecting small things in small chests, and he wanted a chest with a working lock. So, for his next birthday I took athey's Small Hinged Treasure Chest and designed a lock mechanism for it. Of course it is the most basic lock possible with only one possible key and picking it with a bent paperclip is trivial, but it is functional. I also spiffed up the overall looks of the chest with extra details like the excellent wood texture from the OpenForge Wooden Floors by devonjones. The hinge has been made slightly beefier to reduce the risk of it breaking.

To unlock the chest, rotate the key counter-clockwise and open the lid while keeping the key turned. The lock cannot be left in the open position, closing the chest automatically locks it. This video demonstrates how the chest works.

I made four different key designs. The skull and heart keys will probably be the most popular with little (and big) children by far :)

Assembly is rather straightforward but the parts must be printed and mounted accurately for the lock to neither fail to close, nor be sloppy. See the images for instructions. On a well-calibrated printer the parts should only require minimal post-processing to make them fit. If your prints tend to be sloppy, some extra sanding and scraping may be required. See the post-printing section for more details.

The dimensions are 76 × 46 × 57 mm for the bulk of the chest, and 76 × 51 × 58 mm with the hinges and details included. It should be possible to scale up the model slightly, but you may need to scale up the latches a tiny bit more in two of the three dimensions to keep them a tight fit.

If you want to print the chest at 200% size, print the models from the Scaled200Pct subfolder with Size200 prefix. These are already upscaled to 200% (meaning about 152 × 102 × 116 mm), and have been modified with reduced wall thickness and appropriate tolerances for the size. I haven't printed this larger model so I cannot guarantee it will work perfectly. Feedback is welcome!

This print is not recommended for beginners. Print some other things first, especially overhang and bridging tests, and make sure they are OK before you start with this.

Printing

Do not print everything together unless you have experience and know your 3D printer well. The lock parts and keys are best printed with different settings anyhow, but printing the chest and lid together means taking unnecessary risks. This goes for any print, sequential printing is almost always the better strategy.

The chest in the photos was printed in rigid.ink ‘Pearl Red’ ABS. For the chest and lid, I used 0.2 mm layers with 20% infill, with a brim to avoid warping.
The latches and keys were printed with 0.1 mm layers and 3 perimeters. It is important to print these parts with thin layers, to ensure they have an accurate thickness. You should also print them slowly to ensure the latches have an accurate shape. If you print in PETG and the lock parts are too flexible, try printing those parts in PLA or ABS instead.

Supports should not be needed for the regular size model, especially not if you print the ‘easier’ variant of the lid that has extra structures to help with bridging. The dome of the lid has overhangs that go beyond 45°, but those overhangs are actually printed as bridges, therefore if your printer passes the bridge torture test, in theory you do not need supports. In practice, filaments that tend to warp and curl can cause problems and lead to a failed print, therefore I do recommend to print the easier edition of the lid. You'll only lose a marginal amount of inside space compared to the other model.

For the 200% model, supports may be required for the lid, although a well-behaved printer should still be able to print the ‘easier’ model without supports. You may need to experiment with the number of perimeters and infill for the ‘Size200-Latch_lower’ part to end up with something that is not too rigid.

The hinges are the most fragile parts. If you plan to give this to a child or use it for more than merely decoration, I advise to ensure the zones around the hinges are printed with 3 or even 4 perimeters. You don't need to print the entire chest with that many perimeters: modern slicing programs like PrusaSlicer allow to increase the number of perimeters in specific zones by means of ‘modifiers.’ This saves on material and print time, because 2 perimeters are sufficient for the bulk of the chest and lid.

Perimeters example in PrusaSlicer🔎

Troubleshooting

I'll repeat: do not try to “save time” by shoving everything on the print bed and doing one lengthy print. This is a bad idea in general because if anything goes wrong (a power cut, you run out of filament, the extruder crashes on something warping, …), the whole print is ruined. Also, your printer will waste more time on travel moves, and print quality risks being worse due to stringing and oozing.

If you see the print failing due to your printer suddenly shifting position when it reaches the top of the lid, it means:

  • The print is warping excessively. Try the ‘easier’ model with a higher cooling fan speed. If this doesn't help, use supports.
  • Your stepper drivers are really weak which causes them to skip when the extruder bumps into obstacles. You will have problems with other models as well. Try increasing the stepper drive current if possible—if you cannot, well then you probably know why your printer was so cheap.

Post-printing

Make sure to remove any traces of a ‘squashed’ first layer (elephant's foot syndrome) on the latches and hole in the lid, through sanding or scraping with a knife. Try hooking the latches into each other with your hands: they shouldn't easily slip out of each other. If they get unhooked easily, try to adjust the hook shape with a knife.

If the latches are too thick to fit in the slots, sandpaper is your friend. You could also try printing them again with reduced X and/or Z dimension scaling, but sanding or scraping with a blade is much easier.

Assembly

The lower latch (long piece) must be mounted in the chest with the hook pointing to the right, and the top perfectly flush with the edge (simply pushing it in on a flat table should do the trick). If you cannot push it deep enough, scrape off some material from the bottom end.
The latch in the lid must have its hook pointing to the left, and ideally the edges of the square part should be flush with the bottom edge of the lid. If the lock doesn't catch, you either need to pull this latch out again by a fraction of a millimeter, or shave off a bit of material from the inside of the hook with an X-acto knife.

Assembly 1🔎 Assembly 2🔎

If the lid doesn't close easily due to the latch bumping against the top edge of the chest, try sanding or scraping a bit of material from the front edge of the latch.

When printed accurately, the parts of the regular size model should fit tightly enough that no glue is required. The advantage of not using glue is that the latches will pop out of their sockets if the chest is pulled open with excessive force, instead of breaking and leaving bits behind that are impossible to repair. In other words, you need to make a choice between a chest that is harder to open without a key but will be broken if someone does manage to open it; or a chest that is easier to open but can be repaired if needed. After all this is just a toy, not a secure storage device!

If you do want to use glue, do not use cyanoacrylate (super glue) unless you are skilled in using it. It tends to solidify in a fraction of a second, causing the parts to become stuck before they can be inserted deep enough, making the lock unusable. The best place to apply glue with minimal risk of the latch becoming stuck, is shown in the following image. You could also try to use strips of adhesive tape to get a tighter but non-permanent fit.

Glueing

Updates

2018/07/25

Improved tolerances on the latch parts of the 200% size model.

2021/12/20

Added ‘easy’ variant of the (regular size) lid. This should reduce the risk of warping with certain filaments like PETG. Added heart-shaped key.

2021/12/26

Added ‘easy’ lid variant and heart-shaped key for the 200% size model.

Tags

box, chest, container, hinge, key, Lock, pirate, secret, toy, treasure, treasure_chest

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