UPDATE (4/6/2024): I uploaded/replaced InnerDial.stl with one that has a slightly smaller diameter. The original worked great for me, but I discovered that my printer was printing it at about .3mm smaller diameter. The adjusted InnerDial should be more forgiving. (if anyone does print this, any feedback on success/failure is appreciated)
 
This is my take on a Combination Lock Box. The inspiration for this was wanting to provide a personal/fun touch when giving money or gift cards for birthday gifts and such. The lock box works by needing to rotate each of the four dials to have the proper symbol aligned at the top, to unlock. What dials are used and combination can be personalized. For an added personal touch, can include a top handle of choice as well.
I've included several choices for dials and handles, so only print what you want for your box.
OR, make your own. I've included STEP and Fusion 360 files for creating own custom dials and handles. My hope is others will be inspired to post and share more dials and handles.

Read below for instructions/guide on what to print, or watch this video for a complete overview:
3D Print Personal Combo Box Assembly

Print settings: No Supports or Extra Parts needed, and Glue Optional. I print every part using .2 layer height with 8% cubic infill. All my prints were done with PLA of various types, brands, colors. There are some precision aspects to this, so printer should be pretty well dialed in.

Here is a tutorial video I threw together for creating own custom handles and dials:
3D Print Personalized Combination Box - Dial/Handle tutorial

Core Parts

The following are base parts that all lock boxes will need:
MainBox (x1) - This is the core box and is the largest part to be printed
InnerDial (x4) - This dial will be 'internal' and are a core part of the locking mechanism, need 4 of these.
LowerLockDisc (x8) - The lower lock discs are also internal part of the locking mechanism, need 8 of these (don't worry these are small)

Core Assembly

First set the MainBox on its side so one of the sides is facing upwards. Insert two LowerLockDisc through the square 'access' slots in the side of the Main Box (Note these discs will be loose until the Inner Dial is put in). With the Box still positioned on its side, slide one of the Inner Dials into the slot, position it so it's center hole aligns with the Box side hole. Once this inner dial is in place, you can freely rotate the box, as the lock discs will be secure in place. Repeat this same thing for each of the other 3 sides. NOTE: When inserting the inner dial, you don't need to worry about which way it's facing. I do like to insert it such that the rounded part of the inner hole is facing up, just to make inserting the couplers later a little easier.

Outer Dials

Dialnn_desc (x4) - What outer dials you print will be based on personal preference. Note the dials come in 3 flavors of 8, 10, or 12 choices.
DialCouplernn (x4) - Each dial needs an accompanying DialCoupler (e.g. an 8 choice dial would use the DialCoupler08, and so on).
The reason for the 3 connector types, is because need to be able to align any choice on the dials.

Two Color Printing: Dials have raised 'etching', to do two color printing, set filament change at layer 22 (assuming .2 layer height)

The Dial08_EmojiFace dial can be printed with 3 colors to great effect. For this, set change at layer 22 and again at layer 24.

Outer Dial Assembly

First need to insert a DialCoupler, from the inside of box, through the InnerDial (this can be the most fiddly part of the whole assembly). Note: the coupler will only go through the inner dial one way. Look for where the rounded part of the InnerDial hole is positioned, and align the coupler to match. The coupler has arrows on both sides that point to the 'top' (or rounded position). This connection is designed to be a tight fit, a decent amount of force may be needed. (The first time, it may be good to test out this fit outside the box, just to get a sense of how coupler sets into the inner dial).

Once the coupler is in place, then take the appropriate outer dial and position the desired 'combination value' to align with the arrow on the coupler. The dial will be in an unlocked position when the arrows on the coupler are pointing straight up, this is the guide for setting the outer dial to the desired value. Once positioned, press the coupler and outer dial together, the fit is designed to be tight, and press fit may be good enough. Initially I do not advise super gluing the dials until everything is set, can always "pop" the outer dial off later and apply super glue if wanting to ensure outer dials don't come off from coupler.

TIP: Initially the dials may "stick" or turn somewhat difficult. Perform some spins with the dials to loosen things up. My experience is that without supports, the holes in the box can have some "rough" elements, which just rotating the dials can smooth out. The dials should spin pretty easily, but still with some friction.

Cover

I've designed this lock box to support two flavors of locking:
Single Stage = This mode is simplest and only requires printing one of the 1Stage covers. This approach is probably good enough for most cases.
Two Stage = This mode has several parts to print, but provides a mode that is very difficult to guess by feel.

The core box and dials support either locking mode, so can switch modes later if desired. I recommend using the single stage cover if the lock box is going to be for younger audience.

There are two types of covers for each stage, one with a slot in top (think piggy bank) and one without. So if wanting the lock box to double as a piggy bank, choose WithSlot cover.

Single Stage Lock:
Cover1Stage_ (x1): print either the WithSlot or NoSlot cover and that's it.

2 Stage Lock:
Cover2Stage_ (x1): print either the WithSlot or NoSlot version.
UpperLockingDisc2Stage (x4): These are part of a "second" locking mechanism, print 4.
LockBar2Stage (x1): This is part of the internal locking mechanism, print 1.
LockChannelCover2Stage (x4): these secure the lock bar and keep lock channel from obstructions (need at least one, but recommend 4)

Cover Assembly

Set all four dials to unlocked position
If going with the single stage route, then simply, slide the cover onto the box, and scramble the dials.

For 2 stage lock:
First set the LockBar into the slot made by the outer and inner wall of the MainBox (feet first). With all four dials set to unlocked position, the LockBar will be able to "settle" down. Now insert the 4 upper locking discs into the 4 upper corners of the lock box. They should easily 'pop' into place with things being in an unlocked state.

Before going further, this is a good time to test things out (without the cover on). The lock bar should slide up and down freely when tipping the box upside down. Make sure to hold your fingers over the top slot so Lock bar doesn't completely fall out. With the box tipped upside down, turn one of the dials to a locked position, now tip the box upright and the lock bar should be sitting up on the lower lock disc. Turning the 'locked' dial to unlock position should cause the lock bar to fall (by gravity). The key is that each lower and upper lock disc moves freely in its channel and the lock bar also slides up and down on its own. If there is any rough edges or print artifacts on the lockbar, could cause enough friction to prevent it from naturally sliding down when unlocked. Once feel good about the lockbar behavior, can try with the cover on. NOTE: when in an unlocked position, the dials will not turn freely, as the lock bar will be blocking. To lock, insert cover, then tip box so that the lock bar slides towards the cover, then turn dials to lock.

Try things out, for a bit, and once know things are working. Can add the LockChannelCover2Stage to each corner of the main box. Set the ChannelCover top first, so it sits flush with the inner wall, then snap the bottom in place to the bottom of the lock channel. The Channel Cover not only ensures that the lock bar stays in place when the main cover is off, but also prevents any contents of the box from blocking the lock channel.

Handle

Handle Assembly