Hide Phone Inside Calculator (Hollow Case Mod)
Turn a calculator shell into an openly visible phone dock by measuring the cased phone, checking the shell, and making a removable, nonconductive cradle. Leave ports and controls clear, preserve the calculator’s battery access, and never charge the phone while it is docked. This is a fit-and-access project, not a concealed compartment or certified device.
The first time I mock up a phone dock, I reach for cardboard before a saw. A phone can look as if it fits a calculator shell, then snag on a button or cover a port once it is seated. A quick mock-up reveals those problems early and helps keep the finished dock useful, stable, and easy to remove.
The aim here is an openly accessible dock: the phone remains visible and lifts out without tools. You will not modify the phone itself. Because models differ, measurements must come from your own phone and calculator rather than a universal plan.
Planning and Device Survey
A device survey checks the actual phone, case, and calculator shell before any cuts are made. No building-code rule sets dimensions for this consumer project. Product-safety principles in IEC 62368-1 concern equipment hazards, but a DIY-modified calculator is not thereby tested or certified to that standard.
Check both devices before planning
Remove the calculator’s batteries before inspecting its shell. Look for internal ribs, screw posts, the battery compartment, and any supports that keep the case rigid. If a planned change would affect the battery compartment or a structural support, do not proceed with that shell.
Measure the phone with the case you intend to use. Record its width, height, and thickness, plus the location of its buttons, ports, speakers, microphones, and cameras. Measure the calculator’s usable space and note which parts must remain untouched, including battery access.
There is no universal calculator model, cavity size, or airflow figure for this project. A measurement from another build is only a reference. Your shell and phone set the dimensions.
Decide whether the shell is suitable
Choose a shell with enough room for an open cradle and an easy path to lift the phone out. A closed cavity is not the goal. If the calculator’s shape would force you to enclose the phone, block its controls, or weaken the shell, use a different shell or stop.
- Keep the calculator’s battery door accessible.
- Avoid cutting near screw posts, ribs, and other supports.
- Plan for the phone to remain visible and removable.
- Leave the phone’s ports and controls open to access.
Next step: Make a simple sketch showing the phone’s seated position and each feature that must stay clear.
Access, Fit, and Clearances
Fit means the phone sits securely without being pinched, while access means you can reach its controls and lift it out. For a starting allowance, make the dock at least 2 mm wider on each side than the cased phone. This is a fit allowance, not a safety standard.
Measure and mock up
The phone’s case changes its outside dimensions, so do not size the cradle from the bare phone. If the cased phone measures 72 mm wide, for example, allow at least 76 mm of internal width. Apply the same 2 mm-per-side allowance to height where the cradle surrounds the phone. Recheck the actual shape; rounded corners and raised case edges can affect fit.
Use cardboard to mock up the cradle. Place the phone in it, then check whether you can reach the buttons and ports and remove the phone without bending the shell. Confirm that the cradle does not cover speakers, microphones, or cameras. A phone that fits but cannot be lifted out freely is not a successful fit.
| Check | What to do | Pass condition |
|---|---|---|
| Width and height | Measure phone with case; add at least 2 mm per side | Phone seats without being squeezed |
| Ports and buttons | Test with phone seated | Each intended feature remains reachable |
| Removal | Lift phone out by hand | No prying or shell flex is needed |
| Shell access | Check battery door and supports | Original access and supports remain intact |
These checks guide the build, but they do not replace device-specific instructions. Next step: Adjust the cardboard until the phone seats, operates, and lifts out cleanly.
Open-Dock Fabrication
An open dock supports a phone without enclosing it. A removable cradle also lets you revise the fit without permanently changing the calculator. Use nonconductive, nonabrasive support material, and keep adhesive away from the phone, battery, and heat-producing components.
Build the cradle
Transfer the mock-up. Mark the cradle’s shape and attachment points on the chosen material. Check the dimensions again against the cased phone before cutting.
Cut and smooth the support. Make the cradle from a suitable nonconductive material, such as wood or plastic. Smooth edges that may touch the phone case. Avoid exposed metal where the phone rests.
Keep the design open. Support the phone at stable contact points, but leave its ports, controls, speakers, microphones, and cameras clear. Do not add a cover or create an enclosed phone cavity.
Preserve the calculator. Keep the battery door usable and avoid modifying ribs or screw posts. If the cradle needs a cut that would weaken the shell, revise the design rather than forcing the fit.
Fit without force. Place the cradle in the shell and seat the phone. The phone should stay put during ordinary handling yet come out by hand. If it rocks, slips, or catches, adjust the support instead of pressing the phone into a tighter space.
A removable cradle can be held in place by a fitted support or another method that does not damage the shell. If you use an adhesive, follow its instructions and apply it only to appropriate shell surfaces. Do not attach anything to the phone’s battery or heat-producing parts.
Next step: Test the cradle with the calculator’s batteries still removed, then confirm that the shell and its battery access remain intact.
Safety and Functional Verification
Verification checks that the phone stays supported, remains accessible, and does not become trapped in a hot enclosure. A visible opening alone does not prove that temperatures are safe. Follow the phone maker’s charging and operating-temperature instructions; there is no universal airflow or CFM value for this setup.
Test before regular use
Check that the cradle cannot shift during ordinary handling. Confirm that the phone lifts out without force and that the dock does not press on buttons or cover openings. Recheck access to the calculator’s battery compartment and make sure the cradle has not made the shell unstable.
Do not charge the phone while docked. Charging and sustained high-load use can produce heat, and an enclosure can trap it. This design should stay open, but an opening by itself does not establish a safe temperature. If the phone warms beyond the maker’s guidance, remove it and stop using the dock.
Never cut, puncture, or load the phone’s battery. Do not use the phone as a structural part of the cradle. If the phone or its case is damaged, or the dock presses against the phone, stop and correct the fit before use.
IEC 62368-1 is a product-safety standard for information and communications technology equipment. It can inform awareness of hazards, but a home-built modification has not been evaluated or certified to it just because its principles are mentioned here.
Next step: Recheck fit, access, and temperature during ordinary use, and remove the phone if anything feels wrong.
Bench Examples: Two Fit Problems
These examples are illustrative workshop scenarios, not test results or claims about a particular calculator model. They show how measurement and mock-up can prevent common fit errors. In both cases, the phone stays visible and removable, and no charging takes place while it is docked.
A case makes the phone too wide
A builder measures a phone without its case, then finds that the cased phone catches at the cradle sides. The fix is not to force it in or sand the phone case. Measure the cased phone, add the fit allowance, and resize the mock-up before making a final cradle.
A cradle blocks a charging port
A phone seats neatly, but the support covers its port. Even if the phone is not meant to charge in the dock, the blocked opening shows that the cradle is poorly placed and may also interfere with access. Move the support and test all features again.
Takeaway: Treat a failed cardboard fit as useful information, not a reason to cut the calculator further.
Conclusion and FAQ
This project works best as a simple, open phone stand built into a calculator shell, not as a hidden compartment. Measure the cased phone, protect the calculator’s supports and battery access, and verify fit before finishing. Keep the phone accessible, and do not charge it while docked.
Can I use any calculator shell?
No. Choose a shell that can hold an open cradle without cutting its battery compartment or structural supports. If the fit requires weakening the shell, choose another model.
How much clearance should I allow?
Use at least 2 mm per side as a practical fit allowance around the cased phone. It is not a safety-standard measurement; confirm the fit with a cardboard mock-up.
Should I measure the phone with its case?
Yes. The case affects width, height, and thickness. Measure the complete phone-and-case assembly you plan to place in the dock.
Can I charge the phone in the dock?
No. Do not charge it while docked. Follow the phone maker’s charging and temperature instructions, and keep the dock open and accessible.
Does an opening make the dock safe from heat?
Not by itself. An opening does not prove a safe temperature, and there is no universal airflow figure for this design. Stop using the dock if the phone exceeds its maker’s temperature guidance.
What material should support the phone?
Use a nonconductive, nonabrasive material, such as suitable wood or plastic. Smooth contact edges and avoid exposed metal where the phone rests.
Can I glue the cradle in place?
You may use an adhesive only on suitable shell surfaces and according to its instructions. Keep it away from the phone, its battery, and heat-producing components; a removable fit is easier to revise.
Is the modified calculator certified to IEC 62368-1?
No. Mentioning that standard does not certify a DIY modification. This guide uses its safety context only; the finished project has not been evaluated to the standard.
What if the phone blocks a port or button?
Change the cradle position or shape. Do not accept a fit that blocks ports, buttons, speakers, microphones, or cameras.
Can I cut or puncture the phone battery to make it fit?
No. Never cut, puncture, or load the battery. Modify the removable cradle or select a different calculator shell instead.
(This article was written by one of our staff writers, Nathaniel Pierce. Visit our Meet the Team page.)
