An instrument housing that looks simple in a closed CAD assembly can be difficult to populate. A PCB clears the base but cannot pass its connectors through both end panels. The lid closes, yet its final screw is hidden behind the connector backshell. These are reasons to choose the enclosure split early, before detailing every cutout.
First, remove a terminology trap: “U-shaped” and “clamshell” are not universally distinct categories. Protocase’s U-shape description also uses the term clamshell. Supplier names are therefore less reliable than a section view and an assembly sequence.
This guide compares two explicitly defined concepts: a U-shaped top-and-side cover over a base, and two shallow folded shell halves meeting at a split line. It does not claim every supplier uses those names in the same way.
Sketch the opening, not only the outside shape
For the U-cover concept, identify whether the front and rear panels remain attached to the base when the cover lifts away. For the split-shell concept, identify which half carries the PCB and which carries the connectors, switches or cable restraints. Then draw the removal direction of every part.
A cover that lifts vertically needs unobstructed space above the instrument. A shell that slides off may need clearance beyond a projecting connector. A removable front plate might solve board insertion but add a separate artwork and fastening configuration. The correct answer depends on the equipment, not on the number of bends alone.
Work backward from PCB installation
Imagine a hypothetical board with a connector projecting through the rear wall and another through the front wall. Lowering the board vertically between two fixed walls may be impossible even though its final position is correct. Possible routes include a removable end panel, a separate PCB carrier installed with the board, or a housing split that leaves the relevant walls open during installation.
Do not solve that problem by enlarging both apertures without reviewing bezel coverage, connector retention and the finished appearance. Define an insertion path that respects the released component geometry. Connector part numbers and mounting drawings matter more than a simplified rectangular CAD placeholder.
Use a short sequence review before drawing release:
- Place the support hardware and board carrier in the assumed housing half.
- Install the board with its actual connector envelopes represented.
- Attach any panels that must remain loose during insertion.
- Route and restrain cables without trapping them in the seam.
- Close the cover, verify tool access and repeat the sequence in reverse for service.
This is a mechanical planning exercise, not authorization to work on powered equipment. The OEM defines isolation and service procedures for the finished instrument.
Compare the architecture against the work it must allow
| Review question | U-shaped top-and-side cover | Two shallow shell halves |
|---|---|---|
| What stays located during opening? | Often the base and its mounted assembly | Whichever half is designated as the locating structure |
| Where is the seam? | Typically along lower side edges and end interfaces | At the designed split between the two halves |
| What can block installation? | Fixed end panels, inward returns or projecting connectors | Overlapping lips, hardware and components assigned to opposite halves |
| What needs service clearance? | Cover lift or slide path plus fastener access | Opening or separation path and any cross-shell wiring |
| What must inspection reference? | Base datums and finished cover-to-base fit | Common references that control both mating shell edges |
These are review prompts, not guaranteed advantages. Either architecture can be poorly or well executed.
Put seams where the project can control them
Check whether a seam crosses a visible face, an operator-contact area, a connector opening or a specified seal path. Consider finished thickness, overlap geometry and fastener access together. A seam moved away from the display may still introduce a difficult cable path at the rear.
If electrical bonding or a sealing function is required, the responsible designer must specify the interface, materials and acceptance method. A long metal overlap does not by itself demonstrate EMC performance, and a closely fitted lip is not an established ingress rating. Keep those requirements separate from cosmetic seam acceptance.
On the drawing, state the finished condition and how the parts are restrained during checking. For a flexible shell, an arbitrary squeeze on the bench can conceal a mismatch. The approved assembly method should produce the fit being inspected.
Send the split decision with the RFQ
Include an assembly view, exploded or staged installation view, PCB and connector references, fastening sequence, desired service path and critical finished interfaces. Clarify whether the supplier delivers loose shells, a hardware-installed kit or an assembled mechanical enclosure.
Use the PCB and connector alignment guide for the dimensional chain and the rear-service clearance guide for the installed equipment envelope. DRAmetal’s custom instrument enclosures can be reviewed against the resulting drawing-defined supply scope. The key deliverable is an enclosure that can be assembled and maintained as intended, not merely a preferred shape name.
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