Clamshell, split along the length
- Common on power tools, where the housing is also the grip
- Motor, switch, and wiring drop in from the side before the halves close
- Each bearing seat is shared between two parts, so both halves must match closely
Molded part guide: motor housings
Injection Molded Motor Housings
A molded motor housing holds the stator still, keeps the rotor running true between two bearings, and gets rid of the heat the motor makes. On a power tool it is also the handle.
The job
Two bearings, one shaft, and a lot of heat
Most motor housing problems come back to bearing alignment or temperature.
The rotor shaft runs in two bearings, usually one at each end of the housing. If those two seats are not on the same axis, the bearings load up, the motor gets noisy, and it runs hotter than it should. With a molded housing, alignment depends on how the two seats are split between parts and between halves of the tool.
Plastic grows more with heat than a steel bearing does, and it relaxes under a press fit over time. A bearing that is snug when cold can loosen once the motor has spent enough time running hot. That is why many molded housings carry a metal sleeve or insert at the bearing seat instead of a plain plastic bore.
Glass-filled nylon is the usual starting point for power tool and appliance motor housings because it is stiff, tough, and handles heat well. Glass-filled PBT and PPS come in where moisture pickup or higher temperatures rule nylon out.
Bearing seats
Three ways to seat a bearing in a molded housing
Each trades cost against how well the fit holds up over the life of the motor.
- Pressed into a molded bore. Lowest cost, suits small, cool running motors where some fit relaxation is acceptable
- Pressed into an insert molded metal sleeve. The plastic holds the sleeve, the steel holds the bearing fit
- Bearing or bushing insert molded directly. No pressing step, but seat alignment is fixed by the tool with no adjustment afterward
- Where both seats can be formed in the same part and the same side of the tool, alignment is easiest to hold
Heat
Getting heat out of a plastic motor housing
Plastic insulates, so heat has to leave by a route you design in.
| Route | How it works | Housing impact |
|---|---|---|
| Fan and airflow | A fan on the shaft pulls air through intake and exhaust slots | Slot pattern, finger guarding, and keeping intake away from the user's hand |
| Metal heat path | An aluminum or steel part carries heat from the stator to the outside | Insert molded or assembled metal, with the plastic built around it |
| Stator encapsulation | The stator is overmolded in a resin that conducts heat but not electricity | Fewer parts and better heat transfer, but the stator becomes a molding insert |
| Sealed, no airflow | Heat leaves only through the housing wall and mounting | Resin must handle the full running temperature, which often points to PPS or PBT |
Where to split
Clamshell halves or a cup with an end bell
The split decides which part carries the stator and how the bearings line up.
Cup and end bell, split across the axis
- The stator bore and one bearing seat sit in one part, which helps alignment
- The end bell locates on a spigot so the second seat stays centered
- Common on appliance, pump, and fan motors
Drawing
What to send with a motor housing
The motor data matters as much as the housing model.
Bearing part numbers and the fit you want on each seat
How the stator is held: pressed, bonded, clamped, or encapsulated
Running temperature at the housing, and whether the motor is fan cooled
Any metal sleeves, heat paths, or threaded inserts to be molded in
Grip areas that need a soft overmold, on hand-held products
Flame rating the product needs, so the resin grade can be matched
Keep reading
Related guides
Materials and methods behind a molded motor housing.
Glass-filled nylon
The default for tool and appliance housings.
Glass-filled nylonPPS
For sealed, hot running motors.
PPSInsert molding
Metal sleeves and heat paths molded in.
Insert moldingOvermolding
Soft grips on tool housings.
OvermoldingTolerance stack up
Adding up errors between two bearing seats.
Tolerance stack upNylon 6 vs nylon 66
Heat and moisture differences between the two.
Nylon 6 vs nylon 66Gears
The gear train that often shares the housing.
GearsPump housings
When the motor drives a wet end.
Pump housingsMolded parts hub
Every part-type guide, grouped by family.
Molded parts hubDrone frames
Frames that carry the motor mounts.
Drone framesFAQ
Questions about molded motor housings
Can the bearing seats be machined after molding?
Yes, as a secondary operation. Some programs mold the seats slightly undersize and finish them to size, which takes molding variation out of the alignment. It adds a step, so it is usually kept for motors where alignment is critical.
Can you overmold our stator?
We can review it. The stator becomes an insert that has to be located and held in the tool, and the resin has to suit your insulation and heat requirements. Send the stator drawing with the housing CAD.
Why is our motor noisier in the molded housing than in the prototype?
Common causes are bearing seats that shifted as the part cooled, a bearing fit that has relaxed, or thin walls that resonate. Measuring both seats on molded samples is the place to start.
Who owns the tooling?
You do. The customer owns the tool.
Next step
Quote the housing and end bell together
Upload the housing CAD with bearing and stator details. DFM feedback covers seat alignment, insert placement, and thick sections around the motor.