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 |
Service tiers
Motor housing service tiers and quote path
Housing tier for this family: Two bearing seats in line, and getting motor heat out. Upload CAD with seal path, fasteners, and heat sources called out in notes when they are not modeled.
| Tier | Environment | What matters most | Typical molded route | Quote path |
|---|---|---|---|---|
| 1 Pressed plastic bore | A small, cooler motor | The fit can loosen once the motor is hot | Glass-filled nylon | Instant quote; note the bearing |
| 2 Metal sleeve | The bearing size stays in steel | The plastic holds the sleeve | Insert molded sleeve | Upload CAD; note the sleeve |
| 3 End bell | A cup plus a separate bell | The second seat locates on a spigot | Same resin as the cup | Instant quote; send both parts |
| 4 Clamshell | A power tool, housing is the grip | Each seat is shared across two halves | Glass-filled nylon | Upload CAD; mark a soft grip if needed |
| 5 Sealed, no fan | Heat leaves through the wall | The resin has to take the running temperature | PBT or PPS | Full RFQ; note the running temperature |
Materials
Resin families: quick reference for quote notes
One primary family per shell line item. Put EMI coatings, inserts, and flame filters in comments.
| Family | Typical use on this part type | Notes for instant quote |
|---|---|---|
| Glass-filled nylon | Power tool and appliance housings | Field glass-filled nylon |
| Glass-filled PBT | When moisture rules nylon out | Field glass-filled PBT |
| PPS | Higher temperature, or a sealed housing | Field PPS |
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
Avoid these
Common design mistakes on motor housings
Two choices that show up as noise, heat, or a loose bearing.
Splitting both bearing seats across two halves and expecting them to stay on one axis. Each seat then depends on both halves matching. Alignment is easier when both seats are formed in the same part, on the same side of the tool.
Pressing the bearing into plain plastic on a motor that runs hot. Plastic grows more than the steel bearing, and the press fit relaxes. A metal sleeve lets the steel hold the bearing size.
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 library
Every part-type guide, grouped by family.
Molded parts libraryDrone 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.
Why is a clamshell harder to keep the bearings in line?
Each bearing seat is shared between the two halves, so both halves have to match. A cup with an end bell keeps the stator bore and one seat in one part. The second seat locates on a spigot.
When does the housing need a metal sleeve at the bearing?
When a plastic press fit would loosen after the motor runs hot. The plastic holds the sleeve. The steel holds the bearing size. Send the bearing part numbers and the running temperature with the CAD.
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.