CNC Turned Aluminum Bearing Cover Discs
Bearing cover discs turned from 6061-T6 bar, with a spigot held to H8 and 0.015 mm roundness, a sealing face lapped flat to 0.01 mm, a bolt circle positioned to ±0.05 mm and a recess depth held to ±0.05 mm. Discs are supplied in pairs matched to 0.03 mm in thickness so a shaft is covered evenly at both ends.
- Spigot Fit to H8
- Sealing Face Lapped 0.01 mm
- Bolt Circle ±0.05 mm
- Discs Matched in Pairs
*Send the housing bore and the bearing outer diameter. The spigot is cut to the housing, and a disc turned to nominal will either be loose or need to be pressed in.
Bearing Cover Disc Overview
A cover disc closes a bearing housing and holds the outer race in place. Its spigot centres it, its face seals it and its bolt circle clamps it. If the spigot and the face are not machined together, the disc cocks and the seal weeps at one side.
The disc is turned from bar in one operation: face, spigot, recess and outside diameter, then the bolt circle is drilled from the same centre. The sealing face is lapped after turning and the part is checked on granite before anodizing.
6061-T6 Aluminium Bar
6061-T6 is used for covers on aluminium housings because the two expand at the same rate, so the spigot fit does not change when the gearbox warms up. It also anodizes to a predictable thickness on the spigot when masked.
6082-T6 or Steel
6082 is the European equivalent and is used where the certificate must match a standard. Steel covers are specified where the disc also retains a bearing preload spring and the bolt threads must not pull out of aluminium.
Match the cover to the housing material wherever the operating temperature swings; a steel cover in an aluminium housing loosens its spigot when hot.
Bearing Cover Disc Specifications
Turning data for cover discs, with the spigot, face and bolt values that decide whether the bearing stays covered and dry.
| Specification | Machining Data | Specification | Machining Data |
|---|---|---|---|
| Product | Bearing Cover Disc / End Cap Disc | Machining Process | CNC Turning, Facing, Drilling |
| Material | 6061-T6 Aluminium Bar | Diameter Range | Ø 50 – 320 mm |
| Spigot Diameter | Ø 30 – 280 mm, H8, Roundness 0.015 mm | Sealing Face | Flatness 0.01 mm, Ra 0.8 µm |
| Disc Thickness | 6 – 30 mm | Bolt Circle | 4 – 12 Holes, Position ±0.05 mm |
| Concentricity | Spigot to Bolt Circle 0.03 mm | Recess Depth | ±0.05 mm |
| Surface Finish | Ra 1.6 µm Faces, Ra 0.8 µm Spigot | Pair Match | Thickness Within 0.03 mm |
| Customization | Grease Nipple, Sight Glass, Sensor Boss | Lead Time | 5 – 7 Days Sample, 10 – 14 Days Batch |
| Inspection | CMM Spigot and Bolt Circle, Granite Flatness, Pair Thickness | Packing | Face Protected, Pair Boxed, Foam Separators |
Key Features of Our Cover Discs
Spigot, face and bolt circle from one centre.
Spigot and Face in One Operation
The spigot and the sealing face are turned without reclamping, so the face runs square to the spigot and the disc does not cock when bolted.
Sealing Face Lapped
Lapping brings the face to 0.01 mm flatness and removes the turning mark that a gasket or O-ring would otherwise follow and leak along.
Bolt Circle From the Spigot Centre
Holes are drilled from the spigot centre to ±0.05 mm, so the disc drops onto the studs without opening the holes or stressing the face.
Pairs Matched in Thickness
Discs for both ends of a shaft are measured together and finished within 0.03 mm, keeping the bearing preload symmetrical.
Cover that has to seal a bearing housing?
Surface Finishes for Cover Discs
The spigot and face are fits; the outside face is visible and only needs corrosion protection.
| Finish | Main Purpose | Finish | Main Purpose |
|---|---|---|---|
| Type II Anodizing | Corrosion protection and colour on the visible disc | Hard Anodizing | Wear resistance where a seal lip runs |
| Masked Spigot | Keeps the spigot fit at H8 | Bead Blasting | Even matte before dye |
| Laser Marking | Bearing size and rotation direction | Bare Sealing Face | Keeps the lapped face flat and uncoated |
*Anodizing adds 5 to 10 µm and will close a H8 spigot. Spigots are masked, and the sealing face is always left bare so the lapped flatness is preserved.
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Turning Process for Cover Discs
The spigot and the sealing face are turned in one operation, so the disc seats square in the housing instead of being pulled in by the bolts.
01. Housing and Bearing Review
Check the housing bore, the bearing outer diameter and the bolt pattern, and confirm whether the disc carries a seal or only a cover.
02. Turn Face and Spigot
Face the disc, turn the spigot to H8 and cut the recess in one operation, checking the spigot with a micrometer before parting off.
03. Drill the Bolt Circle
Drill the bolt circle from the spigot centre, counterbore where specified and deburr both faces of every hole.
04. Lap the Sealing Face
Lap the sealing face flat to 0.01 mm, check it on a surface plate with light behind a straight edge, then clean the part.
05. Mask, Anodize, Check
Mask the spigot and the sealing face, anodize, then CMM the bolt circle and re-check the spigot diameter after coating.
Send the housing bore and the bearing drawing, and we will quote discs with the spigot and face machined together.
Bearing Cover Disc FAQs
H8 in the housing bore gives a light push fit that still centres the disc. A tighter fit needs the housing measured, because a disc turned to nominal will not enter a bore at the low limit.
A turned face has a spiral feed mark that runs from the inside to the outside, which is a leak path under a gasket. Lapping crosses the mark and brings flatness to 0.01 mm.
By about 10 µm, which is enough to make an H8 fit tight. Spigots are masked, and the sealing face is left bare so the lapped surface is not disturbed.
Yes, a tapped boss or a drilled and tapped hole is added before lapping, positioned so the nipple clears the rotating parts inside the housing.
Both discs are turned from the same bar and measured together, then finished to within 0.03 mm in thickness. The pair is boxed together with the match number.
320 mm diameter, which covers most bearing housings up to a 280 mm spigot. Larger covers are machined as a ring and a plate, bolted and sealed.
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