Super Precision Roller Bearings
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Super Precision Roller Bearings
What is a super precision roller bearing?
A super precision roller bearing is a roller bearing made to much tighter tolerances than a standard bearing. Its dimensions, running accuracy, and internal geometry are controlled to within a few microns, so the shaft runs truly with very little runout, vibration, or heat. They are mainly used in machine tool spindles and other machines where the accuracy of the bearing directly affects the accuracy of the finished work.
The most common super precision roller bearings are cylindrical roller bearings. A standard bearing has four main parts:
- An inner ring, which fits onto the spindle or shaft, often on a tapered seat
- An outer ring, which sits in the housing
- One or two rows of cylindrical rollers running between the raceways
- A cage that keeps the rollers evenly spaced.
Many super precision roller bearings have a tapered bore.
- The bearing is pushed up a tapered spindle seat, which expands the inner ring slightly.
- This lets the radial clearance be reduced to almost zero or set to a light preload, which gives the spindle maximum stiffness and accuracy.
Most super precision cylindrical roller bearings are separable, so the inner ring and the outer ring with rollers and cage can be fitted separately. Rings and rollers are usually made from high-grade hardened bearing steel, and hybrid versions with ceramic rollers are also available. Cages are commonly glass fibre reinforced polyamide, PEEK, or machined brass.
Why are super precision roller bearings essential?
They give machine tool spindles the stiffness, accuracy, and load capacity needed to cut metal cleanly and hold tight tolerances. Line contact between the rollers and raceways makes them much stiffer radially than ball bearings, so the spindle deflects less under cutting forces. This means better surface finish, less chatter, and more accurate parts. They can also run at high speeds with low heat, particularly in single-row and hybrid designs.
They are usually used together with super precision angular contact ball bearings or thrust bearings, which take the axial loads. Their boundary dimensions are standardised internationally. So a bearing of a given reference has the same bore, outer diameter, and width, regardless of which reputable manufacturer makes it.
Typical applications include:
- Lathe, milling, and machining centre spindles
- Grinding machine spindles
- Rotary tables and indexing tables
- Printing machines
- Rolling mill roll necks
- Precision gearboxes
- Test and measuring equipment
- Medical and scientific equipment
The main types of super precision roller bearings
- Double-row cylindrical roller bearings (NN 30 series) - These have two rows of rollers, with ribs on the inner ring. They offer very high radial stiffness and load capacity in a compact section, and are the most common choice for machine tool spindles.
- Double-row cylindrical roller bearings (NNU 49 series) - These have two rows of rollers, with ribs on the outer ring instead of the inner ring. They have a thinner section and are often used where the inner raceway is ground after mounting for maximum accuracy.
- Single-row cylindrical roller bearings (N 10 series) - These have one row of rollers and are designed for high speeds. They are used in high-speed spindles where lower friction and heat matter more than maximum stiffness.
- Super precision tapered roller bearings - These carry combined radial and axial loads with high stiffness, and are used in some lathe and heavy machining spindles, as well as precision gearboxes.
- Axial-radial bearings for rotary tables - These combine axial and radial rollers in one ready-to-fit unit. They are bolted directly into rotary tables and indexing heads, giving high stiffness and accuracy in both directions.
- Crossed roller bearings - These have a single row of rollers arranged at 90° to each other, alternately. They carry radial, axial, and tilting moment loads in a very compact space, and are used in rotary tables, robotics, and measuring equipment.
Material variants include:
- Hybrid bearings with silicon nitride ceramic rollers - Lighter and harder than steel rollers, so they run faster, cooler, and with longer grease life.
- PEEK cages - Light and strong, suited to high speeds and temperatures up to around 150°C.
- Polyamide cages - Light and quiet, the standard choice in many sizes.
- Machined brass cages - Very robust, often used in larger sizes and oil-lubricated spindles.
How to choose the right super precision roller bearing?
- Size and dimensions - The bore must suit the spindle; the outer diameter and width must fit the housing. Spindle and housing seats must be machined to matching precision, or the accuracy of the bearing is lost.
- Precision class - Choose the tolerance class to suit the accuracy the machine needs. Higher classes give better running accuracy but cost more.
- Stiffness and load - Double-row designs give the highest radial stiffness and load capacity. Single-row designs give lower friction and higher speeds.
- Clearance or preload - Tapered bore bearings let the clearance or preload be set during mounting. Cylindrical bore bearings are supplied with a set clearance, which must suit the fits and operating temperature.
- Speed and lubrication - Grease suits most spindles and is simple to maintain. Oil-air or oil-mist lubrication allows higher speeds and removes more heat.
- Cage and material - Polyamide and PEEK cages suit high speeds. Brass cages are more robust. Hybrid bearings with ceramic rollers give higher speeds and longer life.
Essential references and specialised ranges
How the numbering works:
The letters at the start identify the design:
N = single-row, with ribs on the inner ring
NN = double-row, with ribs on the inner ring
NNU = double-row, with ribs on the outer ring
The next two digits indicate the dimension series: 10 is the single-row high-speed series, 30 is the standard double-row series, and 49 is a thin-section double-row series.
The last two digits indicate the bore. Multiply by five (for example, NN 3010 = 50mm and N 1016 = 80mm)
Suffixes:
K = tapered bore (taper 1:12)
SP = special precision: dimensional accuracy approximately ISO class 5, running accuracy approximately ISO class 4
UP = ultra precision: dimensional accuracy approximately ISO class 4, running accuracy better than ISO class 4
P4, P2 = ISO tolerance class 4 or 2
TN = glass fibre reinforced polyamide cage
PHA = carbon fibre reinforced PEEK cage, outer ring centred, high-speed design
M = machined brass cage
MB = machined brass cage, guided on the inner ring
HC5 = hybrid bearing with silicon nitride ceramic rollers
W33 = lubrication groove and three lubrication holes in the outer ring
AS = lubrication groove and holes in the outer ring
C1, C2 = radial internal clearance smaller than normal
Suffix codes vary between manufacturers, so check the supplier’s catalogue for the exact meaning.
FAQ - All you need to know about super precision roller bearings
What does “super precision” mean?
It means the bearing is made to tolerances well beyond those of a standard bearing, usually ISO class 5, 4, or 2. The dimensions, running accuracy, and roller sizes are all controlled to within a few microns, so the bearing runs truly and keeps its accuracy at speed.
What is the difference between SP and UP?
SP (special precision) bearings have dimensional accuracy of roughly ISO class 5 and running accuracy of roughly ISO class 4. UP (ultra precision) bearings are tighter, with dimensional accuracy of roughly ISO class 4 and running accuracy better than ISO class 4. UP is used where the very highest spindle accuracy is needed.
Why do many super precision roller bearings have a tapered bore?
A tapered bore lets the bearing be pushed up the spindle seat by a set amount, which reduces the radial clearance or adds a light preload. This allows the clearance to be set very accurately during mounting, giving maximum stiffness and running accuracy.
Do super precision roller bearings need lubrication?
Yes, but the amount is critical. Grease-lubricated spindle bearings need only a small, measured quantity of grease, and too much causes overheating. New grease-lubricated bearings usually need a running-in procedure, where the speed is increased in stages to spread the grease. Oil-air lubrication is used for the highest speeds.
Click here to learn how to maintain a bearing.
Can I replace a super precision roller bearing myself?
It is possible, but it needs a very clean workspace, the correct tools, and accurate measuring equipment. Tapered bore bearings must be driven up the spindle seat by exactly the right amount, which is checked with a gauge. Small errors in fitting, cleanliness, or alignment will reduce spindle accuracy and bearing life, so many machine owners use a specialist spindle repair service.
How do I identify a bearing I need to replace?
The reference is usually marked on the side face of the rings, including the precision class. If the markings are worn away, measure the bore, outer diameter, and width with a micrometer and match them against a size chart. Also note whether the bore is cylindrical or tapered, the number of roller rows, and which ring has the ribs.
Click here to learn how to measure a bearing.
How can I tell if a bearing is worn or failing?
Warning signs include:
- Poorer surface finish or accuracy on machined parts
- Chatter marks during cutting
- Increased noise or vibration from the spindle
- The spindle running hotter than normal
- Play or runout at the spindle nose
- Rough rotation when the spindle is turned by hand
