SKF71936ACDP4ADGASuper Precision Angular Contact Ball Bearing Matched Set 180 x 250 x 33 mm, 25° Contact Angle, P4A / ABEC 7 Class, Extra-Thin 719 Section, Universally Matched Extra Light Preload, 2 Pieces

Product Description

What this part is

A universally matched set of two super precision angular contact ball bearings in the 71936 envelope — 180 mm bore, 250 mm outside diameter, 33 mm width per bearing. This is SKF’s spindle bearing range: single row, open, and ground so the pair can be clamped up in any duplex arrangement and will come to the intended extra light preload without shims.

Decoding the designation

71936 — ISO boundary dimensions in the extra-thin 719 dimension series: 180 x 250 x 33 mm. The 36 is the bore code, 36 x 5 = 180 mm.
AC — 25° contact angle in SKF nomenclature. Worth naming the scheme: SKF uses AC for 25° where FAG uses E and NSK uses A5 for the same angle, and where a bare A in NSK means 30°.
D — SKF super precision spindle bearing design.
P4A — SKF super precision tolerance class, ABEC 7 running accuracy with tighter dimensional control.
DGA — a matched set of two (D), universally matchable, extra light preload (GA).

What these specs mean in practice

The 719 series is the thinnest section SKF makes in a spindle bearing. At 180 mm bore the ring wall is only 35 mm of radial section, and that slimness is the design intent: less mass to accelerate, a smaller outside diameter so the spindle housing stays compact, and a smaller ball pitch diameter than a 70xx or 72xx section would give at the same bore. All of that raises the speed the bearing can run. The cost is load capacity and sensitivity to the seat — a thin ring in a large diameter takes up whatever shape the housing gives it, so the housing has to be right.

A 25° contact angle is the middle setting in the spindle range. Against a 15° bearing it carries considerably more thrust and gives a stiffer axial response; against a 30° or 40° bearing it runs faster and generates less heat. Extra light preload keeps internal friction and heat generation low and permits high speed, at the cost of some stiffness.

Quantity and configuration

This listing is a set of 2 pieces — a universally matched pair. Because the ring faces are ground to match, you can stack them back to back (DB) for maximum moment stiffness and thrust in both directions, face to face (DF) where the housing bores may be slightly misaligned, or in tandem (DT) to double thrust capacity in one direction. Clamping the pair between the shaft shoulder and the locknut develops the built-in extra light preload; do not add shims or a spacer unless you intend to change the preload deliberately.

Fitting notes

Super precision bearings only deliver their accuracy on seats ground to match, and a 719-section bearing is more sensitive to this than most. Hold shaft journal and housing bore runout and roundness to a few microns, keep the abutment faces square, and make sure the housing bore is continuous and evenly supported rather than a bolted assembly with soft spots. At 180 mm bore, thermal mounting is the practical method: heat the inner ring evenly in an induction heater or oil bath to a controlled temperature and slide it onto the journal. Never press through the balls and never use a torch. Keep the pair oriented as marked — reversing one bearing changes the preload. Lubricate with a spindle grease or an oil mist or oil-air system sized for the bore and speed, and keep the fill light.

Interchange guidance

Same-envelope 25° super precision equivalents include FAG B71936-E-T-P4S-UL, NSK 71936A5, NTN 71936 and RHP 71936-E-T-DUL-P4 in the corresponding precision grade. Within SKF, 71936 CD/P4ADGA is the 15° version of the same envelope — identical dimensions, different contact angle, and not a substitute inside an existing preloaded set. 71936 ACD/P4ADGB and DGC are the light and medium preload versions. When cross-referencing, match the contact angle and the preload, not just the base number.