GRA 30 ring gauges
SKF ring gauges in the GRA 30 series (fig.1) are typically used to check tapered shaft seats for cylindrical roller bearings in the NN 30 K series. Shaft seats for bearings in the NNU 49 BK and the N 10 K series can also be checked with a GRA 30 series gauge.
GRA 30 ring gauges are available for tapered seats with d ≤ 200 mm. For seats with d > 200 mm, SKF recommends using a taper gauge. Ring gauges for d > 200 mm would be difficult to handle because of their weight.
GRA 30 ring gauges are used primarily to determine the position of the tapered seat relative to a reference surface on the shaft. The reference face of a GRA 30 ring gauge is on the side of its large bore diameter. The reference surface on the shaft may be either in front of, or behind the gauging face of the ring gauge. GRA 30 ring gauges can also be used to check whether the centreline of the tapered seat is at right angles to a reference surface on the shaft. This is achieved by measuring the distance between the reference face on the ring gauge and the reference surface on the shaft at several positions around the circumference.
Taper form errors can be detected using blue dye.
Tapered seat dimensions
SKF recommends using the tapered seat dimensions for bearings in the NN 30 K series listed in the product table. If other dimensions or bearing series are used, the reference length Bc should always be longer than Bb, the width of the intermediate spacer ring (→ product table). This is necessary because the bearing will be driven up further on the seat than the ring gauge, depending on the bearing internal clearance or preload that should be achieved. Therefore, always make the reference length longer than the width of the intermediate ring at least by a value corresponding to the difference Bc – Bb (→ product table).