Measuring of standard catalogue bearings

Fred Lu | August 7, 2020

iglidur® bearings are press-fit bearings for bores with a H7 standard bore. On the one hand, this press-fitting fixates the bearings in the housing and on the other, the inner diameter of the bearings is formed by that and finally creates the proper inner tolerance.

If you measure the loose bearings as delivered, the inner- and as well the outer-diameter are always bigger (up to ~0,5 mm)

The inspection of the bearing, installed in a bore with minimum size, takes place both with a dial gage and a pin gage. (compare Fig. 1)

Press-fitted in the bore, the go-side of the gage must smoothly pass the bearing.

At the measuring levels (compare Fig. 2), the inner diameter of the bearings must lie along with the Dia tester within the specified tolerance.

Why we use a pin gauge

At a larger scale, the inner surface of a bearing is uneven. (compare Fig. 3) A caliper only measures a fraction of the inner diameter and could also push into the soft material.

A pin gauge reflects the realistic conditions the best way. It ignores small edges and is the best comparison to the shaft in the application. (compare Fig.4) To make sure, that the bearing has no curved inner structure, we double check with the Dia tester.

Causes of the measurement variations:

Despite careful manufacturing and installation of the bearing, variations and troubles connected with installation dimensions and tolerances can arise. Due to this reason, we have listed the most frequent causes for variations. In many cases the causes for variations can be quickly found with this troubleshooter:

• The bearing is not press-fitted
• The inner diameter is measured with a caliper gauge
• Bore is not properly chamfered – the bearing scrapes off on the outside.
• A centering pin is used to enlarge the bearings’ inside when it is pressed in.
• The bore does not correspond to the H7 tolerance.
• The housing is made of a soft material that gets enlarged by the bearing when pressed in.
• The shaft is not H-tolerant.
• The measuring doesn’t take place within the measuring lines.