Easy assembly of plain bearings – with these 3 tips
Lars Butenschön | 30. March 2020
There are many ways to install a plain bearing: gluing, press-fit, screwing or clipping on by means of various snap-in functions.
By default, most plain bearings are designed to be press-fitted. In theory this sounds very simple. In practice, however, many a stumbling block lurks. Especially plain bearings with thin wall thicknesses or those made of rather brittle materials may break if you “press-fit” them too robustly with a hammer. To exclude these problems from the outset, we show you here 3 tips with which you are guaranteed to install plain bearings quickly and without broken pieces.
Tip 1: Observe the installation tolerances
Most plain bearing manufacturers indicate installation tolerances in their respective specifications and product data sheets. This means not only the tolerances of the plain bearings, but also the tolerances of the housing hole and shaft. An example: a simple cylindrical bearing bushing from igus with an inner diameter of 10mm and an outer diameter of 12mm is designed for installation in a housing hole with 12 H7. The plain bearing itself is manufactured oversized, i.e. with larger tolerances. In practical terms, the assembly will require a little effort. Once the bearing is installed, the press-fit holds it securely in the hole. This is necessary so that the bearing does not rotate with the shaft in the housing hole or even move out. The outer diameter tolerance of the plain bearings depends on many factors. In the definition, manufacturers must take into account, for example, the thermal and moisture expansion of the bearing material. Manufacturing tolerances also play an important role.
Tip 2: Use a press-fit aid
Ideally, you should install plain bearings directly with a hand press. These devices have a simple design and allow a repeatable press-in process (but be careful with your fingers!). Use a flat press-in punch. Centring mandrels are supposed to help during insertion, but they break off, especially in the case of plastic bushes with flange. Simply insert the bushing into the holder with chamfer first. The press does the rest. The chamfer also helps to bring the bushing in straight, even if it is slightly “tilted”.
Of course, especially on construction sites or during the maize harvest when the machine has just collapsed and there is an urgent need to replace bearings, there is a shortage of hand presses. It is also not always practical to insert 30kg hydraulic cylinders into the press to press the bearing into the cylinder eye. The handyman therefore reaches for the mobile hand press model, steel-on-wood handle, and installs the bearing at the designated location according to the motto “What doesn’t fit, is made to fit”.
So here’s a top handyman’s tip: it’s better to opt for the rubberised version. If the rubber mallet is also not at hand, at least hold a wooden board or similar between the bearing and the hammer.
Tip 3: Chamfer housing hole
… or at least deburr. Sharp-edged housing holes are very suitable for stripping plain bearings. This does not necessarily have to lead to the destruction of the bushing, but in the case of plastic bushings in particular, it often results in greater bearing clearance due to a corresponding deformation. A further consequence, which is often noticed too late, can also be greatly reduced bearing clearance if, for example, the swarf removed during press-fit comes between the bearing and the hole. The result: the bearing narrows accordingly. In other words, deburr the housing holes at least cleanly, or better still, apply a simple chamfer. This removes the burr immediately and ensures easy centring and pressing in of the bearing.
Do you have any questions? We advise you!
These were just some of the many experiences we have had in practice. Nevertheless, together with our customers we master new interesting challenges every day, which by far exceed the scope of this blog post. Contact us, and we will support you in the design and selection of your plain bearing solution.