I have just removed the top wheel from my bandsaw to replace the tyres and thought I should probably replace the bearings whilst I was at it. One is particularly rough. I don't have a bearing puller so I haven't been able to remove them. They are stamped and possibly IMI. I can only find as a self-aligning bearing, is that right? I would have thought you could get a standard bearing too in the same size?

You will get efficient and thoughtful service from Rimao.

You probably can, but on my bandsaw the wheels can be adjusted angularly so the blade tracks correctly. I presume they need to be self-aligning so as to obtain this adjustment. If they're rigid you may be unable to get the blade to run well and it might keep coming off.

A self aligning bearing would (theoretically) allow the wheel to twist slightly to equalise the load across the blade. Presumably this would reduce stress and wear on the tyre.

I'm somewhat dubious of the physics of the idea as the wheel will effectively be stabilised only by blade tension variations rather than rigidly by the bearing. Sounds to me like crowned pulleys evil cousin!

Clive

Tried to fathom what all has been said here and failed…How would a self aligning bearing do duty in this application? My understanding of such a bearing is that the inner race and outer cage can be on non-aligned axes and are not constrained. If this bearing were used in the bandsaw wheel the wheel would just flop about its axis all the time! Also, such bearing cannot be sealed and so sawdust would enter and destroy it soon anyway..

All the bandsaws I ever used had two normal bearings in the upper wheel, onto a shaft that tilted and so tilted the wheel. Where does the self aligning bearing fit??

The wheel has bearings which fit onto the shaft that tilts – the bearing cannot 'tilt'!

Makes no sense to me…

Joe

I spent some time digging out the congealed grease and although I cant be sure I think it is a standard bearing even though the part number stamped on it would suggest a self aligning. I can only see 8 balls and their diameter would suggest only ring of ball bearings.

In light of further comments, I may revise my previous posting I'm wrong again.

I was envisaging a pillow block type of arrangement where one end of the shaft could be moved up and down by a screw mechanism to induce tilt, the movement being between outer race and housing, rather than outer and inner race.

But there would need to be a bearing of some sort where the screw mechanism is, so not as simple as I first thought.

However, you CAN apparently get sealed self-aligning bearings, so something learned anyway

Rob

Bandsaw wheels are crowned to allow the blade to track. Each wheel must be aligned so the crowns run in the same plane. Each wheel must be constrained by it's bearing and usually one of the bearing housings is adjustable for into and out of the common plane and for tilt. If you fit self aligning bearing the wheels will just flop about and the blade will come off. Effectively the bearing must oppose the crowning forces not just allow the wheels to fold inwards.

Probably not as clear an exlanation as some might give but that's it for now.

If you are looking for more details, kindly visit Self-Aligning Ball Bearings.

regards Martin

Hi, a is a self aligning double row ball bearing with either a parallel inner race that fits on the journal or a tapered inner race that is normally locked onto the journal with a tapered sleeve. Self aligning bearings are normally used as Dave Halford has said, where the bearing mountings are not guaranteed to be totally inline with each other, i.e. not on a truly flat plain.

Regards Nick.

Posted by Martin Kyte on 28/02/ 22:13:10:

Bandsaw wheels are crowned to allow the blade to track. Each wheel must be aligned so the crowns run in the same plane. Each wheel must be constrained by it's bearing and usually one of the bearing housings is adjustable for into and out of the common plane and for tilt. If you fit self aligning bearing the wheels will just flop about and the blade will come off. Effectively the bearing must oppose the crowning forces not just allow the wheels to fold inwards.

Probably not as clear an exlanation as some might give but that's it for now.

regards Martin

Bandsaw wheels aren't always crowned. In Italy they are mostly flat. Flat wheels are better with wider blades, to run a narrow blade you need a crown.

There are 2 sorts of self aligning bearing ! Those that have the OD of the outer race curved and a coresponding housing that it moves in to allow alignment of the shaft. I have seen round, square, oval and a plummber block type housings. The other type the ID of the outer race is curved to allow the balls and inner race to align with the shaft..

Noelt

Self-Aligning Bearing Guide And Overview

Figure 1: Self-aligning bearing

Self-aligning ball bearings are ideal for applications with misalignment issues between the shaft and housing. Due to their design, self-aligning ball bearings can accommodate up to 3° of misalignment without increasing the amount of friction and frictional heat produced. However, as the contact angle is relatively small on these bearings, the axial load capacity is not as high as, for example, angular contact bearings. These bearings can handle both static and dynamic misalignments. A sealed self-aligning ball bearing also protects it from dirt and other contaminants. Self-aligning ball bearing applications can be found in various industries, such as mining, food processing, and mass production use, such as the textile industry.

Table of contents

• Self-aligning ball bearings construction
• Advantages and disadvantages
• Mounting a self-aligning bearing
• Selection criteria

Self-aligning ball bearings construction

Self-aligning ball bearings consist of an outer ring, an inner ring, rolling elements, a cage to house the rolling elements, and seals that protect the balls from contaminants and other dirt. Due to their design, these elements make it possible for self-aligning bearings to counteract any static or dynamic misalignment of a shaft and housing assembly up to 3°. They also generate far less heat than other bearings due to the low friction within the bearing, allowing them to run cooler than other bearings at higher speeds. Self-aligning bearings work by utilizing a design with two rows of balls or rollers separated by a spherical raceway.

• Outer ring: The outer ring of the bearings has a smooth spherical shape without raceways. The shape of the outer ring allows for slight movement within the bearing, which in turn allows the bearing to self-align.
• Inner ring: The inner ring of the self-aligning bearing has two raceways that keep the balls and cage in place.
• Rolling elements and cage: The rolling elements on self-aligning ball bearings are kept in place by the cage and the inner ring. As there is a loose configuration between the balls and the inner and outer ring, friction and frictional heat are very low. The cage is typically stamped steel, PA66, reinforced glass fiber, or machined brass.
• Seal: A sealed self-aligning ball bearing ensures dirt and other contaminants don't affect the bearing rolling elements.

Advantages and disadvantages

There are many advantages of self-aligning ball bearings over other bearing types, such as tapered bearings, deep groove ball bearings, and other ball bearing types. However, self-aligning ball bearings do not perform as strongly in terms of load-carrying capacity.

Advantages

• Misalignment: Self-aligning ball bearings can counteract static and dynamic misalignment of up to 3°.
• Service life: These bearings offer excellent high-speed performance and generate far less heat and friction than other ball bearing types. This allows them to run cooler and extends their service life while reducing maintenance.
• Light load performance: This type of bearing has very low load requirements, which means they perform excellent, even under light loads.
• Low noise: Self-aligning ball bearings produce low noise levels due to the loose conformity between balls and the outer ring. This makes them especially suited for use in household items such as fans and air conditioning units.

Disadvantages

• Load types: The ball bearings on self-aligning ball bearings are mounted at a relatively straight angle between the inner and outer ring. This means that the load types the bearing can handle is radial, with little axial load carrying capacity.
• Load amount: As ball bearings have a small point of load-bearing contact, the amount of load this type of bearing can handle is relatively small.

Mounting a self-aligning bearing

Most self-aligning ball bearings will be mounted using an adapter sleeve. In the below steps, we explain this procedure:

1. Bearings often come with a protective film that protects the components from outside influences during transport. Make sure to remove this film before mounting the bearing
2. Oil the exterior surface of the bearing with oil or grease.
3. Apply oil to the adapter.
4. Open the adapter slightly with the help of a screwdriver and slide it in place on the shaft.
5. Once the adapter is in the correct position, position the bearing on the adapter sleeve. If the shaft has threads, it will help to use a nut to bring the bearing in the correct place; if not, use a bearing pusher kit or a small mallet.
6. Once the bearing is in place, test the rotation of the bearing on the outer ring. It should be able to rotate freely, but not swivel.
7. Lock the bearing in place with a locking washer by first removing the nut, placing the washer in place, and putting the nut back again.

Note: If the adapter sleeve is loose or not properly secured in place, the inner ring can start turning on the adapter sleeve. This causes excessive friction between the three components and can damage the shaft, adapter, and bearing.

Figure 2: Mounting a self-aligned bearing ball-bearing-self-align.jpg

Selection criteria

When selecting self-aligning bearings, the primary considerations revolve around any possible alignment problems, rotational speed, load type, load size, tolerances, and bearing dimensions:

For more information, please visit Thrust Ball Bearings.