One for the engineers

[Chrisc]

Boat sanding time is coming up and I have a Bosch Random Orbital sander in which the bottom sealed bearing was whining quite a bit. I have pulled it out, removed the seals, cleaned it out of all the accumulated sanding gunk and all is good - no rattles chips or play in the ball race. Prior to replacing the seals and re-installing the bearing I assume I have to lubricate with something - light oil, heavy oil, some sort of grease? ?? Logic dictates that next time I make the 100km trip to town I buy a new bearing but, waste not..

Chris

[neilpride]

Mate buy a new bearing, cost about 5 $ , if not , some light grease inside in the balls can do the trick , just a litle or the grease start to squeeze out from the seals, i replace 2 bearings in my makita and what a diference, smooth as the first day!!!

[Chrisc]

O.K., thanks. I have a little water pump grease which is quite light. I will try a small dollop of that and see how it goes. But, I'm envious of you buying replacement bearings for 5 bucks. I bought two new bearings for my Makita planer, and they cost me $40 (NZ). I'm still hurting!

[Andrew Troup]

The thing you may not realise is that bearings cost sometimes an order of magnitude less if you buy them from a bearing supplier rather than the equipment supplier (in this case a Makita agent)

Apologies if you already knew this, but if you didn't, just check the yellow pages under "Bearings - Ball Roller etc" or some such.

Nobody makes their own bearings; almost all OEM equipment uses standard bearings available from virtually any of the big manufacturers, like SKF, NTN, Koyo, NSK, FAG, etc etc.

This applies just as much to marine equipment, if not more so. However only a limited number of bearing manufacturers make stainless bearings, although they're a lot more available than a few decades ago.

It used to be that the likes of Torrington and Timken and New Departure made only certain types of bearings, but that trend is almost dead. An exception would be linear bearings...

[Wotname]

Originally Posted by Andrew Troup

The thing you may not realise is that bearings cost sometimes an order of magnitude less if you buy them from a bearing supplier rather than the equipment supplier (in this case a Makita agent)

Apologies if you already knew this, but if you didn't, just check the yellow pages under "Bearings - Ball Roller etc" or some such.

Nobody makes their own bearings; almost all OEM equipment uses standard bearings available from virtually any of the big manufacturers, like SKF, NTN, Koyo, NSK, FAG, etc etc.

This applies just as much to marine equipment, if not more so. However only a limited number of bearing manufacturers make stainless bearings, although they're a lot more available than a few decades ago.

It used to be that the likes of Torrington and Timken and New Departure made only certain types of bearings, but that trend is almost dead. An exception would be linear bearings...

EXACTLY!
Almost only ever bought bearings from the local bearing supplier -CBC or whatever. Except for bearings for sheet winches, they can be difficult to source at times

[Andrew Troup]

Indeed, thanks for that. I didn't think of that example of an exception to the rule: some marine equipment has the "rolling element bearings" (fancy generic covering ball, needle, cylindrical roller, taper roller, spherical barrel roller, etc...) integrated with the design.

By that I mean that one or both raceways is part of the equipment, rather than being a separate ring you get when you buy the equipment. This goes right back to pushbike steering stems and pedal cranks, over a hundred years ago, and loose bearing balls are still sold as 'cycle balls'.

Ball and roller bearing blocks are the most obvious example in the marine sphere where there is no separate 'bearing' as such, but as Wotname points out, winches also generally use needle roller and cage assemblies which are proprietary to the winch manufucturer, ie designed and built in-house, and which use the adjacent surfaces of the compenents as raceways.

Incidentally this is particularly straighforward for needle rollers, where these are simple cylindrical surfaces.

The reasons as I see them are that firstly there is no need for the precision you typically get when you buy an off-the-shelf rolling element bearing, secondly there is a strong need to save space in the radial direction, and thirdly the material selection is crucial when the "lubricant" is seawater. Conventional bearing steels, while high in chromium, are far from "stainless". And stainless off-the-shelf bearings are horribly expensive, available only in limited sizes (mostly the very small ones) and will not carry the same loads.

Roller furling gears sometimes use "off the shelf", non-stainless bearings, to which the slightest exposure to seawater is a virtual death sentence. They seal them so that, in theory, seawater cannot get to them.

I've had mixed experiences with these on other people's boats, but it has always seemed to me such a bad idea that I would never dream of owning such a piece of equipment.

As a general rule of thumb for designing above-decks marine equipment, the situation eventually arises where the crowning achievement of seals is to stop water getting back out once it has got in.

This gets closer to the truth the closer you get to the bow.