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sealed or shielded bearings in woodworking equipment

Bill D

Diamond
Joined
Apr 1, 2004
Location
Modesto, CA USA
I bought a replacement bearing for my wood lathe today. Bearing salesman told me that almost all woodworking equipment that he sees uses shielded bearings instead of sealed. I always replaced with sealed to keep the grease in and the sawdust out. I figured the machines I have replaced bearings in were all older so they did not have good seals back then and used shields instead. Any thoughts on this?
Bill D.
 
If you have no provision for adding grease, then seals are a bit of a no-brainer. Any time you can eliminate foreign matter from entering the raceways, you add life to the bearing.
 
Bill, I'm a pro woodwhacker & I agree with your thoughts. Do the same myself. Unless there is an integral oiling system, bearings in woodworking machines often seem to fail from filling up with sawdust & glue rather than life hours. Portable routers are a good example, but the problem extends even to "industrial" type machines like saws & tenoners if the bearings are not fully enclosed.

smt
 
I seem to remember that when I replaced the bearings on my router, 20,000+rpm, they told me no seals at that rpm. I believe it uses felt seals to hold the grease in.
Bill D.
 
Generally, at high speeds, seals add considerable friction to the bearing causing premature failure. At high RPM's alternatives are employed to keep foreign matter out. At wood lathe speeds, seals will be fine. If you want the certainty of knowing yourself, find the bearing ID number and look up the data online. Or, if you've got an itch to add to your library, the SKF bearing handbook is worth the arm and leg.:D
 
Bill D

Its quite common to find a rotational speed restriction on sealed bearings compared to the shielded version. I've been told that on many good quality bearings shielded versions can be just as good at dynamic sealing as sealed ones. The seals being intended more to stop stuff creeping in when the bearing is at rest. I've also been told that a bearing seal is no substitute for a properly designed external seal.

Clive
 
sealed brgs

In my own ww shop , brgs exposed to planks etc got replace with sealed and sheilded brgs, where those mostly protected get double sealed. Bearings with ZZ in part # are sheilded wth metal , the also come in ZZ sealed to protect from dust etc. One could remove the closure to relub but usually the metal is bent taking it out. A lot of saw mills use the sheild and sealed in pillow blocks for conveyors etc , a crusher I worked on had the sheilded and sealed brg. Good idea in ones home shop in case an errant piece of wood goes the wrong direction.
 
I've also been told that a bearing seal is no substitute for a properly designed external seal.

Clive

that's why they're more correctly referred to as rubber shields and not seals. there are a few special types though that can hold a seal under very light pressure but the majority are just a bit better at keeping out moisture and water than a good metal seal is.



dave
 
Bearing seals contact the inner ring and completely seal the bearing, but the seal is basically a piece of rubber bridging across the bearing's inner ring, so it has a lot more drag than a shield.

[FONT=Verdana, Arial, Helvetica, sans-serif] Bearing shields are just a thin metal foil that doesn't make contact with the inner ring, so they can't protect bearings from small particles or liquid
contaminants, including water, but they have a lot less drag.
[/FONT][FONT=Verdana, Arial, Helvetica, sans-serif]
When you hold a fresh shielded bearing between your index finger and your thumb, you can spin the bearing race. A sealed bearing will just drag along with your finger.
[/FONT][FONT=Verdana, Arial, Helvetica, sans-serif]
Like Dave mentions, there are compromise "Non contact seals"
[/FONT][FONT=Verdana, Arial, Helvetica, sans-serif](the -VV bearing suffix, for example) [/FONT][FONT=Verdana, Arial, Helvetica, sans-serif]and the felt seals used in the KO Lee T&C Grinder workheads (for example), which aren't completely sealed (they don't extend all the way to the inner ring), but have less drag than a sealed bearing.[/FONT]
[FONT=Verdana, Arial, Helvetica, sans-serif]
Most bearing books I've read suggest keeping the same type of bearing: replace sealed bearing with seals, replaced shielded bearing with shields.
[/FONT]
 
In the paper working machinery i deal with its never the rotation thats the problem, the dust just soaks the oil up with sheilded bearings, sealed tend to live a lot longer. Oftern there is no extra provision to seal the bearing so it realy helps to go for sealed over sheilded bearings, This is bellow a few K RPM though. As speed picks up i will agree its a diffrent story, but low rpm i will generaly replace failed sheild style with sealed bearings.

This isnt realy conclusive though as a lot of these bearings are lightly loaded, just chinese rubbish to start with.

It can also get intresting if its the outer not the inner that rotates, more so at speed as it tends to fling the oil - grease out through the interferance fit of the metal shields to the outer race.
 
One instance where you should use SHIELDED bearings is on bandsaws,for the bearings that go behind the blade.When you start to cut,the blade goes back against the bearings,which spin,reducing friction. Sealed bearings will not spin,and will get grooves worn into their races from not spinning.
 
One instance where you should use SHIELDED bearings is on bandsaws,for the bearings that go behind the blade.When you start to cut,the blade goes back against the bearings,which spin,reducing friction. Sealed bearings will not spin,and will get grooves worn into their races from not spinning.

Yeah, I learned this lesson the hard way :)
 
Another vote for seals and a general scoff for the "expertise" of salesmen of any kind, particularly on abstruse technical details such as shields Vs seals. The shielded bearing has a small clearance space between shield and inner race. Over some time, fine dust accumulates to rob the bearing grease of its oil leaving the soap and the starving bearings internals of lubrication.

The pronlen is still present in a seal especally over timewhen the seal lip loses its tension but a sealed bearing is still the preferred for woodworking machinery and power tools. .
 
I'm rebuilding a 42,500 rpm spindle and non-contacting shields seem to be the rule at that speed. For normal speed stuff I can't imagine why one would want anything other than seals to keep the bad out and the good in.
 
I'm rebuilding a 42,500 rpm spindle and non-contacting shields seem to be the rule at that speed.

Almost all spindle bearings I've seen are open, because the races need to be offset to preload them. If you had a shield or seal on the bearing, you'd bend it when you preloaded it.

For normal speed stuff I can't imagine why one would want anything other than seals to keep the bad out and the good in.

There's a horsepower loss with seals, due to the friction and consequent heating issues. The bearing books quote the formula to calculate the loss.
 
I bought a replacement bearing for my wood lathe today. Bearing salesman told me that almost all woodworking equipment that he sees uses shielded bearings instead of sealed.

the above is true but the reason for the shields is purely a matter of economics. Shielded are cheaper than sealed.

In a wood lathe, sealed will outlast shielded.

I always replaced with sealed to keep the grease in and the sawdust out. I figured the machines I have replaced bearings in were all older so they did not have good seals back then and used shields instead. Any thoughts on this?
Bill D.


Use sealed as you have been. Your bearings will last longer.
Some of the old bearings are sealed but look like shielded bearings. Take a look at the Felt Sealed line of beaings for an example.
 
Last edited:
Pierce-

Last order was from Accurate, so realized I better go check the drawer. I have gotten NOS ND from someplace, but apparently this was not it. The ND's seemd to be longer lasting, nicer bearings in severall applications, at least "personally anecdotal" in my shop. I have some legacy Milwaukee routers that had shop made fixturing for them such as tilt base, modified bases, base in an automatic machine, etc. that makes it easier to change bearings as needed, than to go to a different router system and make new tooling. (I have several other and newer routers for routine tasks & heavy work, but the Milwaukees have a place & I still like their compact size and relatively "solid" configuration.

Good catch.

In fact the "new" bearings are not even rubber sealed, (which is an option), but mechanical labyrinth on exposed side, shielded inner side. Fafnir calls it "one side shielded, one side sealed" but in checking the catalog notes for this post, the "sealed" side is mechanical for LD series, P series are rubber. Fafnir 202KLD3 So will just have to see how they last.

Apologies for the confusion. Still, in keeping with the OP, where applicable i do prefer sealed bearings for woodwhacking equipment.

smt
 
If the bearing is for the spindle and the spindle housing is totally enclosed
to keep dust out then you might be ok. But in woodworking dust collects every
where as you know. Sealed is the way to go. The shielded bearing at first
sounds like a good idea, you can add lube. But you can also add too much lube
and then the balls within the bearing will slide and not roll, causing premature
wear. Inside a motor which has zerk fittings to add lube to the motor shaft ends
a shielded bearing can be used. But what I like to do is remove the rubber seal
from one side of a sealed bearing and that side goes into the bearing cup of the
motor end plates. The sealed side is on the side next to the windings on the
rotor.
 








 
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