Bearings Breaking

[IL Bull]

Help!
I was sawing a 36" maple log so I had my blade tension jacked up pretty high.
Halfway through my third cut my blade broke.  When I installed a new blade,  it slipped off of the drive wheels.  I was adjusting my tracking when I noticed that 1 3/16 saddle bearings closest to the band wheels on both sides were broken.  I replaced the bearings and was sawing along for about a half of an hour and another bearing broke on the Idler side.  What can be happening?  I have had this saw for a year and a half (Burg All Manual Band Saw) and this has never happened before.  Any Ideas?
Thanks,
Joe

[Jeff]

Welcome to the forum IL Bull.  When you say Saddle bearing, is that what I would refer to as a pillow block bearing? We had trouble on a brand new circle mill years ago with bearings getting ate up or broke on a hydraulic shaft. Turned out that the shims ujder it did not go the full length of the bearing, and the bottom of the bearing was recessed, not solid. When you would torque the bearing down, the case would distort because of the improper shim. It took us a long time to catch it, lots of bearings and head scratching and down time.

I would say if you are having the bearing castings break that your bearing mounting surface is somehow flawed or distorted or improperly shimmed.

[IL Bull]

Yes,  I meant pillow block bearings.  The castings were not broke.  Just the insert.  All I replaced was the insert.  The bearings are self centering.  I ran the saw last night for about an hour with no problems.  The bearings are greaseable and I give them a squirt with every tank of gas.   

[Jeff]

You can have self centering bearings, but still have a distorted case that will take out the bearing. Greasing every tank full of gas I think is probably a little much, but go by the bearing maintenance specs you get with every bearing.

Make sure that the base the pillow block is mounted to is absoluted flat and level. Only a few thousands bend in the mount will cause the bearing case to flex when you torque down the bearing and cause premature bearing failure.  When you put the new bearing on, did you give the idler wheel a spin? How did it turn?

[IL Bull]

Yes,  after I installed the new bearings both wheels spun just fine.  I was wondering if I was over greasing the bearings but I don't know why that would cause them to break.

[D._Frederick]

The quality of the bearing may be too poor for the load you are applying. If you bought off-shore made bearings, the 1 3/16 inch bearings may not be rated for the load. For a 1 1/4 X 0.042 band blade, the strain is about 2200lbs for a carbon blade.

Buy bearings from American companys for better quality and grease them only about once a year unless you use the mill every day. If you overgrease the bearing, the bearing cage can be damaged resulting in failure.

[IL Bull]

The bearing inserts I bought were from our local farm store and were off shore bearings.  The bearings did not have a load rating on them.  The bearing on the drive side has not failed since I have installed it.  They were both the same brand,  junkineeze.

[Jeff]

Sounds like that could be your problem.

 At the Mill where I worked, we demanded good bearings and roller chain. If you didn't put on the good stuff, you end up spending way over the original savings. The down time and repair time at a big mill will kill ya. Its not the cost of the bearings or chain near as much as the lost production and the cost of guys standing around pretending to sweep sawdust.

[Jason_WI]

Avoid chinese bearings like the plague. They use larger balls for the same size bearing which means that the outer race is thinner and will break under load. Bearings made in the USA, Germany, or Japan are the only ones to use.

We found this out the expensive way on our round baler. Chinese bearing from NAPA cost 5 bux and lasted mabe 1/2 day befor the outer race cracked and fell apart. American bearing 30 bux and still on the round baler.

Jason

[wiam]

Jason,  What brand of baler.  I have had the same issues with asian bearings.

Will

[Jason_WI]

wiam,

We have an older Krone 4x5 bround baler with mini stop. It is yellow and red in color. The bearing that I am refering to on this baler support the outside of the chain that spins the bale. They are held on the shaft by a snap ring. The cheap bearings wouldn't last a day. The bearing in on the end of the shaft on the bottom picture of this page:

Krone Link

Jason

[IL Bull]

Well I have learned my lesson on buying cheap bearings.   
Does any one have an opinion on why they broke in the first place?

[D._Frederick]

What is the failure mode of the bearing? Are any of the cast parts broken?  If you have over greased the bearing, the ball cage will fail allowing the balls to go to the bottom of the bearing causing the bearing to be loose.

[IL Bull]

The first failure was when both bearings broke after I snapped a blade.
Both of them had a fractured outside race. 
The next failure was after I installed new bearings.  This was on the Idler
side and the inside race was broken.  No blade breakage.
No cast parts were broken and I am still using the original saddles.
Would over greasing beak a race?   I have not changed how often I greased the bearings since I received the mill.  I have a background in heavy equipment repair (I am the service manager for a Case constuction equipment dealership) and have never known that over greasing caused problems.

[flip]

My guess is probably an imbalance issue with the wheel.  It may not be noticeable but if the heavy spot always ocurrs at the same point it could put enough stress or hammer into the bearing.  One question....were the bearings cracked in the same place-meaning before you took them off the shaft were the cracks in a straight line when viewed from the back of the mill??

[IL Bull]

Only the bearings next to blade wheels were broke.   The bearing on the other end of the shafts were ok.

[flip]

Check wheel and shaft runout, sounds like ya got sumpthin' bent.

Flip

[D._Frederick]

It is my understanding that on a ball bearing over greasing causes additional stress on the cage that hold the individual balls in position around the race. Being made of light weight metal or plastic, it will break allowing the balls to collect in one place on the race.

Your failure sounds just like poor quality bearings that some manufactures are now using to reduce thier costs.

[Brucer]

If your bearings are splitting right around the perimeter of the bearing (instead of across the race), then you probably have a fatigue problem. The fact that it's the bearings closest to the blade that fail indicates that radial (sideways) loads are causing the failure. However, there could be a lot of other things besides blade tension that are the real culprits.

Jeff's comments on having the bearing bolted absolutely flat are right on. This problem often goes undiagnosed. However, it becomes less significant as the bearings get smaller and the loads go down. Self aligning bearings don't always align perfectly. They have a friction fit with the housing to prevent them from turning in the pillow block, and this can prevent the bearing from aligning properly. With the blade off, slack off the mounting bolts and see if a feeler gauge will fit under one or more corners of the pillow block. Even a couple of thou could be a problem.

Too much grease will cause a medium- to high-speed bearing to overheat. This can cause lubricant to break down and it can also lower the strength of the races. This reduces the fatigue life. Regreasing at every refuelling sounds really excessive. Adding too much grease when you do add it can also blow out the seals, causing dirt to get into the bearing.

Do you wipe the top of the grease nipple (with a clean cloth) before adding grease? If you don't, you're injecting a bit of dirt every time you regrease.

Do the replacement bearings have the correct seals? Bearings may be open on one or both sides (probably bad in this case), they may have shields instead of seals (bad again), or they may have seals.

The bearing clearance could be a factor if you're buying cheap imports. There are several suffixes in a bearing number that indicate fit and clearance. When you buy a generic replacement, the salesperson may just look at the main number (size) and ignore the suffixes. If your clearances are too small, you could be putting extra stress on the races and this will lead to fatigue.

Quality may be an issue, as others have mentioned. You'll find good bearings made in the US, Sweden, Germany, Japan, Canada, and a number of other countries. You'll also find bad bearings made in these countries, so your safest bet is to look for manufacturers that are know for quality products. Browning, SKF, FAG, NTN are a few that come to mind.

That's a few thoughts off the top of my head. It's a good idea to hang onto all the pieces when a bearing fails. Then you can show it to a specialist (or post pics on the web) if the problem persists.

[Swede]

Only use bearings of US or European quality! They also has to be rated for 1000 rpm. or more. Changing my bearings I went from the old type with two screws in the inner ring to locking on the shaft by conic sleeves, SKF or NTN. This for geting the shaft in center of the bearing.
Don´t turn the nut too hard, then the inner ring will be wider and the bearing will break.  There may not be an axial stress between the bearings!

1 3/16" sounds too weak, on my saw mill there is 40 mm. (1 1/2"=38,1 mm.)

Swede.