Why are bandsaw thrust bearings sideways? - Woodworking Talk - Woodworkers Forum
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post #1 of 17 Old 12-16-2016, 01:05 PM Thread Starter
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Why are bandsaw thrust bearings sideways?

I just got an old Walker Turner bandsaw up and running. It was missing a lower thrust bearing so I built one using a roller skate bearing. But I built it so the blade rides on the outside of the bearing not the side. YouTube video link below.

I have gotten some feedback that I have created something dangerous. I do not understand why. Can someone explain to me why thrust bearings are sideways? It seems to me that it introduces friction, noise, and odd forces sliding along the blade. Pressing on the outside of the bearing should be less friction. So why are they always sideways?


Installed bearing shown at 5:25 mark.

Last edited by ku3kyc; 12-16-2016 at 03:37 PM.
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post #2 of 17 Old 12-16-2016, 01:33 PM
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I was as puzzled as you when I first encountered this. upper and lower thrust bearings are sideways on our grizzly. and the bearing callout is not even rated for thrust forces?? I have had to replace them because they do wear until they fail.


the only thing I have ever surmised is that the same wear on the edge will cause the outer race to cut in half and the bearing pieces could fly everywhere. that's all I have.


while researching carbide resaw blades yesterday, it said that any bs blade rubbing on the thrust bearing is short for this world. we gap our blades a little over 1/16" away from the thrust brg.
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post #3 of 17 Old 12-16-2016, 03:36 PM Thread Starter
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So I keep an eye on the bearing for wear. I have a pack of skate bearings that cost like $1 each. Changing it out would take a minute or two.

I still don't see a reason to turn the bearing 90 degrees.
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post #4 of 17 Old 12-16-2016, 03:42 PM
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they are not all riding on the side - sold as an "upgrade"
http://www.carterproducts.com/band-s...onversion-kits

if one compares the hardness of 52100 bearing steel to bandsaw blade steel, you won't be replacing the bearings all too often.
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post #5 of 17 Old 12-16-2016, 03:46 PM
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Just my understanding, based on engine bearing uses and tires on pavement ... probably not THE reason, but it makes some sense to me.
On a bandsaw, the thrust bearing is to stop the blade from "going any farther" when it's being pushed on too hard. This means there is already a little twisting to the blade before it contacts the bearing. But that twist can happen between the cutting area and the bearing, leaving the blade cutting a truer path.. If the blade were to make contact long enough to spin up the bearing, the chances of the blade sliding completely off the bearing and continuing back are very high. That could then result in a blade failure.

The bearing is not designed to be in constant contact. Constant contact could transfer the twist back up to the cutting area and cause the blade to walk off course.

By placing the bearing at 90 degrees to the blade, it never is fully spinning at the same speed as the blade, and retains a little better "grip" to keep it centered.
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post #6 of 17 Old 12-16-2016, 04:05 PM
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they are not always "sideways" ...

They have been used either way. Here's one 'parallel" to the blade:


another:


Typically they are "sideways" or perpendicular to the blade. I think it may have to do with the actual bearing type itself. Some bearings take radial forces, others take axial forces better. There is more support to the blade with the bearing sideways than perpendicular.
I think the speeds would be the same, possibly less with the sideways orientation because of friction losses.


On the one I designed in college, I used the parallel approach:



The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #7 of 17 Old 12-16-2016, 04:24 PM
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deep groove ball bearings, as pictured in all of the above, do not tolerate much axial misalignment or much axial load.
there's a reason they are referred to as radial (deep groove) ball bearings.

there are ball bearings called "angular contact" that are designed to take axial thrust - but they only take thrust in one direction - so they'd have to be mounted in pairs behind the blade.

and as to twisting the blade to the point it runs off the width of the bearing, given the side bearings and distances involved, that's not going to happen.

but frankly methinks we need to define "side" and "parallel" because not much of the posts is making sense.
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post #8 of 17 Old 12-16-2016, 08:19 PM
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sideways vs parallel

It describes the plane of the bearing face. The face is the side where can see the bore hole. So, a bearing that is parallel to the blade's plane is shown in the photos. A bearing that is "sideways" or perpendicular to the blade's plane is the "WHY" part of the OP's question.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 12-16-2016 at 08:21 PM.
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post #9 of 17 Old 12-17-2016, 01:17 AM
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My bandsaw has the rear bearing guide so that the blade touches the outer race. Its quite common.
But many people do not fully understand how to set the rear bearing, which causes confusion.

Whichever direction the rear bearing is facing, the ONLY purpose of the rear bearing (guide) is to protect the teeth of the blade. Under no load running the blade should not touch the bearing at all. Once the side bearings (guides) are set so that about 1 3rd of the smooth blade is forward of them, then the rear bearing can be set at such a distance that when the blade is pushed backwards under load, the blade touches the rear bearing BEFORE the teeth get squeezed between the side blades.

Set too far forwards, and the blade twists and turns making people think the blade is blunt.
Set too far back, and the side bearings squash the teeth and then then blade IS blunt.
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post #10 of 17 Old 12-17-2016, 01:14 PM
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Quote:
Originally Posted by woodnthings View Post
It describes the plane of the bearing face. The face is the side where can see the bore hole. So, a bearing that is parallel to the blade's plane is shown in the photos. A bearing that is "sideways" or perpendicular to the blade's plane is the "WHY" part of the OP's question.
that's pretty much the impression I got - I've never seen a band saw with the blade set to run on the face of a bearing - either as a side guide or a rear thrust / steady guide.
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post #11 of 17 Old 12-17-2016, 02:48 PM
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there are some ....

Quote:
Originally Posted by TomCT2 View Post
that's pretty much the impression I got - I've never seen a band saw with the blade set to run on the face of a bearing - either as a side guide or a rear thrust / steady guide.
There are some that run on the face of the bearing:





The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #12 of 17 Old 12-17-2016, 03:50 PM
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I'd wager that part of it is contact points too. With the bearing running inline with the blade, you've only got the one very small contact point on the outer rim, whereas with the bearing sideways there's 2 contact points, top and bottom, so it should theoretically stabilize the blade better. Just a thought, I have no way to back that claim up.

The sideways bearing arrangement is also more compact, front to back. That could come into play as well

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post #13 of 17 Old 12-17-2016, 04:28 PM
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There is an old saying, "If it works don't fix it", many of us have used bandsaws for years with the stock arrangement with the perpendicular rear guide bearing.

Carter is an alternative solution, not all "experts" agree it is a necessary upgrade and would prefer to set the saw up so it tracks correctly so as not to have a problem in the first place.

The one exception is a parallel rear bearing with a slot in the face to use very narrow blades without side guides.
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post #14 of 17 Old 12-17-2016, 05:30 PM
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riding on the bearing face is a curious arrangement. no matter which way you cut it, that makes for sliding contact which produces / accelerates wear on the back / non-cutting edge of the blade.

mechanically it doesn't make the blade more stable - as the blade bows front-to-back due to (excess?) feed pressure the blade to brg face contact will be at the bottom of the top brg guide and the top of the bottom brg guide - i.e. still 'two point contact'

not so sure either arrangement is a short / lazy cut to blade tracking, tho. depending on an y kind / arrangement of a guide at the cutting height to keep the blade from tracking off the tires to the rear sounds like a problem in the making.

can someone point me to a newish make&model where I might find the set-up instructions on line?
there must be some reason/explanation/justification for one over the other.....

and getting to a prior post....what think ye of the Grizzly 14" 1 hp models - attractive pricing on their 75th model.....
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post #15 of 17 Old 12-17-2016, 06:14 PM
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I pretty much follow Alex's advice ......

The bandsaw setup video most often posted here:


More advice here EXCEPT it's in direct conflict with the one above?????

The "flutter test" for blade tension:

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 12-17-2016 at 06:30 PM.
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post #16 of 17 Old 12-17-2016, 07:07 PM
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conflict? what? there's more than one expert?
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post #17 of 17 Old 12-17-2016, 09:32 PM
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and getting to a prior post....what think ye of the Grizzly 14" 1 hp models - attractive pricing on their 75th model.....[/QUOTE]


I have the grizzly 17" 30th anniversary saw and love it. I've had it for a year or so and so far it's been a great saw.
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wish I had a cool line like everyone else...
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