Bandsaw: Do we really need the thrust bearing?

[Susumu Mori]

Hi all,

Since I upgraded my Griz 14-inch to a Felder 20-inch bandsaw (FB510), I started a lot of resawing. Now it truly widens my woodworking capability and is quite a joy to use.

Anyway, I'm still learning how to use this larger bandsaw and resaw wide boards. I would appreciate if you could shed some lights on my experience here.

The first thing I did with this new BS is, of course, I measured drift. I didn't see any. If the fence is parallel to the table, I can get a veneer of consistent width. If I check the drift in the way Laguna explains in their website (cut a board little bit and adjust the fence angle such that the back end of the blade is in the middle of the kerf), the back of the blade is slightly tilted to the right, but I ignored it.

Now, here is the interesting part. If I observe how the blade behaves very carefully during resaw, as soon as the blade is pushed against the thrust bearing (and the bearing starts to turn), the back of the blade is deflected to the left and sometimes touches the wood at the left side of the kerf, leaving some dark mark coming from the blade (maybe I should clean the blade). This is sort of understandable because as the blade is pushed against the thrust bearing, it has to deflect to the right or the left. I think that's natural.

Maybe the side bearings are suppose to catch the deflection and move it back to straight. My Laguna 1" ResawKing has 0.04-inch kerf. So, I'm talking about 0.02 inch of deflection. Because the Euro-style side bearings are slightly toe-in (narrower in the front and wider in the back), it doesn't prevent the deflection (according to MiniMax bandsaw manual, this toe-in configuration is intended, probably to enhance the bearing rotation).

The most puzzling thing is, if I do not use the thrust bearing, the bandsaw still cuts just fine. It is less nosier because the blade makes a shrieking noise as it scratches the thrust bearing. also, the kerf becomes slightly thinner probably because there is less force to tilt the blade. That's all I noticed. The veneer came out just fine.

OK, I just tested using a 6-inch board. Things could be different with a 10-inch board.

But if I think about it, I'm not sure if it is a good idea to push a BS blade to the bearing. The fact that the flexible blade is deformed to reach the bearing means, it is likely to keep finding a direction to deform after pushed against the bearing, right? OK, if there is no thrust bearing and we push too much, the blade may come out the tires. If that is the role of the thrust bearing, I would just set it maybe 1/8 behind the blade and as soon as I hear the blade touching, I slow down a bit. At least, I'm not sure why the bearing has to be right behind the blade.

If there is a reason that the thrust bearing really need to support the back of the blade during the cut, I guess the Carter-type bearing with a groove may make a sense. Or Laguna-type side support that keeps the entire blade length straight sounds a good idea. But if everything goes well without it, that sounds a good solution too.

In any case, if you could give me any advises, suggestions, or experiences, I would really appreciate it.

[Jerry Thompson]

Go to YouTube and enter Alex Snodgrass, do as he demonstrates. Yes you need the thrust bearing and when the saw is set up correctly there is no drift.

[Susumu Mori]

Thanks Jerry.

Yes, the video was very informative. He actually said if the thrust bearing is touching the blade without any load, it would deflect the blade right or left. I'm not sure why the deflection doesn't happen during the cutting as the blade is pushed against the thrust bearing. Anyway, in my case, the blade tilts as it is pushed against the bearing but the veneer comes out fine. If the blade were clean and didn't leave the mark, I might have not noticed, but I guess as the loading to the blade is not always perfectly constant and the blade tilt angle wobbles ever so slightly during the cut, it causes the usual bandsaw ripple marks on the surface....

[Andrew Hughes]

Too many things that affect the cut type of wood thickness .TPI When I get my resaw machine cutting good I just leave it alone till the blade get dull, starts building a lot of pitch.Or changing the wood from soft to hard.
then I pull the blade blow out the dust clean the tires a bit.And tension a freshly sharpened blade.I keep a 1, 3,4 TPI and a woodmaster Ct.I don't really notice drift unless the blade is going south.I have Aggi B20/20.
I also round the back of the blade slightly.I know it doesn't answer your question but hope it helps?Aj

[David Kumm]

If the saw is stout enough to tension the blade tight enough you seldom will use the thrust bearing. I run blades from 1/4" to 1" at 25000-30000 and only touch the bearing when pushing 12" wide boards. Makes the blades last longer too. If your saw won't tension as high the bearings become much more important. The stiffer the saw the less necessary it is to use the guides. Dave

[Susumu Mori]

Thanks Andrew and David,

Yes, now I suspect the blade tension plays a large role.
There is a nice description here (http://woodgears.ca/bandsaw/resaw.html), which exactly explains the blade deflection I experienced.
According to this, and also as suggested by David, the culprit could be the tension. I have tensioned the blade conservatively. My resaw has been great for up to 4-6 inches. For 8 inches and more, maybe I need to crank up the tension. I'll test it today.

[Jamie Buxton]

A brand-new blade depends less on the support from the thrust bearing. However, as the blade dulls, it needs more force to push it into the wood, and the thrust bearing can help with that.

[Jim Finn]

I use my GO555 to re-saw a lot of cedar, maple and some oak. Plenty of tension and a sharp blade and the thrust bearing seldom is necessary as long as I do not try to feed the wood too fast. Sharp blade is vital! I use a re-saw fence to re-saw 8" wood and get zero drift (with a new sharp re-saw blade)

[Susumu Mori]

Thank you all.
Today, I was resawing whole day to find a correct setup and seem to get it right. Now the back side of the blade stay put and doesn't touch either side of the kerf. The resaw face is clean. Only when I change the feeding rate a lot (like stop pushing), it leaves a noticeable ridge, but I guess it's normal. I'm not sure what exactly the reason but these seemed to have the most impact;

1) I found that the saw blade was a bit too much to the front of the upper wheel. I have read articles that the position of the blade on the upper wheel influences the orientation of the blade deflection, or drift (not sure whether these are the same thing). Because Euro-type BS has a flat tire, I thought the position of the blade on the tire was not very critical. Some say the blade tip has to be the center of the wheel while Felder/Minimax say the blade tip has to stick out from the wheel to protect the tire. I found the blade in my BS was shifted too much to the front. I don't know why it shifted since I initially set up the BS a month ago. So, I re-adjusted the position toward the back. Now the carbide tip is barely sticking out.
2) I increased the tension. My ResawKing is 1" and now the scale is a bit beyond 1".
3) I found the Felder manual recommends 3mm between the blade back and the thrust bearing. This is much wider than what I read in Internet. In my saw, it used to be right behind the blade. So, I pushed the bearing few mm back.

Now, the saw still reaches the thrust bearing and makes it turns, but I can feel that the saw is cutting mostly by its own tension, rather than pushed by the bearing from the back. I can see the back end of the blade flutters very slightly during the cut, but it is no longer deflected to the left. The effect of the stabilized blade is immediately clear while I'm pushing a wide board.

BS is surely an interesting creature.

Thank you all for your suggestions and advises!

[Alan Bienlein]

I didn't need the upper thrust or guide bearings while I was re-sawing this quilted mahogany. The piece in the picture is 16" wide and I've done up to 18" on this same band saw. This saw only has just over 12" re-saw capacity with the upper guides in place which is a waste as it can easily cut up to the max height of 18" clearance that it has with the upper guides removed.
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[Susumu Mori]

Wow! That's impressive.
As I get more experienced with my larger BS, I start to believe the fundamental factors (saw itself, blade quality and its width, tension, and blade position) are more important than the blade guides. This is what other members here have been saying all along and I start to understand it. Try to fix the problem by tweaking the guides seems a poor solution. You just proved it. Now my thrust bearing gently supports the back of the blade and the side bearings only occasionally turns. I have less shrieking sounds from the thrust bearing. Most importantly, the cuts are clean. Thanks for the advises.

Alan, by the way, you are using a short fence for such a tall board. Do you use your eyesight to make sure the even board width (especially at the top of the board) or you just rely on the pressure against the fence?

[Alan Bienlein]

I run the edge on the jointer to square it to the face. I then set the fence and make sure it's face is square to the surface of the cast iron top. The fence itself is set parallel to the miter slot. I do run a pencil line on the top and both ends just for reference during the cut but I keep pressure against the fence while cutting.

I think people get into trouble using short fences like this for tall pieces because they try and push from the top where it is unsupported. The pieces I cut like this will stand upright by themselves which makes them very stable due to the fact I make sure the edge running on the cast iron top is flat and square to the surface against the fence.

[John TenEyck]

Others may do it w/o problems, but I would NOT remove the blade guides. You are just asking for the blade to get thrown off the back of the tires if anything goes wrong. Best case, nothing happens except you ruin the blade. Worst case, you get to see the inner workings of an ER.

When all else fails, read and follow the owner's manual.

John

[Alan Bienlein]

I have also done this on my G0555. I didn't want the riser when I bought it and needed to re=saw a piece that was just over 7" wide so I removed the upper blade guides and went at it. I can do just over 8" this way since I trimmed the bottom of the upper door.
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[Phil Thien]

Others may do it w/o problems, but I would NOT remove the blade guides. You are just asking for the blade to get thrown off the back of the tires if anything goes wrong. Best case, nothing happens except you ruin the blade. Worst case, you get to see the inner workings of an ER.

When all else fails, read and follow the owner's manual.

John

Typically there are still lower guides (below the table) that will prevent the blade from coming off the wheel.

And blades coming off wheels (breaking, etc.) tend to be pretty anticlimactic. The teeth tend to catch on the frame of the saw and the blade comes to a stop in pretty short order.