Bandsaw Wheel Alignment


I have recently purchased an older (green) Jet 20 inch bandsaw and have started reconditioning it. (An absolutely awsome saw, but that is another story). Basicly I am replacing some worn belts and tires, as well as cleaning and aligning it, etc. I have Mark Duginske's book and have been following the advice in the book, but the book has raised some questions.
After testing the coplanerity of the saw I found the the upper wheel was slightly behind the lower wheel. This is a condition which Duginske says is common and can be corrected with a spacer washer behind the bearing on the upper wheel. I agree that this non-coplanarity is common, since I have seen it in other bandsaws such as my very cheep 14 inch clone. But, why does it always seems to be in the same direction with the upper wheel being further back than the lower wheel? That coincidence seems odd enough to me that I wonder if the saw manufacturers have have been doing it for some unknown reason.
Does anyone know if bandsaw manufacturers purposely build in this kind of offset into the alignment on purpose? If it is easy to adjust, why is it so common in saws and mostly in the same direction? What kind of advantage could it have? The blade tention does not seem capable of warping the wheels in this manner. This saw even has adjustments for tuning the position of the wheels, but they seem to have been purposely aligned with the wheels very parallel, but offset in depth.
I will probably try running the saw both as it is and with the wheels fully coplaner once I have the tires replaced and the saw put back together so I can see how much of a difference there is. However, I doubt I am experienced enough to notice much of a difference, and was wondering if anyone knew more about this common irregularity.
Inquireing minds want to know.
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tom saksa wrote:

advice. It seems to me that the Powermatic knows a hell of a lot more about band saw geometry than duginske. Other than that, the book had some useful tips.
I immediately removed the washer once I saw how poorly the blades tracked. I've been running a variety of blades from 3/16 to 5/8" on my PM and they all track beautifully. I don't really know what Duginske was thinking. Maybe some other brands/models need re-engineering??? (I doubt it, but not having messed around with any others, I'll leave that question for others to answer)
Dave
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David wrote:

Which powermatic do you have, and what do you think of it?
Chris
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Chris Friesen wrote:

Chris, I've got the 14" unit that is in current production with the flat belt, light, and sawdust blower (never sure what the proper term is for that tubing that blows the cut line clean). I LOVE it! It runs like the proverbial sewing machine, tracks perfectly. I like the guides, the tensioner, the height of the table, the dust collection. To me it is lightyears better than a Delta. I owned 2 Deltas and wouldn't' give you a nickel for either one. Being tall, I have no desire for the pricier BS's because their tables are so low (Laguna, etc). Besides, I don't really feel that spending more money would get me any big improvement over the Powermatic.
dave
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David wrote:

LOL.. I guessed you learned the lesson "If it works, don't mess with it". I bought Duginske's book as well with my first bandsaw, but the saw seemed to work pretty well, so I didn't want to risk any tweaking that might be hard to undo.. Same with my 2nd saw. It tracks about 98% perfectly.. I don't want to risk fooling with it and going down to 60% perfectly (and wasting a Saturday). It is a nice book though.
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bf wrote:

was already a well thought out band saw. Duginske needs to retract his whole damn treatise on wheel alignment. He talks a good game, but the actuality is that the saws are made (at least the PM) to track correctly as they come off the assembly line. You are right: if it isn't broke, don't "fix" it!
Dave
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Stop and think a moment. You track by pitching the top wheel. The bore from the factory is to compensate for average flex only - strength of materials. Tracking is still done by changing the pitch, where you can run out of correction authority on the odd blade if you're not set up co-planar at zero adjust.
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Any way you look at it, tweaking is going to have to happen, either now or later when you're in the middle of something and it stops working properly. Me, I prefer to partially tweak and learn a great deal of adjustability options right in the beginning. The machine is cleaner (assuming it isn't too covered with shipping grease) and if there is anything wrong with the machine, it's better to know sooner when you're still in the newbie customer stage and have some options available.
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wrote:

It may be that when full tension is applied the planarity can change, and would tend to bring the upper wheel forward. Just guessing though.
-Leuf
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wrote:

I don't think any manufacturer intentionally builds an offset but they do build a slight angle (small fraction of a degree) into the shaft bore. It is for the purpose of compensating for the deflection that occurs with blade tension and to facilitate tracking.
Frank

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I have found that you can coplane your upper and lower wheels but when you put tension on the blade it will not be in coplane. The solutition is to check the coplane after it has the tension applied and make the adjustment to bring it into coplane. It will track dead on. Check out thread below
http://groups.google.com/group/rec.woodworking/browse_frm/thread/91f56902d02eb7b4?hl=en
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sdppm wrote:

http://groups.google.com/group/rec.woodworking/browse_frm/thread/91f56902d02eb7b4?hl=en
tension and it still didn't track properly. I took out the shim, and it tracks perfectly. Like I said before, Powermatic knows a lot more about building a bandsaw properly than Duginske.
Dave
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David wrote:

Must be black magic.
er
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They know more about their design, that's for sure. Writing a book to detail general principles can't fit all the specifics.
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Thanks for the information. I have finished replacing the tire on the upper wheel which was the one in the worst condition and the saw is now tracking very well. I will replace the lower tire when I have more time. That tire is in better condition, and I found it quite time consuming to completly remove the tire, and properly clean all the glue, and rust from the first wheel, so replaceing that one can wait.
Since the saw is now tracking well I have very little desire to experiment further in wheel alighment. But this saw has made me question some of the conventional wisdom on aligning bandsaw wheels.
This saw has a massive frame and a huge tentioning spring. But even though it is capable of putting much more tention than needed on the blades I am using, the wheels shows no measureable deflection with a very highly tentioned 1 inch blade. I very much doubt that the non-coplanarity I observed in wheel alignment has anything to do with deflection, wear, or anything similar.
The saw also has three adjustments for the upper wheel. One has a handle, and is used to adjust tracking like my 14 inch saw, and two others that look as if they can be used to adjust wheel alignment (both twist, and coplanarity). They are locked in place and noted in the assembly diagram as "factory set, do not adjust".
It really seems like the saw was not manufactured or set accidentally to this degree of non-coplanerity. It appears to have been adjusted this way on purpose. For now I will assume that the folks that made the saw know best and will just enjoy having a well made tool.
Tom

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Duginske says that if the wheels are not coplanar (while under tension) beyond a certain degree, then it is probably not a good idea to try to make them track properly by adjusting the wheel angle, i.e. the tracking adjuster. This makes sense. If the wheels are way out of coplanar then you'll end up tilting the upper wheel a lot to get it to track properly. You'll have wheels that are not in the same plane and the top wheel tilted excessively to compensate.
I think it is essential to check the coplanarity only while the wheels are under tension. If not coplanar, then add the washer.
I added a height increase block (riser block) to my almost-new Delta 28-475X. Under tension the wheels were out of coplanar (top wheel too far back). Duginske's methods seemed to work for me: I added a washer and the wheels were in the same plane. I make small adjustments with the tracker adjustment as needed for different blades.
The original poster wonders why many band saws seem to have the same pattern of the top wheel being too far back. I'm just guessing, but I can imagine they are made this way intentionally because it is always easy to add a washer to the top wheel but much harder (impossible?) to move the top wheel back or make any adjustment to the bottom wheel.

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