Advice before I put on riser block? (Coplanar attempt too...)

[Bay Area Dave]

Michael, you set yours up the way YOU want, and rest assured that my Powermatic works best as it came from the factory.

dave

Michael Daly wrote:

[Stephen M]

Good. I glad we have found some common ground. Particularly sice we have been called "children".

Woodtek 18"

FWIW I ran the numbers and I was surprised by some of the numbers for My saw:

The wheel is 1-3/8 the tire is actually 1-1/4. The crown is about 3/32 The distance between axels is about 44"

From that, I calculated that the radius of the crown is a shockingly small

2.95" (lets call that 'r').

Lets suggest more modest 1/8th" blade shift. That means that at 1r (about

3") below the a upper axel the blade would pas back across plane defined by the upper wheel.

For each r thereafter, it would be 1/8th" back in the opposite direction from the shift.

44"/r -r = 13-2/3r 1/8" * 13-2/3 = 1.7" (my *calculted* coplaner fudge factor)

Adjustments for reality:

The crown is on my tires appears to be more like a triange than an arc this would tend to increase the fudge factor. The tires are mushy, This would tend to decrease the fudge factor.

I'll bet that the later has more impact. than the former. This supports my hypothesis that the fudge factor allowed by the crown on *my* BS is > the tolerances of even a half-assed manufacturing process.

I will aknowledge that the mushy tire factor makes this rather less than perfect, but at least lets us get our arms around the order of magnitude to which crowning can help mitigate a non-coplaner situation.

What practical lessons can we learn from this excercise?

I think it's clear that less crown makes a saw more vulnerable to non-coplaner issues causing a tracking problem. So if you have a "situation", shim if you can, but if you have old tires, replacing or recrowning *may* help considerably.

-Steve

[Rick Chamberlain]

We're not talking about a precision cutting machine here Mike. But, in any event, I'll try to sum it up with an analogy.

Being an engineer, I'm sure you know that older cars had points that required adjustment in order for the engines to run properly. I remember an old Mustang I worked on in high school - I could never get that thing running quite right. Did everything by the book - points were perfect, timing was perfect, vacuum advance was perfect, all according to the book.

When I asked the instructor what could be wrong, he said that sometimes you start with the factory settings and tune according to feel. Once I figured out what he meant, I adjusted the points and timing a bit and that Mustang purred.

Same thing for a bandsaw. The problem with most bandsaws is that you can't state a blanket "no more than 1/8" out of coplanar", because of manufacturing issues - cast or sheet metal frame, single or double wall construction, aluminum or cast wheels, rubber or urethane tires, size of crown, type of bearing, etc.

Most hobbyists don't really care about the fatigue on a band, as we don't use our tools in a production environment, and if they read all the books by Duginske, they already know to detension the band after use. I would say that most hobbyists are more concerned about performance, and in my case that is all I care about. My bandsaw is close to 50 years old - a sheet metal framed Delta 20" with new bearings, tires, even paint. No matter what band I use on her, she's a bit outta whack. I could shim and check, shim and check, shim and check. Or, I can leave well enough alone and cut wood.

I don't have a newer bandsaw to compare to, so I have no idea how much out of factory spec the new Deltas, Jets, or Lagunas might be.

Is Duginske wrong? Not necessarily. But is perfectly coplanar necessary for a well tuned 67 Mustang? I'll leave it to you to decide.

[Michael Daly]

Something I knew intuitively, especially since my BS has flattish tires (certainly compared to yours). Watching the behavior of mine without covers on, with different degrees of co-planar and tracking makes it easy to agree.

Good advice. Certainly more useful that "coplanar is a myth". It also points back to the issue that folks with high-quality bandsaws that come well set up from the factory shouldn't be giving off-hand advice to the rest of the world.

This has been a useful discussion, I think.

Mike

[Michael Daly]

I think that unless the bandsaw is a real loser, the only significant issue is tire type and geometry.

That's entirely possible. However, I keep it in the realm of the possible that for some situations, fatigue _might_ reduce the life of the blade. Without doing some calcs, I don't know. However, the conservative engineer part of me says "do it right and don't even consider the possibility." Setting up a bandsaw is not hard, so don't make an issue of _not_ setting it up right.

I've already said that perfect is not possible, but "good enough" is. "Coplanar is a myth" doesn't even address good enough. Since making the bandsaw reasonably coplanar is straightforward, do it and if you're still having problems, you know to look elsewhere for a solution.

Mike

[Rick Chamberlain]

Steve,

There is no doubt that recrowning *does* help considerably. It's not a hypothesis, it is fact.

In a prior life I worked as a pinsetter mechanic. The mechanism used to send bowling balls back to the bowler is called the accelerator. Nothing but a large flat belt riding on two crowned pulleys (kinda like a bandsaur) with a ramp underneath. The ball gets caught in the ramp, the belt stretches as the ball climbs the ramp, and at the end of the ramp the ball comes out at about 15-20 mph. Can you imagine what happens when the crown on those pulleys wears down? No adjustment in the world would keep those belts in place, and you can adjust the pulleys front to back and left to right.

But, put new pulleys in there, and you could be so far OOW (out of whack) on the coplanar thing and the belt would track properly with no adverse effects, regardless of belt wear or adjustments made to the pulleys.

Both you and Mike are missing the point here. You're working so hard to calculate the OOC (out of coplanar) factor and the fudge factor that you've not addressed what the manufacturers say are acceptable levels of OOC. Nor do you address the fact that bands may actually *require* an OOC condition to run properly.

I've not found anyone here say that a severe OOC condition shouldn't be considered a drawback, or if one appears on a new bandsaw that it should not be addressed by the manufacturer's warranty. But there is a whole lot of information from a whole lot of knowledgeable folk here to support "coplanar is a myth". I guess I'd rather be cutting wood instead of fretting over a 1/8" deflection in my BS blade, especially since I don't know if that 120" blade is 100% true to begin with.

See my previous post about the 67 Mustang if you don't get it.

[Michael Daly]

On the contrary - I've specifically asked for any info that would define what an acceptable ooc would be. No one has come forward with any useful information with the exception of Steve (who's sort of working from first principles).

I can't remember seeing anything of the sort. Can you give a reference to a post by one of the coplanar is a myth crowd that actually does address this?

Mike

[Rick Chamberlain]

If you mean geometry of the crown, I'd agree. The problem with geometry is dealing with a particular band or tensioning device/spring. A 1/8" band on my 20" Delta may require the upper wheel to be at a severe angle, thus negating or accentuating the OOC (out of coplanar) condition. OTOH, a 1" resaw blade requires so much tension that the wheel could be forced true.

In these cases, geometry is directly affected by the size, type, and material construction of the band - not to mention the weld/solder joint, which could open up another can of worms...

Agreed. But just what is *right*? There is clinical right, which is probably close to what you espouse. There is functional right, which is more of a gray area and works on the premise of feel instead of original spec. In reality, no one is wrong. I use the book as a starting point. If it works, I leave it. If it doesn't, I tune it according to common sense and feel. Am I "more right" than you? I don't really care, but my way works for me.

Agreed, but aren't you contradicting yourself a bit here? First thing I learned as a network engineer is that similar is spelled "different". Reasonably coplanar is not coplanar, therefore "coplanar is a myth" is technically correct. :-)

[Rick Chamberlain]

You've asked this group, but have you asked the manufacturers? IOW, Delta may say that 1/2" OOC is ok, while Jet says 1".

Not sure how to do this Mike - sorta like proving a negative. :-)

[Michael Daly]

No, it's proving a positive. Just DAGS on this ng and find a post by one of the naysayers showing that they actually address the severe ooc condition. I only remember them saying, bluntly and unconditionally, that it's a myth and ignore it.

Mike

[Michael Daly]

That sounds right to me - the starting point is a coplanar bandsaw. I haven't argued for anything else. Screwing around with a wildly ooc bandsaw is a good way to waste a lot of time.

Splitting hairs isn't going to solve anyone's problems. If making it coplanar requires a gazzillion dollar widget and several days to get it perfect, there's a perfectly reasonable expectation that folks will balk. However, using a straightedge and aligning it accordingly is a reasonable attempt at making it coplanar. If you're still out by 1/8" or more, then you probably shouldn't be using a bandsaw.

Mike

[Bay Area Dave]

You aren't by any chance the fellow that goes by George Preddy in the digital photo NG are you? He is a Foveon fanatic who's posted OVER 3,500 posts on the merits of that sensor over Bayer sensors which are used in Canons, et al. This coplanar thing is gonna become your legacy.

Go have a beer and relax, Michael...

dave

Michael Daly wrote:

[bridger]

well, I for one have on more than one occasion fixed a bandsaw that was throwing bands by aligning the wheels....

[Michael Daly]

Beats having your reputation, BAD boy.

Mike

[Bay Area Dave]

I'm not so sure about that. I must have SOME entertainment value; witness the undo attention I receive from the likes (or more to the point, the ilk) of TW.

dave

Michael Daly wrote:

[Tom Watson]

cf: "whack-a-mole".

cf: "plagues of egypt".

cf: "children of israel".

cf: "kant tried to determine a rational basis for the inclusion of irrational beings into the polis - he was unsuccessful". (op cit ref JOlP, v. 4, Letter 12.3).

cf: "turds float".

Thomas J. Watson-Cabinetmaker (ret) Real Email is: tjwatson1ATcomcastDOTnet Website:

[Bay Area Dave]

did you notice I said my hard drive crashed and I'm starting up the filtering again. you aren't on it yet, buddy boy.

dave

Tom Wats> >

[Rick Chamberlain]

No doubt - I'm sure everyone would prefer to start off with a pristine bandsaw within all MFG tolerances. In reality, probably ain't gonna happen.

Mike, isn't splitting hairs what engineers do? :-) I tried to point out the contradictory choice of words. Similar *does* actually mean different, doesn't it?

[Stephen M]

Um, no.

Mike, as a digital professional (I R 1), sometimes it's it easy to forget the leave the discrete world or 1's and 0's and return to the real (in the mathematical sense) world. There is no such thing in the real world as straight, flat, perpendicular, flat or coplaner. If you think it is, then you need a better measuring tool. Even light bends.

Common usage of "straight" really means "straight enough" or "relatively straight". The same thing goes for "coplanar".

I would submit that in the context of woodworking, "similar" at least as often as not *does* mean "same".

As a "software engineer", I am invoking the right bestowed upon me by my employer and the State (University) of New York, to split that baby right down to the follicle :-)

-Steve

[Rick Chamberlain]

Steve,

I think you made my point. :-)