The latest issue of Wood magazine has an article on tuning a bandsaw, and one thing in particular caught my attention. I have not seen this particular adjustment mentioned in discussions of blade tracking problems, but it seems to make sense:
The bandsaw blade must be exactly on the crown of the wheel tire for the blade to be parallel with a squared fence. My first question is why are the wheels made with a crown if it causes poor tracking? If this is the answer to tracking problems, why are there countless articles about resaw fences and adjusting the fence to be parallel with the cut line, etc. Seems to me you would just fiddle with the centering adjustment untill the blade cuts nice and straight with a squared up fence.
Another interesting recommendation in the article is that the blade tension be lower than the recommendation rather than higher. Usually bandsaw articles are suggesting very high tensions and stronger replacement tension springs, and so on.
I have no glaring problems with my 14″ Jet, but would certaining like to maximize its capability. Any thoughts on the above?
Replies
I'm sure someone will come along with a more detailed explanation as I have to get to work.
But.. the crown effect on the tires makes it easier to track according to the experts and occasionally need to be re-crowned. Yet, on some of your larger and commercial machines they use flat tire with tonque and groove tires (no gluing) and have no problems getting it to track if the wheels are balanced and co-planular. On blades wider than 1/2" on those machines the teeth are tracked so they are just forward of the front of the tire. On 1/2" or less, they track them to center of tire.
Tension equates to beam strength on a blade. Without proper beam strength a blade will tend to wander especially on thick cuts as in ripping very thick and slicing for veneer. Most tension gauges are not accurate and produce less tension than indicated by the gauge itself. Most smaller BS's don't have a rigid enough back frame and castings and a spring strong enough to really tension wide blades properly without flexing.
So.. don't ask me what they mean by tensioning under recommended tension. You can go under with general and less vigorous cuts as they are not as demanding as thicker cuts and pure accuracy is not a top priority, IMO. But running a 3/4" or over blade on precision cut veneer or accurate ripping with very thick stock requires proper beam strength and anything less will lead to in-efficiency and waste.
And of course, this is just how I view the world...
Regards...
SARGE..
Edited 8/23/2006 11:42 am ET by SARGEgrinder47
Is this in #171? I'm not seeing it.
forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
FG, I don't have it in front of me, but it is the Oct. '06 issue. I am puzzled as to why many articles I have read on the subject have not mentioned the crowned wheel to be the source of blade drift. The diagram that they show in the article that illustrates this seems to make good sense.
Handrubbed,
My Delta 14" seems to have no crown in its tires. My 12" Jet had crowned tires. I had to readjust the Jet every time a blade change had to be made. I can change blades on the Delta without making any tracking adjustment. All I have to do is reset blade guides & tension. Blades/belts tend to ride on the high point of a crowned wheel. I am not certain that it accounts for how the saws track. I can only relate my experience. Perhaps you should replace your tires with crownless ones.Cadiddlehopper
Thanks, I will check that out.
My 1999 Delta has crowned wheels, the urethane tires are flat but take on a slight crown from the wheels. I'm not sure about older Deltas, I'll look at my dads next time I'm over there, his is 50's vintage. Every Delta owner I've talked to has remarked on not having to reset the tracking after blade changes.
Since the house is on fire let us warm ourselves. ~Italian Proverb
While the crown on the wheels will affect the angle of the blade relative to the fence, the angle of the guides will also affect this angle.
Tension is a strange issue. You might compare the tension that breaks the largest saw blade that a bandsaw can hold to the tension required to cause a significant amount of deflection in the saw body. I suspect on a 14" Delta bandsaw with 6" riser, there is not significant deflection at the breaking point of a 3/4" saw blade.
As to why so much diverse advise: Most people are simply idiots.
The crown improves tracking by encouraging the band to stay on the center of the wheel. Adjusting the tracking on a crowned wheel can affect drift, but there are other factors involved.
Lots of internet "experts" encourage high tension. I've never found it necessary. A sharp, quality band is much more important.
If your machine is working well, there's little reason to mess with it. It wouldn't hurt to make sure the wheels are close to coplanar and the guides are all in good shape and properly adjusted. There are lots of "improvement" parts available from various catalogs but I recommend taking all of those with a big grain of salt.
Pete
Regarding crown, it helps blades stay in the center of the wheel. On my Hitachi resaw I can mount anything from 1/4" up to 3" wide blades on the crowned wheels. That said, it's not a necessity and lots of saws are made with flat wheels.
Cutting parallel to the fence is affected by 2 things - the position of the blade on the crown (as related to above) and also by the set of the saw's teeth. You could have a situation of a blade running on flat wheels that will still cut at an angle just because the sharpening and/or set is slightly off.
BTW, I hardly ever use the fence anyway. If at all, a single point fence.
DR
You want your blade to be centered on the wheels. If it runs to either side you will put strain on the whole saw and your blade will have a mind of it's own. Crowned tires allow the blade to run on the center of the wheel. They also lift the teeth from making contact with the tire and chewing it up. In essence, you want the center of the blade on the center of the wheel and the wheels centered to each other, this equalizes and balances everything. If your wheels are coplanar there usually isn't a need to adjust tracking unless a blade tensions a bit off center or you are making a radical change in blade width. Here is a page with a ton of links about bandsaws. Some work, others don't. The first place to start is always the owners manual.
Blade tension can be checked on small saws just by raising the guides and pushing the blade. You don't want it to move sideways more than about 1/4". Without a blade tension tool, you won't know how much tension is on the blade. The cut can tell you a lot and you often make adjustments for each blade accordingly.
When ripping, you may have to adjust for blade drift. This is done by marking a straight line on a scrap and cutting in half way. The angle the board is at on the table is how much you have to set your fence to compensate for the drift. Clamp a fence and make a test cut. If the outfeed end is drifting away from the fence, you move that end of the fence closer and vice versa.
You have to remember that woodworking machinery spans a wide variety of equipment. Sometimes information that is meant for something like a commercial bandsaw mill gets transposed to a small shop saw. There is a world of difference when you are tensioning a monster mill blade with hydraulics compared to a 1/4" blade, with a hand wheel, on a 14" saw. The principal is the same but a non-production small saw is much less critical.
http://www.laymar-crafts.co.uk/linkc.htm
Once again, really great help from all of you good folks. I will check out that web site, too. One thing I know that I can use is better quality bands. Surprisingly they are rather hard to find on the shelf. Looks like I might have to go to the net to ordersome. Woodcraft here probably has a few, too. I am automatically ruling out ones from Home Depot, Jet, Sears, etc.
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