I know it occurs, but I realized last week I don't understand why. Assume the weld is straight. Then the circumference of the back of the blade will equal the circumference of the front (toothed) side. If the blade is centered on the tires, why on earth does it curve, causing drift?
-- Andy Barss
"Andrew Barss" wrote
Wide bandsaws (ie 3in and above) are tensioned to take into accound the difference between the circumference of the back and the toothed edge due to heating as the blade cuts. This seems to be hardly possible for narrower bands.
Stretch a wide elastic band between finger and thumb and apply pressure to an edge. The band will twist sideways, one way or the other.
I suspect that the only means of reliably getting a straight cut is a very sharp blade that applies minimal pressure to the edge of the band.
Jeff G
It could be a lot of things. Are your guides tight, and were they adjusted after the blade was set to track properly (i.e., withdrawn from the blade while adjusting tension and tracking)?
If the side guides have too much play, the blade will move around in the space between them. If the rear guide is too far forward or back, pressure against the front of the blade as you move the workpiece in will cause it to bow (or against the back of the blade if its riding hard on the rear guide), and the "outside the bow" edge of the blade will twist or wobble.
What you paid for it is what it's worth, and I made it all up. :)
er
"Andrew Barss" skrev i melding news:e24j15$cnh$ snipped-for-privacy@onion.ccit.arizona.edu...
I use a lot of softwood, like pine and fir, and the dust tends to build up between tyre and blade, probably causing most of the drift on my bandsaw.
There is a brush, but the resin from the wood is rather resistent to this, and if I do not scrape it off with a knife once in a while, I get a lot of vibration and noise.
BjarteR
There was a good program on DIY Woodworking about this subject. David Marks explained that the set on every bandsaw blade has different variations. The saw has to be tested and the fence adjusted to the true line of the blade cut every time a new blade is installed. Once the proper line/angle is established the blade will cut true. Bugs
It also has to do with the blades position on the tires. If you look at the tire edge on you'll see it's convex with a crown in the center. If the blade is running towards the back of the tire it's going to make the blade point to the right, because its on the back edge of this curve, whereas if it runs on the front of the tire the blade will run to the left. You can leave the fence parallel to the mitre slot if you use this to your advantage and simply use the upper tire adjustement set scew to counter any drift instead of moving the fence.
Besides the other answers, a dull blade will cause drift. Apparently one side of the blade cuts more aggressively than the other. Improper tension, guides improperly set, and the blade does stretch some when tensioned. Unless it stretches perfectly across its width the front and back may no longer be coplanar.
Wrong size (width) of blade for the thickness of material being cut? Too fast of feed?
Maybe for the resinous softwoods you could swap in a brush with stiffer bristles? I've been toying with the idea of installing a brush in mine. I thought a finger nail cleaning brush was the right size, but too stiff--but it might be just right for green/soft wood. That and a shoe brush cut to the same size for normal stock...
er
It's usually caused by the way the blade is sharpened and the teeth set. The geometry for the teeth on one side of the blade doesn't exactly match that of the teeth on the other side of the blade.
: "Andrew Barss" wrote
:> I know it occurs, but I realized last week I don't :> understand why. Assume the weld is straight. Then the :> circumference of the back of the blade will equal the :> circumference of the front (toothed) side. If the :> blade is centered on the tires, why on earth :> does it curve, causing drift?
: Wide bandsaws (ie 3in and above) are tensioned to take into accound the : difference between the circumference of the back and the toothed edge due to : heating as the blade cuts. This seems to be hardly possible for narrower : bands.
Every discussion I've seen for correcting blade drift starts with a cold blade, and cuts a few inches into a board. Surely that doesn't produce enough heat to greatly expand the leading edge?
: Stretch a wide elastic band between finger and thumb and apply pressure to : an edge. The band will twist sideways, one way or the other.
Sure, but rubber bands stretch when you apply pressure, much more than steel does, I would think.
-- Andy Barss
I think that is done with the intention of getting a bead on the drift in the blade for the purpose of adjusting the fence to match it. I could be wrong, but I don't believe it is done to address distortion caused by a heat gradient in the blade.
er
Uneven set of the teeth can do it.
Ding Ding Ding Finallly the right answer!
Dave
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Others answered the same and with other equally valid responses, and I think this one is the right answer for stable drift.
er
How about the difference in friction caused by the guides or the blade? Or the classic wire edge on one side from cutting the band free from the coil. Lots of folks abrade this away with a fine stone to help equalize.
Then there's the set on the teeth, grinding burr too ....
Enoch Root wrote: : Andrew Barss wrote: :> :> Every discussion I've seen for correcting blade drift starts with a cold :> blade, and cuts a few inches into a board. Surely that doesn't :> produce enough heat to greatly expand the leading edge?
: I think that is done with the intention of getting a bead on the drift : in the blade for the purpose of adjusting the fence to match it. I : could be wrong, but I don't believe it is done to address distortion : caused by a heat gradient in the blade.
Right. But it assumes that there is no distortion due to heat, which is what I was trying to say, counter to Jeff's suggestion.
-- Andy Barss
This is all horsesit. Use a sharp blade and keep theside irons in LIGT contact, not too much pressure from the back bearing and it will be fine. go slower.
Well I think the band saw blade and saw manufacturers seem to maybe have a better grasp that a dull blade will cause a blade to drift.
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