Bandsaw blade wandering!

[Tony Ward]

I have a theory! The general complaint about bandsaw blades is the "wandering" of the blade when attempting to cut in a straight line.

However this problem is not evident (no complaints) when using the bandsaw for cutting curved shapes.

Is this because the cutting edge (the sharp bits) is supported by that back of the blade (e.g. it rests on the bandsawn section)?

If so, should blades used for re-sawing (depth of cuts exceeding 10cm / (4") ) be wider (e.g. from cutting edge to back of blade) or be tapered from front to back (that is the back of the blade wider than the cutting edge)?

I probably should have patented this idea?

[Jim Becker]

Resaw blades are generally wider blades. They should also never be used for curved work--that will affect staightline accuracy over time. The wider blade (usually slightly thicker, too) can be more stable and when new should wander less. One Euro style saws where the teeth are off the wheel, they also tend to cut straighter longer as there isn't any way for the wheel to affect the set of the saw teeth on one side as contact under tension with the wheel would do on other saws.

That all said, you still need to determine what direction "straight" is for your particular saw with a given blade (Changing the blade will affect this) and then adjust your fence to suit. (or use a point-fence and make the adjustment as you are cutting down the line)

[Matt P]

Yes, maybe a point fence. I've also found that pushing the piece at a very uniform speed helps - usually very, very slow. I've found that it's worth the painstaking slowness to get a straight cut on my little 10" Craftsman saw.

[Bob Dodge]

Tony,

One of the best articles I've ever read regarding "drift", was written by Jim Cummins in Taunton Press' "Power-Saws and Planers". It's an excellent read. I believe the article is titled "The Little Blade that Could".

That article was written based on a one-year study by two engineers from Lenox, who examined "what causes drift".

They found that the leading edge of the blade gets hotter than the back of the blade, causing the front of the band to expand at a different rate. With the band longer at the front than the back, the blade tends to wobble side-to-side. They found that the best way to deal with that , was to simply apply suitable tension to the blade.

Now, Cummins tried this recommendation, and found that he could not properly tension his blade on a 14" Delta bandsaw, unless he set the tension-gauge to the 3/4" blade-tension setting. He was using a .025" thick 1/4" wide band, with 4-tpi "hook" profile. This tension-setting gave him the recommended 17-18,000 p.s.i. that he was looking for, and totally eliminated any trace of drift.

Now, those same engineers also stated that carbon-steel blades anneal and soften at 400 degrees, quickly losing their sharpness. When that happened, the typical user would push even harder into the blade, creating even more heat, causing more drift. Cummins chose a bi-metal blade for his article, because bi-metal blades anneal at 1200 degrees.

Jim demonstrated the result by standing a short 12" log "on end" on the saw-table, then feeding it into the blade. Once he reached the centre of the log, he rotated it and cut a perfect dowel out of the centre of that log. No drift, no barreling. Jim stated that the cut was so aggressive, that there was a tendancy to overfeed, so he recommended using a 6-tpi 1/4" blade, .025" thick, which also produced a finer surface.

Seems to me that Jim also recommended buying a blade 1" shorter than usual to account for length increase under tension.

Taunton Press "Power-Saws and Planers", ISBN 0-942391-83-7

[Tony Ward]

thank you to every one for your valued response.