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01-08-2011, 12:45 PM #1
Bandsaw blade not cutting straight....
Bandsaw blade not cutting straight....
Okay, the blade is dull, that I know. It cuts straight with a new/sharp blade.
So, the question is why does it always start cutting off in the same direction when it gets dull? On my vertical the direction is to the left from the operator position. Same on the horizontal.
Both these saws have rubber or urethane sleeves on the wheels. The side of the blade riding on the wheel is the side to which the cut veers when the blade gets dull.
It seem obvious to me, one side (edge) of the blade's cutting teeth must be getting dull faster than the other. I'm not sure which or why. Whatever the situation it's consistent, these are older saws and show evidence of the blade veering off from straight always in the same direction.
Any theories on why this happens? And, do your saws act in a similar way, consistently going off in the same direction, when the blade dulls?
01-08-2011, 01:53 PM #2
If the Vertical is a DoAll:
Check the Blade Guides, upper and lower. If the guides are not dead flat on the contacting surface the blade will wander after it wears.
I made a regrind fixture and new guides for the shops DoAll to keep the guides up to snuff.
The guides upper and lower need to be parallel. Readajust as needed so the blade does not have an induced deflection.
Look at the back-up bearing, the one the blade butts up against when the cut starts. Is it in good shape and is the 'cap' in good shape without grooves or a high shoulder?
Horizontal saws depend upon the guide roller bearings. The bearings must not be worn so that there is a drag on one side of the blade or the other. Like the guides in a vertical DoAll, the guide bearings must not induce a twist or deflection in the blade.
Are you getting a square cut with your parts? If the fixed jaw is not out of square then the bearings are not adjusted correctly.
An induced deflection or twist whether caused by worn guides, worn bearings, or misalignment will cause the teeth that help keep the blade tracking straight to wear prematurely.
01-08-2011, 02:07 PM #3
On the horizontal make sure coolant is flowing on both sides of the blade.
01-08-2011, 02:28 PM #4
After I wear down all the teeth on one side of the blade while trying to cheat and cut too tight a curve, yes.
If the blade is just dull, it will float between taking off to the left and taking off to the right.
01-08-2011, 02:29 PM #5
on my horizontal when the blade is pushing down with too much force and it's not cutting fast enough, it does not cut straight.
i will typically add force until it starts cutting at an angle then back offf. that maximizes my cutting speed.
01-08-2011, 04:11 PM #6
I have a Do-All 2013-V vertical bandsaw that I cut tons of plastic on. One of the plastics, a graphite filled polyimide, eats blades fast and when they dull, the blade always deflects away from the rollers (to the right when standing in front and cutting.) It has done this since the saw was brand new. I've assumed it was probably due to the rear roller bearing blade guide that the back of the blade runs on. It's positioned to the right, so the back of the blade is more likely to veer to the left, making the front go to the right. I've just lived with it so far, being careful to change out dull blades quickly.
01-08-2011, 04:29 PM #7
I have found bandsaws do not adide by laws of physics and have rewritten their own...
They cut straight when they shouldn't and cut crooked when they should... It all comes down tot he position of the sun and moon and what you ate a week ago for breakfast.
01-08-2011, 04:56 PM #8
Never have paid much attention on the vertical because I don't do a lot of cutting on it. But, on horizontal saws, every one I've ever used, regardless of whether it had ball bearing guides or solid carbide guides, would cut back in toward the vise as the blade went thru the stock once the blade is dull. I use a manual Wellsaw and an automatic Kalamazoo regularly now, and they both go the same direction when dull.
Also have one of the old 4x6's from back when they were made in Taiwan instead of China that I use with a 14T blade for cutting thin wall tubing and similar stuff. Blade gets dull, it goes the same direction.
In the past I've sawed miles of stacked angle iron on a Johnson. Blade went the same direction on it too when it got dull. And had a brand new 9 or 10 inch Do All in a shop I ran at one time that also headed off in the same direction. For some reason, we had poorer blade life on that Do All than on any other saw I've ever used with any regularity. I'd say either of my current saws will cut 5X as much stock before the blade is shot as compared to that Do All, with all of them using similar 1" wide variable pitch blades and cutting similar materials. Had Do All's service people in a couple times, and they never could come up with any reason for the poor blade life. Didn't matter whose blades we used either. It'd kill Do All, Starrett, Simonds, or Lenox with equal efficiency.
01-08-2011, 06:48 PM #9
I use Lenox Diemaster 2, 1/2" wide 6-10 blades and twice now I've come across bad batches of blades. I'll be sawing merrily along, then the blade gets dull (sawing the graphite filled stuff), switch to a new blade, and it's instantly dull within the first inch of cut. It took awhile to figure out the first time, but it was a bad batch of blades. Maybe they didn't harden the teeth at the right temp? I went through 3 new blades with them instantly being dull, then found a new blade with a different lot # printed on it and that blade worked great, so I sent back all blades with the bad lot #. This has now happened twice.
Does anybody make a 1/2" 6-10 tooth spacing blade with carbide teeth? When I do the unfilled polyimide material, there's virtually no blade wear, but when I switch to cutting the graphite filled material, the blades dull out after ~40-50 feet of cutting (range of thickness .25" - 1.5".)
01-08-2011, 10:28 PM #10
A fixture I made for grinding DoAll blade guides. I also made new guides out of 4140 and hardened them.
01-08-2011, 11:00 PM #11
I attribute most of my crooked cuts to running the blade too fast in harder materials without coolant. So I try not to do that
Following the blade manufacturer's instructions for breaking in a new blade may help prolong blade life. A new bandsaw blade will cut much faster than is good for itself. It doesn't know any better, so you have to hold it back You've got to give it time to lose a bit of that extreme 'new' sharpness in a uniform manner.
And of course, the blade needs to be perfectly perpendicular to the swivel axis of the saw as it will have the greatest tendency to follow that path regardless of where the guides point it. This may be a non issue on most saws because the relationship of the guides to the saw axle is probably fixed by the way it was built.
01-09-2011, 07:54 AM #12
I too have noticed on my horizontal saw the blade always starts veering toward the vice as it dulls.
My theory is this is based on how the blade is held by the saw. The blade guides twist the blade from the plane of the wheels to the plane of the cut. Forces are constantly trying to "untwist" the blade from the cut plane back to the wheel's plane. Thus as a blade dulls, it is trying to return to it's normal state, of not being twisted???
01-09-2011, 05:13 PM #13
all three of my horz bandsaws start cutting more on the vice side when the blades start going. I quit cutting anything over about 3" on the bandsaws and run all the big stuff thrue a 16" X16" peerless hacksaw. I can hold .015 all day on it, just ran 100 parts off of 6" Dia 4340 and then ran about 60 parts the next day in 8" Dia 6061 and it still will hold .015 with the same blade
Best part is the power hacksaw blades are dirt cheap on FEEBay
I`m still wundering why it is I can more parts with 6" of the power hacksaw blade than I can with 13' of blade on the auto saw.
01-09-2011, 06:14 PM #14
It sounds like the set might be gone from one side of the blade. If that happens, you'll never cut a straight line.