Why does a bandsaw cut crooked? - Router Forums
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post #1 of 23 (permalink) Old 05-05-2018, 09:59 PM Thread Starter
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Default Why does a bandsaw cut crooked?

So I just discovered that bandsaws do not cut straight as a rule. I’m embarrassed to say I’ve had one for almost 3 years and used if a few times but not often enough to have learned this on my own. I have noticed at times I seemed to struggle to make it follow the line but I thought it was just my poor habits and lack of technique. Today I really noticed it bad though and I was trying hard to cut straight and push my piece through parallel to the edge of the platform. I was cutting out a star pattern and noticed anytime I kept the scrap cutoff to the right of the blade I could follow the line easily. If it was to the left it was a chore to hold it on the line. Well I admit I’m very bad to just not set the depth adjustment to match the thickness of stock. But even after I did that it still didn’t help.

Just now a google search turned up an article saying no band saw cuts straight. They all drift either left or right. It seems mine drifts left of the line as I push wood through it. As for resawing wood I found instructions for making a fence to match the angle the blade cuts at. But how does anyone just cut a pattern out freehand without a constant struggle? I feel like I’m twisting my blade (I literally am!).
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post #2 of 23 (permalink) Old 05-05-2018, 10:15 PM
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it's called drift...
dull blade...
unequal tooth set...
economy blade as in cheap...
guides not set correctly...
blade tension is off...
tires worn/loose...
bad wheel bearing(s)..
fence not parallel to the blade..

Snodgrass is hard to beat...
https://duckduckgo.com/?q=bandsaw+tu...ffsb&ia=videos
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post #3 of 23 (permalink) Old 05-05-2018, 10:38 PM
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This is called drift, and it can vary with each new blade. There are a variety of ways to handle it, but it starts with the way you set up the blade to the way it tracks on the tire, to not setting the bottom guides properly.

Start by watching the attached video. Alex Snodgrass shows how to properly set up the saw, and if you follow his method, you'll find much of the problem just goes away. Note that you will get recommendations to check and maybe even reset the wheels so they are co-planer. But Mr. Snodgrass says don't do it. The jigs the factory uses to set up the bottom wheel so it is perfectly parallel with the top wheel is heavy duty, milled steel, and YOU or I are unlikely to ever set it as well as it was in the factory. I have never touched the bottom wheel on any of the four bandsaws I've owned. It has NEVER been the problem.

But having the blade ride centered just behind the gullets between teeth makes a huge difference, as well as learning to set the blade tension properly. There are other factors that come into play, such as making sure the blade guides are set properly for the type of guides you have. Older guides and Carter style bearing type guides are not supposed to touch the blade, some newer styles use blocks that do contact the blade. There are guides above and below the table, and both need to be set properly, if one is off, it can deflect the blade. Normally the bearing behind the blade should not be in constant contact with the blade, except when you are pressing the work into the blade. If the back guide is actually touching the blade, it can deflect the blade and you get drift.

Start by watching the video a couple of times. Snodgrass is pretty much the acknowledged expert on band saw setup. Hope this helps.

Cheap blades are more likely to give you problems. I also use a stone (on a stick) to round over the back edge of all my blades, which removes any rough spots and makes blades run smoother. Don't overdo this, just a light treatment does the trick.

Wider blades run a bit better than narrow ones, high end blades are more expensive, but also generally run better. Might be the welds are better.

One more thing to check is to use a block of wood to check whether the table is 90 to the blade. You can check this with a transparent protracter, but making one cut with a wood block, then flipping it upside down, checking to see if the blade still fits in that slot. Many tables are adjustable and a good whack can throw them off.
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post #4 of 23 (permalink) Old 05-05-2018, 11:32 PM
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All of the above, plus speed of feeding. If you PUSH hard then the blade will wander. try the same cut again but feeding much much slower. You have to let the teeth clear the dust from the cut.
The google article saying all bandsaws drift was written by an idiot who has never been able set up a bandsaw properly.
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post #5 of 23 (permalink) Old 05-06-2018, 01:00 AM
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Quote:
Originally Posted by Duane Bledsoe View Post
So I just discovered that bandsaws do not cut straight as a rule. Iím embarrassed to say Iíve had one for almost 3 years and used if a few times but not often enough to have learned this on my own. I have noticed at times I seemed to struggle to make it follow the line but I thought it was just my poor habits and lack of technique. Today I really noticed it bad though and I was trying hard to cut straight and push my piece through parallel to the edge of the platform. I was cutting out a star pattern and noticed anytime I kept the scrap cutoff to the right of the blade I could follow the line easily. If it was to the left it was a chore to hold it on the line. Well I admit Iím very bad to just not set the depth adjustment to match the thickness of stock. But even after I did that it still didnít help.

Just now a google search turned up an article saying no band saw cuts straight. They all drift either left or right. It seems mine drifts left of the line as I push wood through it. As for resawing wood I found instructions for making a fence to match the angle the blade cuts at. But how does anyone just cut a pattern out freehand without a constant struggle? I feel like Iím twisting my blade (I literally am!).
It is the front of the blade, that is teeth, that cuts, not the site, not the fence. Therefore it is the teeth that determine the direction of the cut through your cutting piece - the drift. On small hobby blades, the teeth are pressed. You can get the precision grounded teeth blades but they are expensive. The teeth are usually pressed from left to right, as viewed from the top of the section through the blade. Therefore the kerf on the right-hand side of the blade is large than on the left, therefore the right site cuts more than left, therefore the "drift" is to the right.
Every blade has a different drift. Even blades cut from the same coil have different drift when welded into the band. Therefore with each new blade, you need to do a test cut to determine the drift and adjust your fence accordingly to the angle of the drift.
The above applies also to the scrollsaw blades except that you don't use a fence with the scroll saw and you adjust to the drift by hand.
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post #6 of 23 (permalink) Old 05-06-2018, 02:43 AM
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By a strange coincidence, I cut this only yesterday. It is a piece of white maple and i skimmed this off of a piece that was only 3" x 2" x 1/2" on the bandsaw (NOT a plane!) because it was easier than sanding the piece thinner.
My bandsaw is a 14" model using a 3/8" blade with 10 TPI. This isnt supposed to be for veneer cutting, and I use it to make my curved bandsaw boxes, and this blade is well used. The piece was held hard to the fence with a push stick.

The vernier gauge is showing 0.2 mm thickness, which is 0.00787402". I cant find a chart that goes that low to convert that back to fraction inches.

Dont tell me that ALL BANDSAWS DRIFT. Tell that idiot in google.
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post #7 of 23 (permalink) Old 05-06-2018, 07:24 AM
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[QUOTE= But how does anyone just cut a pattern out freehand without a constant struggle? I feel like Iím twisting my blade (I literally am!).[/QUOTE]

Do you mean a straight cut of an actual pattern? If trying to cut curves then the size of the blade is what really counts. It's nearly impossible to cut curves with a large blade. The smaller the better but then you have to consider the thickness of the wood as well as the HP of the saw.
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post #8 of 23 (permalink) Old 05-06-2018, 08:20 AM
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My simple advice, is if you are having trouble with your bandsaw,
1/ ditch the blade. It WILL be damaged and you will struglle without ever achieving a good cut.

2/ Many people do not understand how important the REAR bearing is. Its there solely to protect the teeth of the blade.

3/ Set the blade as per the snodgrass video on the top wheel with all the bearings well clear of the blade. That works for 99.999% of bandsaws.

4/ once you have set the side bearings to support at least half the blade, with the teeth well out front, set the rear bearings so that when you push back hard on the blade with your piece of wood, The teeth DO NOT slide between the side rollers. make sure the lower bearing is also set to stop the blade from moving too far back.
Thats what the rear bearings are for. If you run a bandsaw blade for 5 seconds with the teeth pushed back between the side rollers, you have scrapped the blade.

5/ SLOWLY SLOWLY on the feed rate. Watch the blade all the time. If the blade tries to twist while you are cutting a straight line, you are pushing too hard.

Thats it. all you need to know about bandsaw set up and straight cuts.
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post #9 of 23 (permalink) Old 05-06-2018, 10:41 AM
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I have a book and video by Gary Roginsky and I’ve watched the Snodgrass video a few times and neither have trouble with drift. In Gary’s video he cuts some thin veneer (1/8 or less) over 3 or 4 feet flawlessly. Setup like in the Snodgrass video is important as is a good blade. I read in Roginsky’s book that you should always have at least 3 teeth in the work at all times so you may need a few blades. More teeth mean smaller gullets to clear the sawdust and therefore slower feed speed and you have to watch getting a fine tooth blade hot too. If you get tension right and where the teeth sit on the crown of the wheels correct then if the saw is mechanically sound you should get a straight cut.

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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post #10 of 23 (permalink) Old 05-06-2018, 12:00 PM
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Quote:
Originally Posted by Cherryville Chuck View Post
I have a book and video by Gary Roginsky and Iíve watched the Snodgrass video a few times and neither have trouble with drift. In Garyís video he cuts some thin veneer (1/8 or less) over 3 or 4 feet flawlessly. Setup like in the Snodgrass video is important as is a good blade. I read in Roginskyís book that you should always have at least 3 teeth in the work at all times so you may need a few blades. More teeth mean smaller gullets to clear the sawdust and therefore slower feed speed and you have to watch getting a fine tooth blade hot too. If you get tension right and where the teeth sit on the crown of the wheels correct then if the saw is mechanically sound you should get a straight cut.
As Charles said, you have to avoid getting the blade hot - metal expands when it's hot, the blade will "stretch" and the tension will relax and you'll feel that you need more pressure to cut properly. More pressure, more heat - blade expands, tension loosens. A vicious circle.

I watched Alex Snodgrass put on his demo at the Woodworking Show here in Baltimore a few years back, same in person as he is on his videos. A master of the bandsaw, no question.
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