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Blade tracking problem

 

John,
Following your suggestions, I loosened/removed the blade and zeroed the upper wheel, laying a straight edge across it to monitor the tilt as I adjusted the tracking mechanism.? Then I re-tensioned and adjusted until the blade was just above the rim flange.? The blade still was misaligned enough to scrape the guard.? I noticed that tightening the mechanism's center bolt also affected the tracking so I used an interative approach -- adjust the bottom screw, tighten the center screw, check the tracking, loosen it and re-adjust the bottom one, and so on.

FYI, I became curious about how much the frame itself is bending on that axis.? I didn't expect much, but what the heck.? I again used my laser pointer, attaching it to the top of the frame and aimed it down.? There is a lip near the bottom where I could place a machinist ruler to check the deflection.? From no-tension to fully tensioned, the beam deflection was pretty small -- something on the order of .02 inch, .5mm.? ?I just realized that this could be a way to set the blade tension.....with some characterization, anyway.

I also loosened up the blade guides and found that worsened the tracking problem.? Moving the bottom blade guide down also exacerbated the tracking problem.

Other than fooling around with the tracking mechanism and blade guides, I haven't modified the band saw.

The blade isn't the newest in the world, although it is NOT the one that came with the saw -- not long after getting the saw I got a bimetal blade for it.? If the problem is (somehow) related to the blade, would there be any other symptoms to look for?
 

Yep that iterative approach (loosen adjust re-tighten) is necessary, and yes the spring-bending of the frame can be used to set the tension - but there is the same old problem - you have to know what full tension IS before its any use.

Having a blade that you know tracks properly is a sort of given when adjusting tracking, like knowing how to adjust to full tension. Couple things to try:
1. Blades not welded square don't track truely?and would cause the problem you?describe. Probably something everyone should do first, when trying to solve tracking problems, is try a new blade. If it cures the problem you're ahead of the game, if not, you know it's?not the blade and you've?got a?good spare.
2. If the blade was cracked it would track away from the rim. You can test this out by cutting a piece of steel at full (8lb) bow weight - if the blade is cracked the head will bob up and down as the crack passes over the rear support rollers.
Not well known, but the blades crack just by running them enough around the standard bandwheels - even without?guides twisting it, a blade will only last from?20-50hrs. Possibly yours is cracked????
I'll keep thinking - jv



On Mon, Feb 21, 2022 at 11:21 AM Mark Kimball <markkimball51@...> wrote:
John,
Following your suggestions, I loosened/removed the blade and zeroed the upper wheel, laying a straight edge across it to monitor the tilt as I adjusted the tracking mechanism.? Then I re-tensioned and adjusted until the blade was just above the rim flange.? The blade still was misaligned enough to scrape the guard.? I noticed that tightening the mechanism's center bolt also affected the tracking so I used an interative approach -- adjust the bottom screw, tighten the center screw, check the tracking, loosen it and re-adjust the bottom one, and so on.

FYI, I became curious about how much the frame itself is bending on that axis.? I didn't expect much, but what the heck.? I again used my laser pointer, attaching it to the top of the frame and aimed it down.? There is a lip near the bottom where I could place a machinist ruler to check the deflection.? From no-tension to fully tensioned, the beam deflection was pretty small -- something on the order of .02 inch, .5mm.? ?I just realized that this could be a way to set the blade tension.....with some characterization, anyway.

I also loosened up the blade guides and found that worsened the tracking problem.? Moving the bottom blade guide down also exacerbated the tracking problem.

Other than fooling around with the tracking mechanism and blade guides, I haven't modified the band saw.

The blade isn't the newest in the world, although it is NOT the one that came with the saw -- not long after getting the saw I got a bimetal blade for it.? If the problem is (somehow) related to the blade, would there be any other symptoms to look for?

 

My blade might have upwards of 20 hours on it so a relatively simple thing to do is buy a new one and see how it behaves.? I do see the frame bob up & down but it _appears_ to be associated with the weld.? I'll see if I can mark that location to see if it correlates to the bobble.

I'm starting to understand that bandsaws have more components that affect their performance compared to your average (manual) lathe or mill.? They're overlooked because they usually are just used for the first step in machining something -- i.e., cut stock so it can be further processed by something else.? Fortunately they're not expected to be highly precise, but it IS a time-saver (and material-saver) if the cuts are reasonably accurate.
Mark
 

Today I was cutting a 3.25" diameter piece of aluminum on the bandsaw and keeping a close eye on it, to see if the "bobble" corresponded to the weld on the blade.? I noticed it was getting worse and worse so I turned the saw off immediately after the frame jumped, then examined the blade.? It has a crack extending almost halfway across the blade.? So John's comment was dead-on.

Time to get myself another blade or two.....

Mark
 

On 2/22/2022 6:11 PM, Mark Kimball wrote:
Today I was cutting a 3.25" diameter piece of aluminum on the bandsaw and keeping a close eye on it, to see if the "bobble" corresponded to the weld on the blade.? I noticed it was getting worse and worse so I turned the saw off immediately after the frame jumped, then examined the blade.? It has a crack extending almost halfway across the blade.? So John's comment was dead-on.
Time to get myself another blade or two.....
Mark

Check out the guys at lacuttingproducts.com . I've been buying their stuff for a while now , good products at a decent price . Get on their email list for some pretty decent discounts from time to time . I think MAGLA5 is still good for 5% .
--
Snag
My rights don't end
where your fears begin.
 

Yes, lacutting products is one of the sources I found on Amazon and ebay.? Their bi-metal blades actually are slightly lower priced than Harbor Freight's bi-metal bandsaw blades.? There are a bunch of Chinese-made blades that are cheaper but I'll support a US-based company.

Thanks for the discount code!

Mark
 

Good to know something worked. Not proven yet that it IS your tracking problem until you try the new blade
You said you cut mostly Aluminium. For this there is no point in using a bimetal blade.
Bimetal blades are useful to cut steel on high speed? and at high bow weight where the cutting edge can get hot enough to dull a carbon steel blade but Al conducts heat so fast the edge never gets near the temp needed (5-600F).?
?Quickest and straightest cutting of bulk soft materials like Al is to use a 4 or 6 tpi blade and Carbon steel cuts just as fast as bimetal in soft stuff.?
Do your wallet a favour and get a 4tpi blade for the 2"+thickness and an 8 or 10tpi blade for thinner stuff.
The normal 10-14 bimetal blade as actually too fine for any aluminium other than thin section.?
You never really want more than about 6 teeth in a cut in Al because the swarf sticks in the gullet of smaller teeth and either makes it cut vertically crooked, or jams the blade in the cut (stalling the motor and possibly burning it out) - jv

On Wed, 23 Feb 2022, 1:11 pm Mark Kimball, <markkimball51@...> wrote:
Today I was cutting a 3.25" diameter piece of aluminum on the bandsaw and keeping a close eye on it, to see if the "bobble" corresponded to the weld on the blade.? I noticed it was getting worse and worse so I turned the saw off immediately after the frame jumped, then examined the blade.? It has a crack extending almost halfway across the blade.? So John's comment was dead-on.

Time to get myself another blade or two.....

Mark

 

On Sun, Feb 20, 2022 at 02:05 PM, John Vreede wrote:
Then the bottom wheel is moved in or out on the drive shaft to get it to also track <0.040" from its rim.? You do this by changing the length of the spacer between the bottom wheel and the gearbox out bearing.
?

This is excellent information. I have a new saw (actually over a year old now) with some discrepancy between the ledge of the upper and lower wheels. if I remember right it's about .030" further out on the lower wheel and in my opinion it's not enough to worry about. I remember thinking the only way to fix this would be to move a wheel in or out but I wasn't really sure which wheel.?

I have something to add about blade tracking that is worth looking at. When I got my saw it seemed like everything was set up and ready to go so I started using it without making any adjustments. Then I started increasing the weight (it was cutting very slow) and as a result the blade started falling off. Most often this mutilated the blade and made it unusable. After the third blade I realized I needed to take a closer look. I found what I thought was the problem and then confirmed this with other saw manufactures.

First, (as you said John) the blade tracking need to be set with the blade guides removed. Then when the guides are installed they should twist the blade along the center line without deflecting downward or to the left or right. Ideally the bearings in the guide should only contact the back of the blade while cutting although it needs to just barely kiss the bearing all the time. Very slight pressure is also fine.?

The problem on my saw was that the blade guides were deflecting the blade downward nearly 3/8". With the guides set correctly the saw would not cut deep enough. The cover near the top wheel hit the base. Even when I removed blade cover the upper frame hit the switch housing before completing the cut. After doing a little research I realized my saw was defective. I looked at two other older saws that did not have this issue. I suspect this problem is a result of a bad setup at the factory. Maybe the pivot point for the head was not located correctly. In reality the pivot point on my saw needs to be dropped over 1/4".?

I ended up putting a 1/4" steel plate under my vise. This elevating plate raises the stock enough so that the blade can complete the cut without being deflected significantly by the blade guides. Since making this change I can increase the downward pressure to full. Sometimes the saw stalls but the blade never comes off. In fact, I have had the same blade on my saw almost a year now. It has cut a LOT of steel.?

I had a bunch of these elevating plates made (laser cut) and have sold over 60 of them (apparently quite a few saws have this defect). I currently have one plate in stock but if there's enough interest I can have some more made. When the price of steel went nuts I raised the price from $29.50 to $39.50 but honestly it's barely worth my effort. After the cost of steel, laser cutting and shipping I'm about $2 ahead. Let me know if your saw needs this plate. If there is enough interest I'll have more made.?

Mark

https://markq6zlmc.fws.store/Elevating_Plate/p7671236_21023715.aspx
 

Hi all
It's actually quite astounding that there are so many faults with these saws, and it's not?just one brand, it's all? of them. If they were making lathes no-one would buy them!??
Part of the problem is that there are so many adjustments that almost anything can be MADE to cut, but when it comes to cutting accurately these adjustments sometimes don't work. and you have to resort to drastic measures like Mark did.
One way I've found to look at the wheel position and tracking is to use a bit of thin string (braided fishing line is ideal) instead of the blade.? Make a loop ~62" long (a bit smaller than the 641/2" std blade loop length so you can stretch it some when tensioning) and position it in the middle of the land?where the blade runs on the bandwheels.? Tension it up quite tight and see where it passes through the guides. It should be where the middle of the blade runs and not touching either side guide roller and should be clear of the back support roller by about 1/4".??
I bet you it's not!?
Taking off one or both side guide rollers will show where the blade wants?to run. That's how I found where to silver-solder the bits,?to position the guide rollers, when making a new set of guides
Like Mark found, if the rear support rollers are too far forward (esp the bottom one), the blade comes off, when you increase bow weight to make it cut quicker. This is because it's bending the blade across its 1/2" width and when the weight comes on, the blade pivots around the rear support roller and jumps off the bottom wheel (I use the saw with the head vertical and the viewer standing with the vice handwheel in front of them for any up-down/, back-forward bottom-top etc directions)? - jv?



On Thu, Feb 24, 2022 at 2:57 AM Mark <mark21056@...> wrote:
On Sun, Feb 20, 2022 at 02:05 PM, John Vreede wrote:
Then the bottom wheel is moved in or out on the drive shaft to get it to also track <0.040" from its rim.? You do this by changing the length of the spacer between the bottom wheel and the gearbox out bearing.
?

This is excellent information. I have a new saw (actually over a year old now) with some discrepancy between the ledge of the upper and lower wheels. if I remember right it's about .030" further out on the lower wheel and in my opinion it's not enough to worry about. I remember thinking the only way to fix this would be to move a wheel in or out but I wasn't really sure which wheel.?

I have something to add about blade tracking that is worth looking at. When I got my saw it seemed like everything was set up and ready to go so I started using it without making any adjustments. Then I started increasing the weight (it was cutting very slow) and as a result the blade started falling off. Most often this mutilated the blade and made it unusable. After the third blade I realized I needed to take a closer look. I found what I thought was the problem and then confirmed this with other saw manufactures.

First, (as you said John) the blade tracking need to be set with the blade guides removed. Then when the guides are installed they should twist the blade along the center line without deflecting downward or to the left or right. Ideally the bearings in the guide should only contact the back of the blade while cutting although it needs to just barely kiss the bearing all the time. Very slight pressure is also fine.?

The problem on my saw was that the blade guides were deflecting the blade downward nearly 3/8". With the guides set correctly the saw would not cut deep enough. The cover near the top wheel hit the base. Even when I removed blade cover the upper frame hit the switch housing before completing the cut. After doing a little research I realized my saw was defective. I looked at two other older saws that did not have this issue. I suspect this problem is a result of a bad setup at the factory. Maybe the pivot point for the head was not located correctly. In reality the pivot point on my saw needs to be dropped over 1/4".?

I ended up putting a 1/4" steel plate under my vise. This elevating plate raises the stock enough so that the blade can complete the cut without being deflected significantly by the blade guides. Since making this change I can increase the downward pressure to full. Sometimes the saw stalls but the blade never comes off. In fact, I have had the same blade on my saw almost a year now. It has cut a LOT of steel.?

I had a bunch of these elevating plates made (laser cut) and have sold over 60 of them (apparently quite a few saws have this defect). I currently have one plate in stock but if there's enough interest I can have some more made. When the price of steel went nuts I raised the price from $29.50 to $39.50 but honestly it's barely worth my effort. After the cost of steel, laser cutting and shipping I'm about $2 ahead. Let me know if your saw needs this plate. If there is enough interest I'll have more made.?

Mark
 

On Wed, Feb 23, 2022 at 05:26 PM, John Vreede wrote:
One way I've found to look at the wheel position and tracking is to use a bit of thin string (braided fishing line is ideal) instead of the blade.? Make a loop ~62" long (a bit smaller than the 641/2" std blade loop length so you can stretch it some when tensioning) and position it in the middle of the land?where the blade runs on the bandwheels.? Tension it up quite tight and see where it passes through the guides. It should be where the middle of the blade runs and not touching either side guide roller and should be clear of the back support roller by about 1/4".??
I bet you it's not!?

That would work well provided the string was positioned centered on the wheels Another problem with my saw was that the blade guides did not have enough adjustment. I milled one of the slots a bit wider to get it closer. I'm guessing my blade is still deflected down maybe and 1/16" but it's close enough that it doesn't cause any problems. If all these saws were made the same, a person could? design an after market blade guides but I'm guessing there is a lot of variations. With properly designed blade guides setup would be super easy! Picture this!?

1) Get the blade tracking correctly
2) install the guides with zero blade deflection and the top bearing just touching the back of the blade.
3) then rotate into position.?

It would easy to design but hard to make it fit all saws.?
 

I was able to get my new blade tracking correctly, by paying a lot more attention to the initial setup for the idler wheel tilt mechanism.? My experience with this has shown that the shaft can be moved in and out quite a bit while still being able to (kinda, sorta) adjust the tracking, at least on the undriven wheel.? If the fixing screw is backed out too much the blade will ride too far forward on the drive wheel, even though it's still possible to adjust the tilt so the blade is in the right place on the upper wheel.

What I did was screw the fixing screw in as far as it would go (after backing out the tilt-adjusting screw) and then in an incremental fashion work on getting the tracking correct.? This way the fixing screw is backed out just enough to get enough tilt:? and now the blade rides just fine on both wheels.? There also is much less variation in the tracking as I change the blade tension.

The bottom line is that there's a _lot_ of adjustment range in the tilt mechanism, perhaps to accommodate large manufacturing tolerances:? but as a result it's easy to get into trouble.

I also spent a lot of time adjusting the guides and now the saw is cutting pretty square.? Not perfect, but better than it was.? I used the ruler-clipped-to-the-blade approach:? and it IS important to go back and forth between the upper and lower guides.? If one guide is way off there's no way to get the blade nearest the other one to be perfectly vertical (at least in my experience).


Mark

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