bandmill blade questions

[chainsaw_louie]

Running the back of the blades to close to the guide roller flange is the biggest blade breaker when sawing hard,  You need 1/4"  between the blade and flange.  Soon as the blade hits the flange its going the crack the gullets  Steve

The WM manual is quite specific that the inner flange-to-blade gap should be 1/16" and the outer 1/8" .

Wouldn't a 1/4" gap allow the band to be pushed back onto the wheels and the teeth start to ride on the drive wheels ?

[Stephen1]

Running the back of the blades to close to the guide roller flange is the biggest blade breaker when sawing hard,  You need 1/4"  between the blade and flange.  Soon as the blade hits the flange its going the crack the gullets  Steve

The WM manual is quite specific that the inner flange-to-blade gap should be 1/16" and the outer 1/8" .

Wouldn't a 1/4" gap allow the band to be pushed back onto the wheels and the teeth start to ride on the drive wheels ?

No it would allow more room for the blade to run with out hitting the flange. 
Running a dull blade will result in pushing the head harder into the log, resulting in the blade running up against the flange. Thus resulting in a broken blade. 

[Magicman]

The blade guide flange is doing it't job when it stops rearward movement, but remember that the duller the blade, the more rearward movement you have.  Properly adjusted Horizontal Tilt pulls the blade into the blade guide when the blade contacts the flange.  This does put some stress on the blade but the rearward bending of the blade probably causes more.  If your bandwheel tracking is correct, even with 1/4" rearward movement, the blade teeth should not contact the bandwheel.

Dull blades are the principal cause of blade stress.

[ladylake]

Running the back of the blades to close to the guide roller flange is the biggest blade breaker when sawing hard,  You need 1/4"  between the blade and flange.  Soon as the blade hits the flange its going the crack the gullets  Steve

The WM manual is quite specific that the inner flange-to-blade gap should be 1/16" and the outer 1/8" .

Wouldn't a 1/4" gap allow the band to be pushed back onto the wheels and the teeth start to ride on the drive wheels ?

The 1/16 and 1/8 gap is way outdated.  Back when we ran 10 hp mills and higher hook angles the blade wouldn't push back much, now with higher hp mills and lower hook angles sawing way faster the blade pushes back a lot more.  Steve

[barbender]

I'd agree with Ladylake on this one, I put my top two out there kind of taking for granted that everything is properly setup. Touching those guide flanges breaks blades really quickly. I adjust mine just short of 1/4" back. 

When the blade is flexing back, it is spread out over a wide area of the blade. When they touch the roller flange, it concentrates the stress in that small area. I wouldn't think it was a big deal if I hadn't experienced it a few times. 

The things I watch to see how how dull a blade is, first the obvious if it isn't sawing straight. But then I watch how the sawdust stream is exiting, if it is spilling and making kind of a cloud instead of a nice compact stream, and then at the exit of the cut watch and see if your blade jumps ahead. Its a good visual of how far the blade is flexing back.

Yellowhammer made an excellent video on blade sharpness and things to watch for on his Hobby Hardwoods Alabama YouTube channel.

[chainsaw_louie]

Well, that's two voices of experience saying 1/4" gap works better than whats in the book, I'll check what mine is set at and make adjustments because I have broken a few blades lately.  Granted these are used blades but what you're saying makes sense.

Also, I did get the value of 1/16 & 1/8" from the current , online WMzr LT40 manual that covers the year my mill was made (2013).  They could easily update that value and should if 1/4" is better.  OTOH , they do sell blades 

I checked and the gap between the roller flanges and the back of my blade was 1/16" on both guides:


I increased them both to @3/16" . Probably they were set too close and caused my bands to break as per your suggestion.

[barbender]

I could live with 3/16 and 1/8".

[ladylake]

 No way I could run mine a1/8" back.  I'd be breaking a lot of blades.  I run 4 degree blades and push hard in tough wood, so a lot of push back.  Steve

[jpassardi]

I believe my manual says 1/8 and 3/16, I set it at whatever is recommended. Haven't had any issues but I only have 25 hp. I can hear it when the blade hits the back of the roller - the few times I have I know "the sawyer" pushed too long on a dull blade...  

[chainsaw_louie]

I'm not fully understanding what , if not the flange,  is resisting the backwards push of the blade while cutting.  The small settings in the manual seem to indicate that its expected that the blade will be pressing against the flanges.  Also, the standard advice given by WMzr and others about avoiding wavy lumber is to avoid cutting slow. Instead cut as fast as possible seems to be the rule of thumb. So, depending on how these factors interact:


- tooth sharpness.
- speed of band in rpm or feet per minute
- speed & forward pressure of blade teeth against wood
- rigidity of the blade ie thick and wide or thin and narrow

...it seems inevitable that as the speed of cutting is increased per recommendations ,  the  gap between the blade and roller flange is going to decrease and the there is going to be contact and bending pressure on the blade. 

Is the idea that the crown of the wheels is enough to resist the rearward pressure on the blade and the blade shouldn't touch the flanges or just very lightly?

To my thinking, instead of the blade-to-flange gap setting,  the the 4 factors above (band sharpness, band rpm, fwd speed, band rigidity) will determine how much pressure gets put on the flanges resulting in blade stress. But that's just me thinking , you guys have the experience factor and know what actually works.

Thanks.

[doc henderson]

I think the band wheel alignment help keep the blade tracking in the center, and the guide wheels make the blade flat and have more tension in the cut area.  Ideally there is a little room to flex but too much and the blade will start to drift in the cut.  the flange is a safeguard but not meant to be used.  If it is flexing that much, you are about to break or dismount a blade.  I think @Magicman talked about the tracking of the guide wheels being at a certain slight angle to keep the blade off the flange.  My band and guides are all adjusted flat across the face and do fine.

[Magicman]

Your questions are valid but a single cut & dried answer that everyone would agree on is elusive.  While I may disagree with some of the statements/replies on this topic, I understand them and also the reason for those statements.  Our individual preferences are based upon our experience with what we have, what we saw, and with what.  Log species, blade profiles, and probably above all, blade sharpness will determine the blade push back.  

When a flat blade pushes back, (bows) it has to either stretch or wrinkle.  If it wrinkles, it will cause dips and waves in the lumber.  Hopefully the blade guide flanges will stop the rearward blade movement and keep it flat and from wrinkling.  Proper horizontal blade guide tilt will determine how well the blade guide handles the blade without any vibration.

Remember that the width of the cut enters heavily into this blade push back situation, but there is no substitute for a sharp blade......no....no....none.   

[TreefarmerNN]

My admittedly inexpert knowledge says a properly sharpened and set blade will pull itself into the wood rather than being pushed by the rollers.  It's the operators job to keep the carriage speed matched to the blade travel into the wood speed.  Too slow and the blade recuts the kerf and starts to wander due to sawmill building up in the cut.  Too fast and the blade doesn't pull itself into the cut as fast as the carriage is pushing.  Just right and you hear it sing.

I'm guilty of both too slow and too fast at times and pay the price in a thick and thin board.  I'm also guilty of running a dulling blade because it's the last log and only a couple more cuts. . . In fact, I'm guilty of a lot of sins with the mill- too many to list, lol.

[Ben Cut-wright]

- tooth sharpness.
- speed of band in rpm or feet per minute
- speed & forward pressure of blade teeth against wood
- rigidity of the blade ie thick and wide or thin and narrow

...it seems inevitable that as the speed of cutting is increased per recommendations ,  the  gap between the blade and roller flange is going to decrease and the there is going to be contact and bending pressure on the blade. 

Is the idea that the crown of the wheels is enough to resist the rearward pressure on the blade and the blade shouldn't touch the flanges or just very lightly?

To my thinking, instead of the blade-to-flange gap setting,  the the 4 factors above (band sharpness, band rpm, fwd speed, band rigidity) will determine how much pressure gets put on the flanges resulting in blade stress. But that's just me thinking , you guys have the experience factor and know what actually works.

Thanks.

The four factors you list, and others, are influencing how much push back the blade sees.  The flanges are fail-safes to limit max push back, not meant to be continually forced to control a dull blade or too rapid forward travel.  The bending stress is concentrated between the guide rollers when the blade is running hard against the flanges. ALL push back factors must be accounted for when sawing in order to prevent extreme/constant flange-blade contact pressure.

Blade contact is only "inevitable" when factor/factors combine to make it so.

The "crown of the wheel" is a component of blade tracking.  Strain on the blade and resultant friction with the wheel surface is why the blade attempts/continues to track properly when push back occurs. 

It's not so much a matter of "instead of blade-to-flange gap setting " as it is the gap is another factor to be acknowledged.  IMO, WM recommendations for flange gap are made considering precisely correct operation using a perfectly sharp blade.

[KenMac]

I think two other factors enter in to blade deflection- Band cross section and tension. I've watched YouTube videos that show the blade to flange setting while cutting and the band deflected almost to the flange. I'm thinking it was 1 1/4" x.045. I have since watched mine in a cut and see no deflection at all. I run 1 1/2x.055 bands at the tension recommended by Cook's.

[Magicman]

No question about that.  Wider and thicker would deflect rearward less, if for no other reason, it is stronger.  

I could never opt for .055 thickness because of the 19" bandwheels, but I could have switched over to 1 1/2" wide.  I should have done that when I dropped my blade inventory and switched from 10° blades to T7° but I did not and now I never will.


I wonder how much rearward movement the blade on this sawmill has?


I don't know how thick it is but it is 8" wide.

[customsawyer]

Now think of a double cut mill. One that cuts in both directions. Granted they are a wider blade, normally at least 3", but they couldn't even touch a flange or it would ruin the teeth. You don't want our blades to be hitting the flange either. All it does is cause bad stuff to happen. The blade tension, and the 1/4" down pressure, should keep your blade running where it's supposed to.  

[Stephen1]

Remember that the width of the cut enters heavily into this blade push back situation, but there is no substitute for a sharp blade......no....no....none

This is the absolute. You can not do any of the others without this. 

[barbender]

Excellent point, Jake.