How flat does your bandmill cut through knots?

[Kelvin]

I've got a realively new LT-40 woodmizer, and was having some difficulty cutting wider boards without really bad waves.  I'm talking in the 1/4" deflection area.  So, i started tuning up the guides to make sure they were factory spec.  I found the factory doesn't really set up the mill very well, or the mill doesn't hold the set-up very well, but it was all very badly done.  So, in trying to correct what i had going on i started noticing that none of the boards i've sawn are "flat" flat.  Every knot in hardwood (white & red oak) causes a deflection, but not too bad.  IS this too be expected?  When i put my straight edge on the board, the deflection is in the .025" to 1/128", and gets worse as the blade dulls, maybe after 200 bd ft of clean green wood.  Is this acceptable?  What else would you say would interact with the wave?  I have double hard blades from WM, set for hardwoods.  Maybe i need to check the wheels themselves, but its hard to tell if its the chicken or the egg thing.  What is the most common cause of this deflection?
One thing i notice, that i hadn't noticed on other peoples mills, is that the blade really "Flaps" in the guides while its running outside of the wood.  really vibrates hard.  The ceramic guides are set perfectly to .010" just like the guy at WM suggested.  Any ideas?  THanks
KElvin

[Tom]

Waves over knots are caused by the change in grain direction and cross grain of the knot itself.  Usually it is a dull blade that causes the problem.  A blade with not enough tension can cause it too.

If the tension is correct on the blade then something may be out of balance.   Look under the V-belts for a wad of sawdust or chip of wood.  The belt may be faulty as well but not probably.

Some woods are prone to causing this kind of problem more than others. Loblolly pine, here, is very prone to causing the blade to follow the grain.  The only answer in that case is a very sharp blade and change them often.  That doesnt mean that the blade is no good, just not good for anymore of that wood.  It may still be sharp enough to cut other stuff.

The "off-set" of the rollers can be a factor too.  You need the down pressure to guide the blade. You also need the guide cocked out just a little bit on the "exit" side of the blade so that the rotary motion pulls the blade up against the roller.   The lip on that side should touch the blade first.

Don't go overboard with any adjustment and only change one thing at a time or you will never find the problem.

[beenthere]

Tom (and others)
Have you noticed any difference in blade wave sawing through knots from the 'top down' vs the 'bottom up' ?  Given that the steep grain around a knot is affecting the cut line, approaching the knot from one direction vs the other may help in keeping a straighter kerf line, for a longer time.
I realize there is a sawyers' preference (butt first or top first), and just wonder if direction, when sawing through knots (they are also different by species, and the grain deviation around a limb (knot) is different under the limb vs. above the limb), is important when deciding how a log is loaded on the mill.
My guess is sawing through knots from the top down would be better, but don't actually know.  ???

[MrMoo]

Kelvin,
Ya I run into this when sawing spruce. It takes a really sharp blade to get it straight and even then its difficult. So far only the Monkey blades seem to give me what I want and they only go a few hundred board feet. My best results with spruce is when its frozen.
What Tom mentions about the blade not being good for Loblolly is also true for spruce. I have taken blades that I couldn't use in spruce anymore & cut oak with no problem.
Beenthere your comments are something I have thought about too only because when I split firewood I found it splits easier going up the tree than down. Not sure if it applies to milling thought.
I'll be interested to hear what have to say about this stuff.
Mike

[Tom]

I saw "top down" preferably.  Sawing through knots does seem to be easier.  I find it easier to read a log and place the blade and level the log and all kinds of stuff.  It seems that the blade handles "rising" grain better than "falling" grain too.

Some like to saw butt first because the slab is easier to reach on a Horizontal band mill.  It gets rid of the widest part of the log first when cutting oversize logs too.  That means that the Whittlin' gets done before the blade enters the log rather than "as you come to it".

I'll saw "top down" every time, given the chance.

Here is a thought, if you don't hold me to finite accuracy.
A log is only as big as it's small end.
You judge a timber based on the small end of the log.
It's easier to have the small end right in front of you where  you can see the blade enter than at the other end of the mill where you have to guess where the blade will come out.

[beenthere]

MrMoo
Splitting firewood is where I picked up on this thought too. If I am hand splitting, I split bottom up because it is easier, but the split follows out on the grain at the knot.

 If I am machine splitting, I split top down because I think the split is straighter through the knot (have to have just straight pieces to stack well  ;D )

[Norwiscutter]

I have had some difficulty with getting perfectly strait boards out of Red Pine. The Dang knots are very hard compared to the rest of the wood, and seam to cause a little blade deflection no matter how sharp the blade is or any other variable.  That being said, one can minimize the deflection by consistantly addressing the common items associated with blade deflection.  A sharp blade always seams to remedy most of the problems that I have with deflection, or at least to the point that I can live with it. If I have 1/16 deflection, I'll live with it. Some times even an 1/8 depending on what I'm cutting.  I can't seam to ever get anything consistant with cedar for instance, because of all the tension in the wood. But if it is something that will work its way out when I run it through the jointer, planer, etc., I don't worry to much.  It ain't worth it to me to change the blade after 4-5 hundred feet to remedy a problem that I can solve in a different capacity.

[Rod]

 I smash the rollers on the guides tight on the blade were it has no play and that way the blade has no were to go but strait.

And I tighten the blade if I start getting waves.

But I don't know about woodmizers tho so my way may not apply.

[raycon]

No answer here but I experience the same tracking problem in red pine and spruce as well. I use the 10degree double hards for everything at this time. I also find I can take the same band thats tracking with the knots in spruce and cut another 300 bdft of hickory with minimal issues.
If I pay attention  in spruce and slow down the feed before sawing through a large knot I can minimze the tracking.

After re-reading the post. I have more problems in the softwoods(spruce/red pine) than hardwoods.

[Neil_B]

Kelvin,
If you are getting any vibration in the blade it is going to cause you problems.
Couple things to look for is proper tension, proper down pressure on guides or something out of round such as the wheels or guide rollers. Even something stuck to the blade or it could have a bend in it somewhere.
I'd try to find the cause of the vibration first.

[rbarshaw]

The "off-set" of the rollers can be a factor too.  You need the down pressure to guide the blade. You also need the guide cocked out just a little bit on the "exit" side of the blade so that the rotary motion pulls the blade up against the roller.   The lip on that side should touch the blade first.

Hey Tom could you explaine 'cocked on the exit side' a little more please. I use Cooks roller guides.

I've cut nothing but SYP and a couple sticks of sweetgum, I've always found that cutting top down is best. I've even made the mistake of putting the log on but first, discovered it the first cut, then take it off and turn it small end first, and it cuts straighter.

[Tom]

I don't know what Cook recommends but the Wood Mizer manual (same type guide) Says to line the guides up so that the blade is horizontal to and in the same plane as the bed, and the amount of down pressure has been set.

The final adjustment is to cock the guide laterally just a wee bit so that the shoulder on the output side of the wheel contacts the blade before the input side does.  You do this to both guides.  The theory is that the shoulder on the back of the guide wheel will be pulling the blade up tight against the surface of the wheel.  

If the shoulder on the input side of the wheel hits first, the blade will be pushed away from the surface of the wheel.

To picture this, assume this image.

Stand in front of the blade with the teeth pointing toward you.
Their direction of travel, when cutting, will be to the right.
The guide wheel's direction of travel will be counter-clockwise.

Cock each guide assembly to the left.(that makes the shoulder on the right side of each wheel contact the blade first and the shoulder on the left side of each wheel lag behind just a little bit.

The shoulder on the left side of each wheel is going down ('cause the wheel is going counter-clockwise).  If it contacts the blade first then it will be trying to climb over the blade.

I wish I had my Wood Mizer manual here.  They probably explain it a lot simpler than this.  If you are lost, let me know and I'll try to draw a picture.

[rbarshaw]

Thanks Tom, I get it now. I guess I must have built mine backwards tho',  ;D the blade goes to the left while facing the teeth ( I'm not weird en ough to get in front of it spinning tho'). I"ve been wondering why i had to turn the blades insideout to get the teeth to point in the right direction to cut. ;) ;)

[RMay]

I would look at more set in the blade & slow down at the knots it works some times ;D

[beenthere]

Tom
When I went to the WM site and to their guides, seems I was able to better pick up on what you were explaining about 'cocking' the guide.
The site shows the guides (these the shouldered ones you were referring to?) at the beginning of the message.
http://www.woodmizer.com/support/techtalk/rollerblockguide.html

[Tom]

rbarshaw,

that may end up causing you more problems.  It was explained to me that a blade has a natural curve that is developed when the band is made.  A blade can be made backwards such that  the curve in the blade fights the guides and the crown on the wheel.   In 1992 or 93, Woodmizer put out a lot of blades one month where the bulk reel had been put on the machine backwards.  None of us could get the things to work and Wood Mizer replaced every one.   I was told that it would take about 3 sharpenings for the blade to get to where it might ride properly.

Now, I'm saying this like it was explained to me without knowing all the engineering envolved.  If you are really interested in it, you should ask the blade people for an explanation.  

You may be able to specify the direction of travel of your mill and get a blade that will work better.

beenthere
The new guides they show are different than the ones I used only in that they aren't rebuildable and have pressed bearings.  I would assume that the line up is the same but manuals should be checked.

[chisel]

You may be able to specify the direction of travel of your mill and get a blade that will work better.

I don't have a mill and have never run one ( planning to build one, so I've read all I can), but according to this article by Tim Cook, having a blade made and "conditioned" for the saw's direction will indeed work better. I have no affiliation with Cook's, etc., etc.

http://www.cookssaw.com/Articles/bandsawblades.php

[Norm]

The problems I have with blade diving is in white oak knots (don't get any softwoods here), I've tried most things described and the only things that have helped are keeping the tension tight, freshly sharpened blade, soapy water, and going slow through them. That being said I still get blade wander through those areas, a 1 1/4" blade is not stiff enough no matter what you try or how good the guides are.

[gmmills]

Kelvin,
    If you are only using  1/8" downward guide deflection as my manual states for roller block guides change the deflection to 1/4". With an 1/8" deflection the rollers may stop turning and develope flat spots. These flat spots will cause the blade to vibrate badly. When I picked my mill up. It was set  up this way and the outer guide roller flat spotted in only 11HRS.
    Your blade body may be bent or twisted also causing the vibrating.
    If you are using 10 deg blades ,they may be too agressive for the hard knots . This can cause the blade to deflect up or down over the knots.For hardwoods I use hook angles of 8 or 9 deg depending upon how hard the wood is.

[ARKANSAWYER]

  The thing that gets my attention is the blade flutter.  It should not be doing that.  Your outside moveable guide should only be about 1 to 1.5 inches from the log.  Your pressure gauge should be reading about 2100 psi (orange area).  Your blade out side of the log should be running smooth.  If you have flutter then I would check the B-57 belts and the grooves in which they run.  Check the tension of the drive belt.  If it is loose it will cause a vibration which must go some where.
  I adjusted my machine when it was new about once a month for 3 months.  Last time I checked it was last year some time and I have over 1 million bdft on it.  I guess it is seated now.
  I saw with a 10 degree, 0.045, 1 1/4" WM blade and saw most every thing with it.  I have some 10 degree 0.055 1 1/4 WM blades that will let you cut faster in hard and knotty woods like hickory.  I had a few 13 degree 0.055's and I could really fly in SYP knots and all.  Does it cut like this with a new blade?
   Check and adjust one thing and try it so you can see if there is any change.
  Also one must remember that this is sawmill lumber and is not machined.  I would be concerned over 1/4 inch dip in a board but most plainers can take out 1/128th.  A knot will dry with more deflection then that.  Some times a feed rate that is to slow is as bad as one that is to fast.  If the saw dust is hard packed on the boards the the set is to small or dull.  To much lube is as bad as none.  Cutting from the little end does help.  And by the way just how big are these knots?  They just drop the grade any way.   I can shave boards that are 0.030 thick and not have holes in them.
ARKANSAWYER

[Bibbyman]

Kelven,  

Has this wavy cuts, dip in the knots,  and blade flutter problem just started or has it been there from the beginning in some degree?  What year of mill do you have?  How many hours are on it?  Do you grease the guide rollers often?

If it's been a problem from the start,  and you've tried most everything to adjust it out,  could be you have a roller guide or both that is defective.  

When you have the blade off do they turn smoothly with no play or wobble?  If they don't,  that could mean the bearing is out.  

If they turn smoothly and there is no wobble,  check to see if the roller is round.  I'm not just sure how unless you have a machinists dial indicator.  Maybe a feeler gage between the roller and the guide and then slowly rotate the roller guide to see if it maintains a constant gap or if it's loose in some spots and tight in others.

You may be able to detect if the rollers are out of round by watching them turn as the blade is running or sawing or when the engine has been disengaged and the blade is coming to a stop (while it is turning slow).

Otherwise,  our experience has been pretty much the same as Arky's.  I set the guide clearance to the inserts when we first got the mill and have not touched them since.  

[EZ]

When I get a wave in a board I know what is causing it right away. My one guide has moved away from the blade a little. Why it does this every so often I havent a glue, but I just adjust it up and the waves are gone. I keep 1/16 inch from blade to back, works fine for me.
EZ

[Kelvin]

THanks for all the replies guys.  So, does everyone think i have too much deflection, or its to be expected?  I know boards aren't perfect.  Maybe this is all i can expect?
I have adjusted everything to factory specs on the guide rollers.  Down pressure, camber, cant and the distance to the flange.  Bearings feel fine with no wobble.  One thing that Arky mentioned was too much coolant.  I use a lot all the time, b'/c i can't imagine that i'm getting enough in there for a 20" wide cut.  Is this a possiblity?  The mill cuts worse now than new.  It has 150 hrs on it.  The blade only flutters when its running outside of the wood.  Maybe i should try change the bandwheel tires?  Guides might have developed a "flat" if its as easy as some of the messages have mentioned.  I can check this as well with my feeler gauge and the ceramic disks.  Is 1/64-1/128 exceptable to you guys for knot deflection?  I don''t saw softwoods so i don't know how they would handle.  I use 9 degree hook blades for hardwood by WM.  THanks
KElvin

[Fla._Deadheader]

  For what it's worth, we saw a lot of SYP and when you come to a knot, you better have a sharp blade, or the blade will try to ride up and over the knot.

  We do not use the high tension that WM owners use, and we have a LOT more blade to keep steady than WM owners, but, the little bit of flutter we get, at times, will immediately stop as soon as we cut into the log. We use 10-12° hook on everything. We have a bunch of HARD Live Oak to saw next week. It is actually easier to saw hardwood logs than to saw SYP. It doesn't seem to matter much going from the normal hard wood to a knot.  I would not worry about the little deflection around a knot. That's what Planers are for.  ;) ;) ;D

[FeltzE]

Spending most of my sawmill time in knotty SYP, loblolly, and knotty white pine I can understand your problems.

The first thing I would do is to make a quick check of the mill which you have already done. Making sure that everything is in line with the manual.

Second, I would grab a fresh knott free (truely saw grade) log and start sawing. This will establish a base line for whether the saw is in fact sawing right. If you can saw a straight line with appropriate feed rates then you can pretty much confirm that the mill is set up properly. A cut that pulls up and stays there or down for that matter is probably a mill adjustment, a wavy cut always seeking back to center is too fast a feed rate or a blade set or sharpening problem.

Then I'd go back to a fresh green knotty piece and try that slowing PRIOR to the knots to allow for the saw to keep uniform pressure on the teeth. Excessive feed pressure in the harder wood around the knot can easily cause the blade to deflect. Especially if you are cutting big stock, the demonstrations I have seen often have moderate saw grade timber 12-20" diameters, those will square out to under 14" and you don't have a lot of blade in the cut with your guides fairly close together providing a lot of support to the blade. If you are in a cut at 14+ inches wide your guides being farther apart can't provide as much support to stabalize the cut. So slower feed rates apply again. It becomes a beam factor of blade strenght, the larger the blades beam the stronger it is.... etc etc... greater feed rates ,.. straighter cuts, more hp req...

Try increaseing your set a couple thousanths too.

The dryer the wood the harder to saw, compile that with knotty soft woods and you have a real challange to sawmill!

If you are getting a lot of vibration in the head when you spin up to speed (if the drive belt is tight enough) try a B56 v belt instead of the WM recommended B57, its a real bear to get on and I always cut them off the wheel when done but you will not have to mess with wheel belts but once ever couple hundred hours with no slap!

My 8 cents worth

Eric