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What causes this?

Started by Bucksaw, October 24, 2016, 11:38:20 AM

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Bucksaw

Brand new blade. It isn't happening consistently, so I am unsure of what is causing it. Accuracy of cut is perfect.



  

thecfarm

One tooth or more has more set than the others.
Model 6020-20hp Manual Thomas bandsaw,TC40A 4wd 40 hp New Holland tractor, 450 Norse Winch, Heatmor 400 OWB,YCC 1978-79

terrifictimbersllc

Looks like blade vibration/flutter to me.  After checking the damping device (a screw on about 1/8" above the top of the blade for Wood-Mizer), blade tension, I'd experiment with different constant cutting speeds and also how fast you enter the log. 
DJ Hoover, Terrific Timbers LLC,  Mystic CT Woodmizer Million Board Foot Club member. 2019 LT70 Super Wide 55 Yanmar,  LogRite fetching arch, WM BMS250 sharpener/BMT250 setter.  2001 F350 7.3L PSD 6 spd manual ZF 4x4 Crew Cab Long Bed

Weekend_Sawyer

looks like your feed rate is varying quite a bit.
Is this an auto feed saw? I had the feed rate potentiometer go bad on an LT35 making it surge and dive.
Imagine, Me a Tree Farmer.
Jon, Appalachian American Wannabe.

kelLOGg

Glad you asked but I can't help. I have seen the identical thing. Even entering the log at cutting speed the pattern comes and goes.. but not always. I saw it sawing CoffeeTree Saturday. It probably is tension related but it is not consistent.
Bob
Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

Bucksaw

The mill is manual feed, so I may be in fact being inconsistent in feed rate. Blade tension is hydraulic and I try to keep it in the Mfg suggested range of between 1200 and 1300 psi. Tooth set maybe also, even with a new blade.
I will have to keep trying different things I guess.

Chuck White

I have noticed this over the past few years of sawing and have come to the conclusion that it is caused by the blade not entering the side of the log at 90°, hence, usually smaller logs.

Usually happens (for me) on W/Pine when I'm sawing some of the upper logs where the bark is smooth.

I've found that if I pick up feed-speed, the result usually decreases.

When that happens, usually the next cut down is good and no ripples in the cut.
~Chuck~  Cooks Cat Claw sharpener and single tooth setter.  2018 Chevy Silverado and 2021 Subaru Ascent.
With basic mechanical skills and the ability to read you can maintain a Woodmizer  LT40!

pineywoods

Loose, slipping drive belt. The blade slows down and vibrates.  It may actually be worse with a sharp blade. Not enough band tension can do the same thing, the drive wheel spins on the blade.
1995 Wood Mizer LT 40, Liquid cooled kawasaki,homebuilt hydraulics. Homebuilt solar dry kiln.  Woodmaster 718 planner, Kubota M4700 with homemade forks and winch, stihl  028, 029, Ms390
100k bd ft club.Charter member of The Grumpy old Men

Bandmill Bandit

Quote from: pineywoods on October 24, 2016, 08:55:06 PM
Loose, slipping drive belt. The blade slows down and vibrates.  It may actually be worse with a sharp blade. Not enough band tension can do the same thing, the drive wheel spins on the blade.

What he said times a few 99% of the time. The other 1% is worn out wheel belts where the band is riding the steel of the v-grove wheels.
Skilled Master Sawyer. "Skilled labour don't come cheap. Cheap labour dont come skilled!
2018 F150 FX4, Husqvarna 340, 2 Logright 36 inch cant hooks and a bunch of stuff I built myself

bandmiller2

I believe its a combination of factors, a resonance, likely started by one or more overset teeth that tends to propagate. Frank C.
A man armed with common sense is packing a big piece

Ox

The different angles of the waves in the wood gives the only clue I need.  This is caused by harmonic vibrations from the engine and rotating masses of the bandwheels and blades.  All the vibrations build up and down getting worse and better in waves.  Weird stuff but very real.  Whenever I got this in my lumber, I would have to play with the tension.  I also got it if I tried to feed too fast.  I also have a hydraulic tensioner, but mine always rides above 1500 psi.  In fact, I've been running at around 2500 psi lately with good results.  Next time you get these types of cuts, look at the back of your blade at the top or bottom while it's running full throttle, not in the cut.  I guarantee one or the other, or both, are fluttering so it looks like the blade is "out of focus".  It'll look blurry.  It might come and go taking a minute or two to happen, but it'll happen.  You need to adjust the tension on the blade so it's gone.  Follow this: http://www.suffolkmachinery.com/six-rules-of-sawing.html
It'll get you on the right track.  Now, following the directions at suffolk, I find there's at least two tensions that will flutter and then go away.  Once at around 2000, then another at 2500.  Each blade is slightly different.  It's up to you to fine tune the tension to get the flutter away.
Good luck and please let us know what you tried and what worked so others may learn from your thread.  :)
K.I.S.S. - Keep It Simple Stupid
Use it up, wear it out, make it do or do without
1989 GMC 3500 4x4 diesel dump and plow truck, 1964 Oliver 1600 Industrial with Parsons loader and backhoe, 1986 Zetor 5211, Cat's Claw sharpener, single tooth setter, homemade Linn Lumber 1900 style mill, old tools

Bucksaw

Interesting stuff! I have some cedar ready to saw and will see what happens. I will check the drive belt also.
Thanks for all the help.

YellowHammer

Resonance is very easy to check, and is something I check as soon as I put a band on the saw and adjust tension.  No need to saw into a log to determine if you have it.  Look at the band while it is running and increase and decrease the tension adjustment.  You will clearly see the band vibrating and fluttering and then getting rock steady and laser beam flat and quiet.  So if you have a fluttering band, and go into soft wood with a sharp bands, the band will dig in leave the marks. 
YellowHammerisms:

Take steps to save steps.

If it won't roll, its not a log; it's still a tree.  Sawmills cut logs, not trees.

Kiln drying wood: When the cookies are burned, they're burned, and you can't fix them.

Sawing is fun for the first couple million boards.

Be smarter than the sawdust

Cutting Edge

Quote from: YellowHammer on October 25, 2016, 11:02:44 PM
Resonance is very easy to check...  No need to saw into a log to determine if you have it.  Look at the band while it is running...

There is alot of truth in what YellowHammer has stated.  In my experience, Band Wheel Belts can be/are a HUGE contributing factor to vibration/resonance issues.  This can be the belts themselves, due to construction and/or composition of materials, amount of wear of the belt(s) and buildup of sawdust under the belt and/or wheel.

I am willing to bet you are utilizing a blade with to aggressive of a hook angle in combination with to small of an engine:  10 deg. hook angle blade with a 13 hp engine which has a very narrow (rpm), hard to sustain/maintain torque curve.  Combine this with the wider cuts as you have posted in your pictures and I have no doubt the root cause is directly related to one or more contributing factors mentioned.

Try switching to a 4 deg. hook angle blade and your sawing should improve on many levels.  Even your feed rate will probably increase because the lower hook angle will allow the 13hp engine to work more efficiently. The load will be much more consistent and in turn, easier for you to control.

Now, as for the "flutter" test that was mentioned...  That is what Suffolk suggest for THEIR blades, that doesn't mean it is right for ALL blades out on the market.  To be honest, I feel it adds another element of confusion... especially for someone who is just beginning to learn. 

Most carbon steel blades on the market are manufactured and capable of being tensioned in excess of what the mill itself is designed to produce without damaging components.  That is major contributing factor that allows both hobby and production sawyers to produce a satisfactory product. 

BuckSaw, tension your blade to what SMG suggests, check a few things and try a less aggressive blade.  The improvement(s) should be immediate.

Hope this helps you out.
"Winning an argument isn't everything, as long as you are heard and understood" - W.S.


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Bucksaw

The cedar in the pic was cut with a 7 degree blade that I had used on one Basswood log prior. The same thing happened with the Basswood log. I will have to try a 4 degree blade and see how that works out.
I'll post an update after I play with it a bit.

Thanks again

Davek603

My log LT40 was doing that and breaking blades. Turned out the drive belt was slipping under load even though you couldn't hear it. Changed the belt and my problems went away.
Woodmizer LT50 and lots of iron to go with it

5quarter

One other thing to check, in addition to cutting edges remarks: inside surface of the blade body. unless you're using a felt wiping system to keep your blade clean, you will occasionally get resins  sticking to the blade body. they will pick up sawdust and get compacted by the blade guides as they spin and will ultimately set up a flutter between your guides. the resin is not obvious as it is often black if you're running a water or diesel drip. I have had flutter on boards like you show in your picture and each time it was resin spotting on the blade body that caused it. Also, if your blade has some discolored areas from surface rust, those ares will pick up the resin first.
What is this leisure time of which you speak?
Blue Harbor Refinishing

Bucksaw

How much build up is enough to cause flutter? I was able to scrape some off the inside of the blade as well as some on the wheel belts.

esteadle

When I get sawdust compacted on my blades, it's because I'm not dripping enough lube.

I mostly cut hardwoods like Ash, Cherry, Oak, Maple (soft and hard) and Walnut, and even a slow drip is enough to keep the sawdust from building up on the blade.

But Pine sap is sticky, and it likes to adhere to the blade. Even a really fast drip doesn't always to clear it. I can sometimes get by with increasing the lube drip rate. But to really prevent pine pitch from building up, people say mix Pinesol into the lube. I've done this and it works.

In fact, I had a customer this summer who had 40-50 white pine logs cut just after spring, so the sap was really running in those at the time, and the logs were full of pitch -- oozing out of ends, and flowing out when I cut into a pocket. It was causing the sawdust to build up and not just "flutter" the blade, but drive it down and cause the blade to wander off into the next board! So I mixed in about a cup of the Pinesol per gallon of water, and let it "flow" rather than drip. That did the trick and we had no further trouble.

When I'm cutting, if the dust does accumulate on the blade, I'll take a scrap piece of wood with a square edge, and scrape the inside of the band as it's slowing down (after I release the clutch). This lets the lube drip "catch up" and clears the rest of the blade (usually). That can be kind of dangerous if you don't know what you are doing. Fair warning. ;-)


Bucksaw

I cut a fresh Eastern White Cedar log with a new 10 degree Lenox Woodmaster C blade and had no blade flutter/vibration issue at all. Every board was perfect.
The only thing I did differently was to clean some sawdust/pitch build up from the belts and guides. I also mixed my washer fluid blade lube with more dish soap and Pinesol and flooded the blade after the cut until I could see the pitch residue was off the blade.
Could it be that just some pitch/sawdust residue on the belts and guides is enough to cause a flutter vibration? Time will tell. Stay tuned...

Ox

Yes.  Pitch buildup will cause flutter.  Smooth is a clean cut and clean parts is a smooth cut.
K.I.S.S. - Keep It Simple Stupid
Use it up, wear it out, make it do or do without
1989 GMC 3500 4x4 diesel dump and plow truck, 1964 Oliver 1600 Industrial with Parsons loader and backhoe, 1986 Zetor 5211, Cat's Claw sharpener, single tooth setter, homemade Linn Lumber 1900 style mill, old tools

GDinMaine

I get the same thing when the feed rate is too slow. When the blade enters the log as I turn up the feed the first 4-6" of the cut looks like that. Try to increase your feed rate a little and be consistent with it.  See if that helps.
It's the going that counts not the distance!

WM LT-40HD-D42

Brucer

Definitely blade resonance. The blade has a natural frequency and something is forcing to vibrate at close to that same frequency.

Things that can affect the natural frequency (same as a guitar string.) ...
- Thickness of the blade (diameter of the string). Thicker = lower frequency.
- Buildup on the blade (same as a wire-wound string). Buildup = lower frequency.
- Width of the blade (diameter of the string). Wider = lower frequency.
- Length of the unsupported blade (length of the string between the fret and the bridge). Longer = lower frequency.
- Tension on the blade (tension on the string). Lower tension = lower frequency.

Things that can affect the forcing frequency ...
- tooth spacing. Closer spacing = higher frequency.
- blade speed (a slipping drive belt will affect this). Tight belt = higher frequency.
- blade guide roller diameter. Smaller diameter = higher frequency.


Things that can amplify the forcing frequency ...
- tooth angle.
- blade sharpness.
- blade misalignment.
- carriage travel is too high.

Even when there is a resonance situation, it is often damped out so you don't really notice it.
- Green wood usually damps out vibration.
- Dry wood doesn't.
- Lube on the blade will sometimes damp out vibration.
- Width of cut.

Some of this stuff you have control over, some you don't. It doesn't matter which way the two types of vibration change, as long as they move further away from each other. Vary one thing at a time, and make sure your changes don't counteract each other.

And sometimes you can't fix it no matter what you do ::).





Bruce    LT40HDG28 bandsaw
"Complex problems have simple, easy to understand wrong answers."

Bucksaw

I experienced the flutter pattern on green logs as well but it seemed to be more pronounced with a dry cedar. I will be keeping an eye on it and tweaking things if required.

Thanks for the help and excellent info.

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