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Author Topic: What we learned: waves and blade dives  (Read 1065 times)

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Offline Brad_bb

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What we learned: waves and blade dives
« on: April 15, 2017, 11:34:35 pm »
About three weeks ago, fellow FF member rjwoejk, aka Bob from Canada, was driving his semi over the road in the US and managed to time one of his required downtime stops at my place in Illinois.  He got here about noon and wanted to do some milling for a change of pace from all driving he'd been doing non stop for 3 months.  He has the same mill as me back in Canada- a Woodmizer LT15.  So we milled some cherry logs and the last log was a Honey Locust about 20 inches in dia. with some branch knots.  I was cutting as many 4x8 pieces of brace stock (timber frame knee braces) as I could get. 

 

 

I first slabbed 3 faces and on one of them I had a wave(dive) about 3/8 inches.  Bob asked me why that happened?  I didn't know.  I've been milling for a little over 2 years and have had my share of waves and dives.  Sometimes you get a wave, and sometimes you get a dive that won't come back up. He thought I should have a little more blade tension.  It was set where woodmizer recommends, but we increased the tension to where Bob says he has his mill set.   So then we continued milling and cut 4 inch thick slabs.  I set up 3 of the pieces to cut down to the 8" dimension.  I had the live edge plus another 2.5 inch to take off so I decided to make some 4" boards.  I started cutting and the blade dove.  Bob was really getting curious why this was happening.  He studied the outside piece and could see grain runout about 45 degrees toward the mill head(start of cut) where the wave started, see figure (1).  Bob suggested that when the blade hit the runout grain from the knot, it followed the grain and thus dove.  Since milling with the grain is much easier than cross cutting, it followed the path of least resistance.  It did cut across the grain, but was being pushed down by the harder grain lines.  It eventually cut through and came back up, leaving a significant wave.

 

 

Bob suggested an experiment - turn the can't around so that the runout grain would go up and away as you cut as seen in figure (2).  It worked!  So I wasn't sure why it worked at the time, but somewhere in my brain it kept rolling around.  Then recently it hit me- the guide rollers!  They keep the blade from moving upwards. So if the blade wanted to follow the grain in figure (2), it is more difficult because the guide rollers support the blade or resist against the blade in that case.  On the other hand, there is nothing to resist the blade form tipping down except blade tension.  Blade tension is not enough to resist the blade twisting downward away from the guide rollers.

 

 

In conclusion, I think grain runout in the direction of the opening end of the log and hardness of the wood can cause a wave or dive.  Having a sharp blade helps cut across grain with runout, but is not a solution by itself.  Adding tension above the factory recommended is of little help. I'll keep mine at the factory recommended tension.  Orienting the log so the runout points away from the front of the log helps the most. 

Many on here will indicate to orient a log with the small end at the front.  This makes sense for a fairly straight-grained log.  If the log has a lot of taper, orienting this way points the grain runout away from the front, consistent with what I've been saying.  But when you have a log with large branch knots, you may want to make the butt the front of the log(starting point) so the grain runout from the large branch knots points away.

This is my thinking from this experiment.  I will have to put this into practice more to gain more confidence in this.  It seems logical to me.... or maybe I'm sniffing the wood too much?  Weigh in.

 

 
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Offline Chuck White

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Re: What we learned: waves and blade dives
« Reply #1 on: April 16, 2017, 08:26:34 am »
Overall, it sounds like a good time was had by all, Brad! 8)

Seems that when 2 sawyers get together, at least one of them learns something new!   :P
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Offline Brad_bb

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Re: What we learned: waves and blade dives
« Reply #2 on: April 17, 2017, 07:53:35 am »
With all the questions that come up on waves while cutting, I'm surprised there hasn't been more commentary on this?
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Offline Rhodemont

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Re: What we learned: waves and blade dives
« Reply #3 on: April 17, 2017, 10:48:19 am »
I have been struggling with my red oak to overcome waves. Sharp blades,10 deg, 9 deg, 7 deg, faster, slower, frozen, not frozen, log orientation. Here is what I have found so far.  Playing with factory tension settings for blade and drive have made no difference.  Sharp 7 deg blades at moderate speed are doing well, want to try some 4 deg as I found improvement moving from 10 to 9 to 7 deg. My LT35 25hp will slow when it hits hard spots so I tried adjusting speed control as this occurred but have found it easiest for me to apply a little pressure by hand approaching and going through the knots to prevent taking off before I can turn down speed when the blade comes through the hard spot. Frozen logs did not wave as much as thawed do, I figure the freeze must outweigh natural changes in grain and hardness.  Partially frozen logs were a disaster, moving from freeze to thaw the blades went all over the place.  Overall the biggest impact I have found is orientation.  The butt of the bottom logs from the tree are hard, hard and I get dives just as I start into that end but do much better starting  from the top end so I hit the butt after already moving along. The second logs up the tree tend to saw about the same either direction as there are few if any knots.  The third logs start to have a lot of knots which lead to waves. Sawing these from the bottom end is working better because I get dives at the knots if come from the top.  Had one dive so hard it broke the blade. I agree that the guides provide resistance from rising as opposed to dives where the blade is getting stressed all the way out to the pulleys. Anything above that third log is firewood.

Offline Percy

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Re: What we learned: waves and blade dives
« Reply #4 on: April 18, 2017, 10:09:37 am »
Your theory of the "wave" in your case, seems more than plauseable. I tend to cut "butt first" most of the time as Ive had similar probs,results over the years.    Butt about a year ago(see what I did there :D), I was cutting 20 inch wide sitka spruce planks and I could not cut strait to save my life. Blade guides were accurate, blades sharp and set properly. Turns out, my band wheels were not on the same plane as eachother(idle side had tilted  and I was using the guides to correct the situation). I've yet to figure out why this affects my blade performance in such a drastic manner but as soon as I made the correct adjustments, the mill cut strait and true. So, in conclusion, I havent helped this disscussion at all, only made it more mysterious.... ;D ;D
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Offline fishfighter

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Re: What we learned: waves and blade dives
« Reply #5 on: April 18, 2017, 08:16:47 pm »
I had found that cutting from the butt end has help a lot. I saw a lot of different oaks. But, some times if there is a lot of stress in a log, I find it just so much better to just stop and put that sucker in the burn pile. :D I tried those and had just never won. >:(

Had a second cutting off a log the other day. Talk about a wild log. :o After the second cut, my blade dropped almost 1 1/2". :o But the butt log sawed out good. Just don't know what happen, but other then more firewood. :D

Offline Brad_bb

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Re: What we learned: waves and blade dives
« Reply #6 on: April 18, 2017, 08:23:16 pm »
As I said, my theory for orientation depends on the situation:
For a fairly straight log without big branch knots, Saw from the small end, but sawing from the butt end should work too.
For a tapered straight log without big branch knots, Saw from the small end.
For a log with big branch knots, or severe grain runout, saw from the butt end.

That's my theory that comes from this one log test.  I plan to practice more with it to gather more empirical evidence.
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Offline Ox

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Re: What we learned: waves and blade dives
« Reply #7 on: April 18, 2017, 09:05:26 pm »
It's very interesting and I look forward to following you in your findings.  Thanks for taking the time to share this with us.
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Offline moodnacreek

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Re: What we learned: waves and blade dives
« Reply #8 on: April 19, 2017, 01:04:20 pm »
Any saw wants to follow slope of grain. The smaller the blade and the farther apart the teeth the worse. On a circle mill, sawing small end first going down into a curved butt hemlock or spruce sometimes you have to inch or jog thru because the grain will bend that heavy saw spoiling the board and cant face.

Offline bandmiller2

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Re: What we learned: waves and blade dives
« Reply #9 on: April 19, 2017, 06:15:26 pm »
Seeing as we're brainstorming this wave/dive problem I have a theory I have yet to prove. One piece of advice often given is more set in A band that is waving or diving. I think less set may help as the narrower kerf will tend to support the body of the band and aid in a straight cut. I walk along with my band mill head and keep an eye on the flanged Cooks guides if they start to slow down its an indication the band is starting to dive. Most of the time I can slow the feed and keep it on the guide. It helps if you put a white mark on the back of the guide roller to view its rotation. Frank C.
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Offline JB Griffin

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Re: What we learned: waves and blade dives
« Reply #10 on: April 24, 2017, 12:34:57 am »
In my experience of sawing around 500mbf waves and diving are caused by dull, mis set blades or poor guide alignment,  or drive belt slippage. I can saw faster and flatter with the Baker at work than most can. Avg. around 5-6mbf daily in 8ft oak.
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Offline Crossroads

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Re: What we learned: waves and blade dives
« Reply #11 on: April 25, 2017, 03:01:34 am »
My waves and dives have gotten few and far between since I switched from 9-10* blades to 4*. Also, running the mill by the sound of the engine instead of a setting on the feed speed seems to have helped. I hit the wood at close to the speed I think I can cut, then adjust the speed to where there is a constant pull on the engine. The first time I hear the belts start to sing, I replace the blade because the next time it sings, it typically makes a wave or dive. I'm pretty new to running a mill, but this is what I've noticed in my learning curve.