rough surface with 747 blade

[postville]

I tried some 747 blades and got rough surfaces. LT40, 28 HP motor. I tried to vary the feed and checked the belt tension. Looks like blade was vibrating.
Material cut- poplar and basswood, 14 inch diameter.
I put on a Double Hard 10 degree,  1 1/4", 7/8 pitch, .042 blade and everything settled down.
It was suggested I don't have enough power, that the 747 blade is very aggressive.
Your thoughts?
Bob

[barbender]

Aggressive blade profiles like the 747 and 739 require a fast feed speed, or they make ripples.

[Magicman]

Looks like you do not have the HP/speed to empty those deep sawdust filled gullets.  

[postville]

Would sharpening to 10 degrees help?
Otherwise, anyone need some 747 blades?

[YellowHammer]

747's do like a fast feed, and will resonate in softer wood and slower speeds.

Here is a video that shows the effects of sawing speed on cut quality, and I'm using a 747 band, which I prefer.  Your cuts are illustrated at about 10 minutes in. 

Yes, you can reprofile the bands.

[jpassardi]

I have seen the same YH.
I'm now using some EWP for B&B siding that I milled before I upgraded from 15 HP to 25 HP. I'm running into some of them that had similar chatter (wider cuts so feed had to be slower). With 25HP and 739's I'm now able to feed fast enough where I haven't gotten chatter since. I have also used some leftover 747's I have with more HP and don't recall seeing chatter.

[SawyerTed]

A roller guide bearing going bad or too little down pressure can sometimes allow the blade to resonate.  My LT35 had a period of persistent resonance like that.   Replacing the bearings in the guides and readjusting the down pressure resolved it. 

Cutting speed certainly has more to do with it than anything but it's a simple check and quick to make sure roller guides are good and in proper position.  

[YellowHammer]

Yes, I agree, and my video was based on the assumption the mill was dialed in, and I since I get so many questions about it, I figured I'd run the experiment in the video.    

[Stephen1]

Instead of circle sawmill marks on the wood, I recommend corduroy as the new fashion statement in rough cut lumber. Added value!

[customsawyer]

YH, I thought you was running 7/39 blades. Not 7/47.

[caveman]

He may have changed up on us without telling us.

[barbender]

Dang it, the rest of us will have to switch 747 blades if Yellowhammer did, because we wanna be cool like him! I don't want want to have to change everything up🤦

[YellowHammer]

Dang, you are 100% correct, I mis-typed...

I used to run 747's, now I run 7/39 almost exclusively.  I didn't like their "weak teeth".

Bartender, your coolness is always intact!!

[Larry]

So many variables, ya try different things and see what works.

For me the original WM 7/34 1-1/2 045 gives me a super smooth cut but leaves lots of sawdust on the board. I keep a few on hand. The 7/39 saws faster and also clears sawdust really good. It is a slightly rougher cut but good nuff for most things I saw.  It's my main blade. I gave the 7/47 a short trial.....nope they went to far, at least for me.

Kasco carries the same profiles but in 050. I can tell it gives me a slightly better cut than the WM just because its thicker. Not really enough to make a difference, I usually buy from whoever has the best price.

[barbender]

I wasn't overly impressed with the 7/47, especially with all of the hype WM pushed them out with. Or maybe because of it. I was really expecting them to be impressive, but they seemed to make waves more easily than 7/39s. 

I also couldn't understand how a 7/39 is only recommended for higher hp mills, but 7/47s were recommended for everything- and they're a more aggressive profile. Ah well, I guess I'm easily confused🤷

[customsawyer]

I tried one box of the 7/47s. I found that they cut well when sharp, but when they went dull they tend to mess up two boards. To be fair I only ran one box of them so maybe I was missing the signs they were sending me when they were getting dull. They didn't seem to improve much over the 7/39, and I had a good grasp on them, so that's what I use. 

[jpassardi]

747's do have a very narrow tooth with all that back cut. Logically - you'll get less sharpening's out of them so I only tried one box.
The more gullet (747) can carry more sawdust which is a positive. WM markets them as having faster sawing speed which makes sense.
I'm wondering if the chatter is due in part to tooth flex because there is so little material. Not sure it would cause band resonance though.

[Magicman]

I sawed over a million bf with 10° blades.  During that time, I experimented with several "trial" blades which included 9°, 7°, & 4°.  I even bought one box of 4° blades which were touted as being the cat's meow for sawing knotty, etc. logs.  I went on a job which was all Post Oak and started with a 4° blade.  Nope, so I put an old faithful 10° blade on.  Nope.  I had an unused trial 739 blade so I finally put it on knowing that surely it would not work on that hard Post Oak.  I learned a quick lesson that morning and immediately started replacing all of my reject blades with the 739's.  I never tried a 747 and never will.