top side of blade vibrating

postville · March 18, 2011, 07:46:38 PM

What does it mean when the top side of the blade is vibrating and hitting the spacer bolt on a LT40? I am in the yellow to orange tensioner setting. Pulley B57 belts are about 100 hours of use. Using Cook's blades 8 degree set, basswood logs.
Bob

Faron · March 18, 2011, 07:58:24 PM

Did you look for a sawdust clump under the belt?

tyb525 · March 18, 2011, 07:58:43 PM

This might help:

https://forestryforum.com/board/index.php/topic,7789.msg106444.html#msg106444

POSTON WIDEHEAD · March 18, 2011, 08:16:12 PM

Postville, my LT 40 was delivered to me 1 month and 9 days ago. The guy that set it up and taught me the basics of my Lt 40 is a rep. for woodmizer. He told me not to worry about the yellow and orange on the psi gauge. He ran the pressure up between 2800 and 3000. I have been milling it that way ever since and get no viberation. It's a smooth cut also.
May want to try yours at this pressure.
David

PS. I use woodmizer blades at this psi. Also like Faron said....look for a sawdust clump under he belt.

northwoods1 · March 18, 2011, 08:57:06 PM

When I bought my LT40 the dealer advised me to keep the tension way up like that also. Not quite up to 2800-3000 but it was off the orange scale when idling and when sawing it just came back into the orange.
I have experimented with cutting at a much lower tension and can not notice any difference as it cuts perfectly and smoothly as long as the blade is sharp and the feed speed is not to fast. Now I normally keep the tension way down, about just so it is in the yellow or slightly below. I think that it would help with getting more life out of the bands.

Chuck White · March 18, 2011, 09:34:20 PM

Adjust the throat bearing to within 1/8 inch of the blade with tension applied.

That bearing is nothing but a plastic bolt with a lock nut on it, and it is supposed to prevent blade flutter.

I also saw with the tension gage above the orange scale.

tyb525 · March 18, 2011, 09:41:13 PM

In the link I posted, Tom mentioned using a wooden block in place of the bearing. I did the same thing on my mill, it works great.

Brucer · March 19, 2011, 01:33:50 AM

What it means is the blade is being vibrated by something at very close to the blade's natural frequency. That screw is supposed to damp out some of the vibration when the blades starts to hit it -- otherwise your blade will self destruct in a hurry.

The blade's natural frequency depends on:

The length of unsupported bladed (basically wheel-wheel).
The tension of the blade.
The weight of the blade.

This list is exactly the same as the tuning for a guitar string (or fiddle, mandolin, banjo, etc.). The string vibrates at its natural frequency. If you've ever tuned one you'll have a pretty good feel for what's going on with the band. About the only thing you can change there is the tension.

There's several things that can cause the blade to vibrate at a certain frequency:

Speed of the blade.
Number of teeth on the blade.
Width of the cut.
Bumps on the bandwheel (e.g. sawdust).
Bad bearing on a bandwheel.
Something sticking to one spot on a blade guide roller.
Vibration from the engine or anything driven by the engine.
And a bunch of other stuff I can't think of right now.

Sometimes pushing the blade a little too hard can increase the amount of vibration. This is especially true with soft wood and hard knots.

Try a higher tension, look for sawdust lumps under the bandwheels, try cutting different material or smaller logs ... basically try stuff and figure out what makes it go away.

bandmiller2 · March 19, 2011, 07:16:19 AM

Sometimes the loose belt system will start the blade vibrating,the slack comes around and wacks the band.Sometimes you just get it no matter what you do,don't think a little does any harm. Frank C.

Peter Drouin · March 19, 2011, 07:29:00 AM

use woodmizer blades on a woodmizer sawmill not some junk blade. cleen out the sawdust and bring the tension up, a woodmizer blade can take it. 8) 8) 8)

ladylake · March 19, 2011, 07:29:45 AM

Learn a few new words and try a B56 Goodyear belt. Steve

postville · March 19, 2011, 09:05:42 AM

Thanks all for the replies. I have the picture now.
I'll let you know on Monday after I make the modifications how things go.
I am feeding as hard as the motor will take it, maybe less is more in this situation. I lost 45 minutes messing around with repairs on Fri. Probably would have gotten more done by easing up on the feed.
I am still trying to get things going like when I had my circle saw rig. Now sawing with 1/4 the horsepower so I can't expect to chew up logs like in the past. Bob

pa_of_6 · March 19, 2011, 09:28:42 AM

Quote from: Peter Drouin on March 19, 2011, 07:29:00 AM
use woodmizer blades on a woodmizer sawmill not some junk blade. cleen out the sawdust and bring the tension up, a woodmizer blade can take it. 8) 8) 8)

Pete, your opinion that Cook bands are junk blades is just that, an opinion, and it should be kept to yourself.
Cooksaw and the fine people that operate that business do a very good job and are very informitave and knowledgeable.

I have cut a couple million board feet with Cooksaw bands on a Woodmizer mill and have found them to be excellent bands.

Woodmizer should be able to have told postville what he needed to do to solve his problem, which is probuably as siimple as adjusting the bolt that limits the flutter , that is why it is there.

As for woodmizer reps telling their customers to increase the tension on their bands to well above what factory recommondations, it just shows the lack of understanding on how the bandsaws are designed to cut.

Woodmizer does not pay their engineers thousands of dollars a year to figure this stuff out just to have some salesman who has never made a living cutting logs tell their newbie sawyer not to listen to what the engineers figured out.
Well I guess he will sell more bands to you if you stretch the the crap out of it and it breaks sooner...but I guess he is padding his pockets and puttin shoes on his kids feet...or buying a fancy new truck to drive around in to sell mills and bands.

sdunston · March 19, 2011, 11:13:24 AM

Postville;It sounds to me that the blade might be a little lose, I have used blades from Cooks and have had no problem.I think Cooks blades tend to be off a little in length as WM is consistent.Blade tenision is the key to good sawing and without a blade tenision gauge its hard to tell.JMO
Sam

Peter Drouin · March 19, 2011, 08:19:35 PM

Pa-of-6 thanks for your opinion on cook blades. Im sure there ok blades. do they make them ? I have done the millions thing too. have been with wm over 20 years on my 3 rd mill. I have talk to the (engineers) face to face and I understanding the blade thing. you have to remember the safety thing. today its all about the safety thing. so the book says one thing and in real life tighten the blade up . And I dont think the wm salesmen would lie to you so they could buy a new truck. I buy parts and blades from wm. they keep me working I keep them working just the way I am. And as for keeping my opinion to myself I still think we have freedom of speech in the USA Happy cutting to all 8) 8) 8) 8) 8)