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Author Topic: lbs of tension on your bands  (Read 4612 times)

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Offline New Brunswick

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lbs of tension on your bands
« on: April 27, 2008, 05:52:09 AM »
   What are some of you guys running for tension on your bands, I have been using red streak bands but am switching to woodmizer, I asked the fellow that took my order and he recommended 2500 lbs.

Offline Dan_Shade

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Re: lbs of tension on your bands
« Reply #1 on: April 27, 2008, 06:46:37 AM »
what's your mill?  I have a woodmizer LT40HDG25 and I crank the gauge over to 2800 or so.  but I have no scientific proof that it should be that.  it's  just what I do.
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Offline John Bartley

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Re: lbs of tension on your bands
« Reply #2 on: April 27, 2008, 07:28:01 AM »
The tension that you show on a gauge at the tension control is going to depend on the size of the blade and the diameter of the piston or tension rod that you have. When you measure blade tension, what you're really measuring is the strain on the band. The manufacturers have a "strain" specification for their bands and if you dig deep enough, they'll supply it for you. I'm using Hakkansen bands, sold in Quebec as "MillMaster" and (as far as I know) from Suffolk as"Timberwolf", and the strain at the band is supposed to be approximately 18,000lbs. On my gauge I show 1250-1300psi. There are a couple of very good threads here at FF regarding "strain" and how to measure it by measuring the amount of band stretch.

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Offline Dave Shepard

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Re: lbs of tension on your bands
« Reply #3 on: April 27, 2008, 10:34:24 AM »
I was told by the Wood-Mizer person who delivered the new mill to run around 2800 psi. We are running the .055's, but I think he said to run the other bands up there too.


Dave
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Offline Tom

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Re: lbs of tension on your bands
« Reply #4 on: April 27, 2008, 10:40:22 AM »
The fellow that took your order knew what he was talking about.  The woodmizer saws measure tension with a hydraulic pump and the recomended preassure on the gauge has been 2100 lbs since about 1989.

The fresh .042 band is brought to 2500 lbs and allowed to "seek" 2100 as it warms ups.   Some guys found that it ran better at 2500 lbs a would leave it there.   Eventually woodmizer began saying that 2500 lbs was the way to go.

I got good results at 2100 lbs and decided that the less tension the easier on the saw, so I never changed.  But it made me feel better that I could crank it on up there, if I wanted more tension, without worrying about it.

Those Woodmizer Customer Service guys won't feed you a line just to give you an answer.
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Offline Dave Shepard

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Re: lbs of tension on your bands
« Reply #5 on: April 27, 2008, 10:44:13 AM »
Tom, that's about where the gas Mizer I was running wanted to be. I'd start at the high side of the orange, and it would always settle just on the line between the orange and yellow. Those were the .045's. The .055's on the Super definately want to be up around 2800, if it drops much below that I can tell by the cut quality.


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Offline eamassey

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Re: lbs of tension on your bands
« Reply #6 on: April 27, 2008, 11:49:59 AM »
I am building a mill and and blade tensioning is about next.  So this thread is of considerable interest to me.  Comments:  the 2100#, 2500#, etc. are strictly for Woodmizer design, as it is a hydraulic pressure value.  The real value is at the blade itself, and the values mentioned in older posts were 25,000 psi tensile on the blade (25,000 psi = about 2000# actual tension on a .042" x 1-1/4" band blade - the sum of tension on the lower and upper leg of the blade). It should not matter how you get the blade tension, hydraulic, mechanical, etc.  In the Cook's catalog, there is mention that the tensioning system should incorporate a spring, so as to compensate for band length growth as the temperature rises.  That seems right to me----anybody able to comment on this?
Second--- my current tensioning idea is to use an 0-100 psi AIR cylinder, getting the needed multiplication through mechanical leverage.  (An air cylinder, like a spring, can respond to temperature elongation, stretch, wear.)  Anybody tried this and/or have comments?
Third--- Has anybody seen or tried blade tensioning by other than the two wheels?  Think high-track Caterpillar, although if I try this I might do 4 smaller wheels on a walking leg setup.
What does anybody think??

Offline Dan_Shade

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Re: lbs of tension on your bands
« Reply #7 on: April 27, 2008, 12:01:11 PM »
I'd be concerned with the bend radius and tracking of the bands if a 3rd wheel was added.
Woodmizer LT40HDG25 / Stihl 066 alaskan
lots of dull bands and chains

There's a fine line between turning firewood into beautiful things and beautiful things into firewood.

Offline LeeB

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Re: lbs of tension on your bands
« Reply #8 on: April 27, 2008, 12:23:54 PM »
Where you gonna get air from. I suppose one of the small 12volt compressors would work for you.
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Offline eamassey

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Re: lbs of tension on your bands
« Reply #9 on: April 27, 2008, 04:40:19 PM »
In reply to LeeB -- "Where you gonna get air from?"
     This is a stationary mill, electric powered.  I have another use for air-- I have an air clutch.  The air will be brought in by a 1/8" air line, on festoon system with the electric service, also with a small buffer (accumulator) tank on the saw head carriage.

In reply to Dan_Shade --- on bend radius, I can do pretty good on the radius with several small wheels- I would also crown the wheels to assist tracking.  Don't know how good it would work. Another possible down side is that it would slightly reduce from 180 degrees the contact on the drive wheel.

Offline Tom

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Re: lbs of tension on your bands
« Reply #10 on: April 27, 2008, 04:46:10 PM »
This Forum is as deep as the Mariana Trench.  Start searching and you will find a lot of info on this subject.

Here is a thread to start with.

http://www.forestryforum.com/board/index.php/topic,7923.msg107524.html#msg107524

 :)
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Offline Jeff

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Re: lbs of tension on your bands
« Reply #11 on: April 27, 2008, 06:21:41 PM »
I've been setting mine about 2300  and dont worry about it again unless it drops to below 2100. I think this probably comes from direct advice from having Tom beside me on the first larger log I sawed.
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Offline ADAMINMO

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Re: lbs of tension on your bands
« Reply #12 on: April 28, 2008, 12:11:16 PM »
Wether you want to use springs , air cylinders , air bags , hyd. cylinders , or other means makes not much difference. We have used all the methods above and find that the hyd. cylinder works best on a sawmill.For resaws we use a spring because it is cheaper and just as reliable. The key is getting the proper strain tension for the band you intend to use.On our older multi head resaws we used air bags for blade tension. It was a closed air system so a air tank worked well. We would used 90 psi of air pressure to apply the proper strain on the blade , the key was having the proper length spacers at the air bag to tension up to and have the proper strain on blade.
 When you go to using more than 2 wheels on your blade set up then it is alot harder to track the blades and keep all wheels on the same plane.You also pose a problem as mentioned before about your bend radius. I don't know if any of you remember the Baker Bangsaw .... It was available in a 2 or 4 cut configuration. The blade life on these machines were reduced tremendously due to the bend of the blade as went through the 4 wheels.It was configured to where one blade ran on 4 wheels and made 2 cuts or 2 seperate blades ran on 4 wheels each and made 4 cuts. Blade life was cut in half and it was a bear to keep tracked.
 I don't know how to make those fancy drawings but hopefully you can understand my description of how the blades run.  I made this drawing and scanned it in so you would understand.Sometimes I don't explain things very well.



( Sorry ..... Forgot to rotate the pic before uploading.)

Offline WILDSAWMILL

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Re: lbs of tension on your bands
« Reply #13 on: May 07, 2008, 10:30:59 PM »
my Kasco saw2B runs 600-800 lbs
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Offline MartyParsons

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Re: lbs of tension on your bands
« Reply #14 on: May 08, 2008, 05:51:15 AM »
Quote
Second--- my current tensioning idea is to use an 0-100 psi AIR cylinder, getting the needed multiplication through mechanical leverage.  (An air cylinder, like a spring, can respond to temperature elongation, stretch, wear.)  Anybody tried this and/or have comments?

Look at the Wood- Mizer LT70 Design we use a air blader like on a truck axle suspension. These work quite well. They have changed this design a few times through out the years. The latest and greatest has both the Air and hydraulic. The air works well because it does not need adjusted once the desired tension is achieved. Set the air pressure to 75 psi then pull the handle and saw.
I always run the mills with the band tight, a little above the Orange mark on the gauge 2500 psi. Some band maufactures ( other than WM blades) do not run their blades that tight.
Hydraulic tensioner changes with the length of the blade on the LT40 models and adjustment is needed. Heat, sawdust build up on the wheels, blade condition, sawing speed and other factors effect the blade tension. I always train owners to use the gauge as a tool while sawing. If the gauge changes while in the cut something has effected the blade temp.
Hope this helps!


Marty
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Offline mike_van

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Re: lbs of tension on your bands
« Reply #15 on: May 08, 2008, 05:39:03 PM »
Just my 2 cents on air - Down south you're probably fine, up north, air is the last thing I want to mess with in the dead of winter. We used to have air drills in the bucket trucks, even draining the tanks everyday, winter was a pain in the butt. Guys would thaw out the tank valve with a road flare, or drill by hand. When they went to hydraulic tools,  it was like NASA technology came to the power company  :D
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Offline eamassey

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Re: lbs of tension on your bands
« Reply #16 on: May 08, 2008, 11:10:00 PM »
Thanks to MartyParsons and Adaminmo.  Your knowledge of what has been done before and how well it worked is really important to someone like me. 
Specifics---  Marty, you say "The latest and greatest has both the Air and hydraulic".  I take it this is air-over-hydraulics. 
                  Adaminmo--- your sketch was adequate for understanding how the system worked.  My understanding of fatigue life is that every bend hurts--- with the effect a function of bend radius along with degrees in contact---- but with any reverse direction flex to be two or three times worse than unidirection flex. 
                mike_van--  I am an experienced air and hydraulics user.  They both have their own problems.  But most every factory in the country uses some of both of them. 


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