Band tension

Larry · March 01, 2005, 03:45:23 PM

Gilman came up with an idea to check band tension last August right HERE. Checked the tension on three different brands of 10+ year old mills in good condition. On all three mills, the mill tension adjustment was way off. My mill was way low, 2nd mill was quite low, and the third was extremely high. After marking all three of the mill tension gages all of us saw improvements. With my mill I am getting better cuts in the half froze knotty stuff. The guy that had high tension on his mill is not breaking near as many bands.

We have been running the mills with our new tension settings in all kinds of logs for 6 months now...it was well worth the time to check the tension with the caliper.

Slack position with caliper at zero.

Proper tension somewhere in the 25,000 to 30,000 PSI range.

Thought I would post as might help somebody out.

Thanks for the idea Gilman!

PS....Don't ask me about the math....I flunked....ask Gilman!!

submarinesailor · March 01, 2005, 06:12:40 PM

Hey – I like this.

Now all we need is for someone to build a chart showing how much deflection we need with each blade size. Anyone out there want to volunteer? ??? ??? How about Wood Mizer's double hard 1.25" blades – aka my LT 15.

AtLast · March 01, 2005, 10:00:24 PM

My Baker uses hydo. band tension. Typically it runs around 1350lbs but varies on spiecies being cut..But can go as high as 1500lbs...I have found MOST of the time that the 1350 works well on all cuts....hope this helps

bberry · March 03, 2005, 06:32:29 AM

Larry, Good info! Should help people to tension. Can you give more info to help set up. What size is the measuring tool and how many thousands of change make up the correct tension. Thanks.

Larry · March 03, 2005, 12:48:42 PM

Click on the "Here" in my first post...it's a link that will take ya back to the original thread with the instructions.

Gilman · July 18, 2005, 12:15:12 PM

Larry,
Just cought up with this thread. Better late than never. :D

I'm glad the calibration helped out. 8)

If anyone has any questions about directly measuring your band tension, feel free to contact me.

WH_Conley · July 19, 2005, 10:06:28 PM

Sawed some pine today, results unacceptable. Not enough blade life without diving or climbing. Talked to my blade supplier, said not enough tension. Checked tension this way and shows guage is of by about 7500 psi. Cranked it up works fine now, can't wait to get back into poplar now.

lamar · July 19, 2005, 11:31:55 PM

if THAT IS A 6" CALIPER WHY SET IT AT 6" YOU CANT STRETCH THE CALIPER OR AIM i MISSING SOMETHING? :-\ smiley_confused I sure like this idea.Now a 1 1/4 7/8p about 150apx " what is avg. psi and by moving dial a couple thou. this is where tension should be? ??? thanks for the info and I would appreciate any more so I dont mess anything up.thanks again
"

Larry · July 20, 2005, 09:28:01 AM

My 6" caliper will over run about a 1/4" so I can use Gilmans formula that he figured out for 6".

I set it up for 5" and here is the formula.

Divide stress by Modulus of Elasticity. Multiply the result by 5" and that will give ya the measurement.

Example...you want 25,000 psi stress in the band. Divide that number by the MOE of steel which is 29,000,000. Result is .00086. Multiply by 5" and ya get .004 Since I knew I would never be able to remember all this math stuff I simplified it a little further and wrote on the side of my mill

.001 stretch = 6,000 psi strain @ 5"

This works for any size band or thickness of band.

Another thought...most of the numbers on your tension gauge are translations or just numbers without meaning. The only number we are interested in is the psi stress. Most bands will be in the range of 15,000 to 30,000.

Call the manufacture of the band you are using to find out what the recommended psi stress should be. I called Lennox for the Woodmaster C and was told 28,000. For the monkey bands seemed like they were about the same. The guy at WM didn't have any idea what I was talking about and I didn't pursue it, as only have a few of their bands. I,m sure they could give you the number...just have to get the right person.

D._Frederick · July 20, 2005, 05:55:49 PM

I may be wrong, but I think that formula is based on Gilmans using 1 1/4 inch blades. Some where in the figuring, the cross-sectional area of the band must be taken into account. A narrow blade takes less force to reach a stress level than a bigger, thicker blade.

Larry · July 20, 2005, 06:58:28 PM

D,
Thats where I got confused for a while. ??? Don't make any difference what the width or thickness of the band, the formula works the same way. We are looking at strain or stress in the band only...not the force required to get to that strain level.

Quote from: D._Frederick on July 20, 2005, 05:55:49 PM
A narrow blade takes less force to reach a stress level than a bigger, thicker blade.

Yes, the narrow band will take less force to reach the same stress level as a wider or thicker band but we don't care...the only thing of interest is the stress in the band.

Where is Gilman :

I'm sure he could explain it better than me...or maybe I'm the one that is confused. ;D

Gilman · July 20, 2005, 07:28:59 PM

You're correct Larry,

There's a linear relation between stress and strain in steel. The Modulus of elasticity (noted by the capital letter E) is the constant in the equation and for steel E is 29,000,000 lbs/in^2.

Stress = E x Strain

Hope this helps. If anyone has other engineering questions, feel free to contact me.

Daren · July 20, 2005, 08:23:28 PM

I can't take it anymore. I'm sure you guys are having fun playing with all the neat tools and equations , but really. Change the blade, and give it a "ting" with your thumb. You can tell by the sound how tight it is. If you get a miscut, make an adjustment. I may be way out of line here, I run a simple mill, sorry if I am being jerky. I have cut most species native to North America with a "ting" and have never been more that 1/16" off in 16', usually when I am getting dull. Never broke a blade and believe I get my moneys worth out of them bft wise , they only last so long no matter what(unless I hit a nail). I love this board because most everyone is very positive and fun, and I don't want to step on any toes. Sometimes I just have to call b.s.. I was always told "If you can't say something nice don't say anything at all". I promise I will do that next time.

Dan_Shade · July 20, 2005, 10:21:22 PM

some of us are just technical weenies, Daren! I pretend to be, but often go for the "close enough" method :D

the engineer in me does like this method, though, it's simple and easy to duplicate. I need to call up timberwolf and see what their specs are.

lamar · July 20, 2005, 11:37:26 PM

This is great.Now I tested this out (red streak blades) set my caliper at a little less than 6" but used mini bar clamps(lighter and less strain on caliper) now here is the funny part,my mill has a 5/8 threaded rod no spring and maybe a 1/4" support plate to tighten nut against.I proceeded to tension till I could see dial move.I normally set tension with a torque wrench at about 20lbs This seems to work OK but always wanted to know the truth.I got up to around 35 to 40 and nothing moved except the support plate(now I will need to weld some angle braces to keep it still.This the only mill I know so It seems like the band is awful tight but still haven't seen any stretch.Will over tightening cause trouble with bearings?By the looks of my test so far I'm way under tension.Am I right that you have to get a little stretch to get blade to track properly?

Smakman · July 20, 2005, 11:58:59 PM

I broke a blade and went through two sets of blade guide bearings in one day and I finally came to the conclusion that I was running the blade too tight. I may have to do a little experimenting on the height of the bearings vs. blade tension too.

Furby · July 21, 2005, 12:08:54 AM

Well I'm simply going to say that I'm happy with my setup, and am only running a small fraction of the tension you all are talking about.........without problems.
If it ain't broke........don't break it! ;) ;D

Fla._Deadheader · July 21, 2005, 06:45:31 AM

I'm witchyu, Furby. ;) ;)

GF · July 22, 2005, 08:58:30 AM

Furby, FDH I am with you on this also. I run enough tension to keep the cut straight, more tension on steel than needed will cause metal fatigue and failure.

Fla._Deadheader · July 22, 2005, 09:42:39 AM

Engineering is nice. I just do what works for me, and pass the info along. It just might help others. Our trailer tire mill is a different animal, so, I go along with most of what's said. ;) Mostly. :

:

:D :D

Just for kicks, we are going to try this, IF I can remember to take the caliper and clamps to the mill. :

:

;D ;D