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Author Topic: dynamic or static tension  (Read 980 times)

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Offline charles mann

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dynamic or static tension
« on: August 04, 2019, 02:26:44 AM »
ok, i did a search and might not have used the proper verbiage in the search engine, but i spent a while looking through the topics and only came across 1 guy @milhead talking about dynamic spring tensioning, but nothing from him since oct of last yr with his build. 

i do see on some of the WM mills (lt15), they use a spongy plastic disk that gets compressed when the band is being tensioned. I'm assuming that plastic acts as a dynamic tensioner, but could be wrong.

instead of copying the mill builder's plans, yet he even thought about adding a spring tensioning system on his next mods to his mill. I want to use use a tensionmeter, spring, big bolt, indicator marking and a torque wrench to set my blade tension according to manufacturer's specs for the blade. i will use both kasco and wm for my bands (1 1/2" or 2" x 306" or 308", 7° for starters) and I'm sure each of them have a different tension requirement. 

question. would it be better to go with static or dynamic tensioning on that big of a blade?
other than using a tq wrench, how would a person calculate the amount of tension (in ftlbs) by using the tensionmeter and the lbs of force required for tensioning? 

if its gonna be LOT of ft lbs, i may scrap the tq wrench method, but still use everything else and verify with the tension every couple blade changes initially, then maybe every 10-15 changes, just to ensure the spring isn't weakening over time.

granted a hydraulic ram (port-a-power, or short stroke horizontal bottle/floor jack) with a psi gauge could greatly minimize the need for using the tensionmeter, but its 1 more thing to worry about, throwing a temper tantrum and sending very sharp things at very high speeds everywhere. but so could a spring, which is why I'm asking is dynamic would even be a logical method of tensioning. 

thanks in advance fellers. 
Temple, Tx
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Offline scsmith42

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Re: dynamic or static tension
« Reply #1 on: August 04, 2019, 08:52:53 AM »
Charles, keep in mind that when a band is in the cut, it heats up and expands - thereby decreasing tension unless you have some type of system that is designed to maintain proper tension even when the band expands.

Baker uses a hydraulic accumulator in order to maintain a constant pressure on the band.  I’m not sure what the other brands use.

Scott
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Offline Southside

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Re: dynamic or static tension
« Reply #2 on: August 04, 2019, 10:02:54 AM »
My 35 has the squishy ball and it works OK, my 70 has an air bag which is compressed by a hydraulic ram, the bag  becomes a dynamic tensioner at that point and it works well, the gauge never moves.
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Offline Dana Stanley

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Re: dynamic or static tension
« Reply #3 on: August 04, 2019, 11:04:08 AM »
Norwood, and Woodland use a compression spring between the T handle and frame. I torque mine to 25 lbs, and I guess the spring keeps it there when the blade heats up.
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Offline charles mann

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Re: dynamic or static tension
« Reply #4 on: August 04, 2019, 12:16:17 PM »
Charles, keep in mind that when a band is in the cut, it heats up and expands - thereby decreasing tension unless you have some type of system that is designed to maintain proper tension even when the band expands.

Baker uses a hydraulic accumulator in order to maintain a constant pressure on the band.  I’m not sure what the other brands use.

Scott
which is what lead me to my question. i was thinking of going dynamic for the reason you stated, just rarely see them used in home made mills. i guess the car tires and the belted pulleys work as a dynamic system
now i need to find out how to calculate the 1000s of psi on the tensionmeter reading, to actual (close to actual) ft lbs of load/ tq/ tension/ compression. 
a 1 ton compression load cell in 10 lb increments and a bottle jack could help me with that, but iv never seen a load cell for rent, and the cost of that thing is EXPENSIVE.
 I'm sure there is a formula out there. when i contact kasco again to order my first 5 blades, ill ask if there is a formula. but i was hoping someone here knew of 1, so i could get a guesstimate of the force required, and start researching springs like Dana Stanley linked to, or a hydraulic accumulator as you mentioned. maybe could even find a couple squishy balls like southside mentioned. 
thank you all for your replies, and the confirmation of using a dynamic tensioning system. 
Temple, Tx
Fire Fighting and Heavy Lift Helicopter Mech
Helicopter and Fixed Wing Pilot

Offline Pabene

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Re: dynamic or static tension
« Reply #5 on: August 04, 2019, 01:30:24 PM »
You have to have a spring in your system. It is also good to have the spring close to the wheel shaft so you can get minimum weight of the parts as will move if a piece of bark or wood suddenly are pinched between the blade and wheel. When I bought my mill the tension system was hydraulic, a hand pumped syst with a guage. If something went in between blade and wheel during a cut, the saw frame had to act as a spring. It resulted in deformation of the frame so the tracking was disturbed for each time it happend. To create the force a hydraulic jack is very good but you need a "spring element" in serial. Woodmizers pneumatic solution looks good. I have written on this forum before about tension. You can check you are in the right aria if your jack can give a force to prolong the blade, like a rubber band, 1/1000 of the length you are checking. It is a simpel tension test method as will work for all types of steel blades. So far I know most of the blade manufactures reccomends their blade to be tensioned to about 10% of the tension when the blade would break.

Offline charles mann

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Re: dynamic or static tension
« Reply #6 on: August 04, 2019, 05:30:25 PM »
thank ya'll for the info. after searching through pabene's post, it lead me to another, then to another, which im sure after reading through it, will lead me to another. those that iv read through so far have given me a lot of ideas, and im not sure who said it on 1 of those post, but use acme rod instead of a bolt, less friction and a higher load rating. just gotta find me some compression springs that would possibly end up with a 1300 lb compression rating, if my math is correct from a 1 of those other posts.

I truly enjoy this site with the combined knowledge of everyone.
Temple, Tx
Fire Fighting and Heavy Lift Helicopter Mech
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Offline Steve Crook

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Re: dynamic or static tension
« Reply #7 on: August 04, 2019, 06:13:17 PM »
there is a post on utube that shows how to measure band tension by measuring the stretch of the band. it is on A very ordinary man channel.  he gives the formulas for calculating the stretch. it is the second part of the calculation that is critical. I obtained the spring on my build from cooks. I think he sayed it is a 1400 lb spring. My mill is a lynn knockoff . I have been meaning to post some picks of it now that it is close to finished buy havn't sat down and figured out how to post the build picks. 

Offline Southside

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Re: dynamic or static tension
« Reply #8 on: August 04, 2019, 06:17:50 PM »
One other point to keep in mind is the effect the band tension will have on your wheel bearings and axle. Just make sure they can handle the lateral load. 
Franklin buncher and skidder
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Riehl Edger
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Offline charles mann

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Re: dynamic or static tension
« Reply #9 on: August 04, 2019, 07:32:35 PM »
One other point to keep in mind is the effect the band tension will have on your wheel bearings and axle. Just make sure they can handle the lateral load.
my shaft is a 3" 4140, turned down to 2.5" for the bearings, drive pulley, then down to 2" for the diving band wheel. the bearings are rated for 46,500 lbs oF dynamic force and 62,500 static, and I have to 2. Im hoping that is enough.
Matt Cremona, the guy I got his build plans from, used 4 pillow block bearing, with a 2" shaft. I think my cut width is about 6" wider than his, so IM THINKING I SHOULD BE GOOD.

PLUS MY IDEL SIDE IS A 2" SEALED BEARING, AND ITS WORKING FOR HIM SO FAR.
Temple, Tx
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Offline Southside

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Re: dynamic or static tension
« Reply #10 on: August 04, 2019, 08:01:05 PM »
Oh good - well you should be able to wrap it right up then, I mean after all his friend there in Texas made one in what 4 days?  :D
Franklin buncher and skidder
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Offline ljohnsaw

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Re: dynamic or static tension
« Reply #11 on: August 04, 2019, 08:45:44 PM »
I'm not sure who said it on 1 of those post, but use acme rod instead of a bolt, less friction and a higher load rating.

Not sure if you had read my post or a post I made on another.  I used an acme thread from a scissor jack.  Regular threads are meant for holding and you will wear them out QUICK.  An acme thread has a larger contact surface with the square cut threads.  Just keep it greased well.

My mill is dounut spare tires (rounder profile so tracking is better, less chance of taking the set out of the band) so there is some "give" with air.  I did give it a try putting a spring in line with the acme threads.  Turns out it wasn't enough of a spring - too weak - and I had to collapse it all the way to get the tension I needed.  So I took it out.

As far as having to withstand the tension forces, bearing on both sides of the band would be the best and would tend to hold the tracking the best.  I went a different route and used car hubs.  I took rear hubs off a front wheel drive Toyota.  I figure they should too quite well and they have.  The one mistake I made was to disassemble one to get my drive pulley mounted behind the hub and I didn't get it tight enough when I put it back together (didn't have an impact back then) and it failed.  No damage but was down for a bit.  Found a second hub and just had to figure out a different mount for the drive pulley.
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Offline charles mann

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Re: dynamic or static tension
« Reply #12 on: August 04, 2019, 09:53:17 PM »
@ljohnsaw  if you have to disassemble the hub again and don't have an impact, use a long pryer, bind it against 2 wheel studs and the ground and start yarding on the ratchet/breaker bar. i had to do that in ankle deep water, with a plastic bed liner over the fender well of my 06 dodge when the 4x4 hub crapped out. luckily, i knew how to do it from my 01 dodge and the same side 4x4 hub crapping out on it. 

and yes, it was your reply/topic talking bout the acme rod/nut from the scissor jack. with the tension I'm possibly gonna need, i think a 1" acme rod and 4 die springs should provide enough even tension.


 @Southside yea right. there were 5 of them, she had her material precut, and used nearly the same setup. not knocking her build, but i do spend more time away from home, do 99.99% of the work myself with no help and the machine shop took "no rush" literally, taking over 5 months to do a 2 day job, and im still not sure if its done. i also plan to make my mill portable, so an electric motor is out of the question. 
Temple, Tx
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Offline charles mann

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Re: dynamic or static tension
« Reply #13 on: August 04, 2019, 09:55:18 PM »
there is a post on utube that shows how to measure band tension by measuring the stretch of the band. it is on A very ordinary man channel.  he gives the formulas for calculating the stretch. it is the second part of the calculation that is critical. I obtained the spring on my build from cooks. I think he sayed it is a 1400 lb spring. My mill is a lynn knockoff . I have been meaning to post some picks of it now that it is close to finished buy havn't sat down and figured out how to post the build picks.
ill do a youtube search and check it out. do you by chance have the part number of the spring you used from cooks? 
you still in the helena area?
Temple, Tx
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Offline Southside

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Re: dynamic or static tension
« Reply #14 on: August 04, 2019, 10:15:07 PM »
Don't forget unlimited funding and sponsorship helped quite a bit too. 
Franklin buncher and skidder
JD Processor
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Riehl Edger
Woodmaster 725 and 4000 planner and moulder
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Offline charles mann

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Re: dynamic or static tension
« Reply #15 on: August 04, 2019, 11:06:52 PM »
Don't forget unlimited funding and sponsorship helped quite a bit too.
I WASNT AWARE OF THAT, BUT I GUESS THAT HELPS TOO. I HAVE UNLIMITED FUNDING TOO. I JUST HAVE TO SAVE UP FOR IT AND DO IT IN SPERTS. IM UNLIMITED TILL I RUN OUT, THEN HAVE TO SAVE UP AGAIN. CRAPPY PART IS, I HAVE MORE FUNDING THAN I HAVE TIME.
BUT IN HER BUILD TIME, IT HELPS HAVING EVERYTHING PRECUT, PERSONNEL ONHAND AND FOLLOWING THE PRINT TO THE LETTER. BUT I BET SHE WONT BE MOBILE EITHER, SO I'LL HAVE THAT ADVANTAGE. I MEAN COME ON, HOW MANY 76" CUT WIDTH MOBILE MILL ARE THERE OUT THERE?   :D
Temple, Tx
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Offline Southside

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Re: dynamic or static tension
« Reply #16 on: August 04, 2019, 11:13:55 PM »
FWIW I had to replace the carrying rod on my Lull that the forks ride on and I used a piece of 2" 4140, I have had 6,000 lbs on the forks and the rod has not shown the slightest bend, dent, scratch, etc and the supports are about 20" apart, so you should be fine with that set up.  
Franklin buncher and skidder
JD Processor
Woodmizer LT Super 70 and LT35 sawmill, KD250 kiln, BMS 250 sharpener and setter
Riehl Edger
Woodmaster 725 and 4000 planner and moulder
Enough cows to ensure there is no spare time.

Offline charles mann

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Re: dynamic or static tension
« Reply #17 on: August 04, 2019, 11:17:16 PM »
there is a post on utube that shows how to measure band tension by measuring the stretch of the band. it is on A very ordinary man channel.  he gives the formulas for calculating the stretch. it is the second part of the calculation that is critical. I obtained the spring on my build from cooks. I think he sayed it is a 1400 lb spring. My mill is a lynn knockoff . I have been meaning to post some picks of it now that it is close to finished buy havn't sat down and figured out how to post the build picks.
WELL, I FOUND THE GUY, AND I REMEMBER WATCHING A FEW OF HIS VIDS, BUT DIDNT COME ACROSS THAT PARTICULAR VID. I TYPED THE FORMULA OUT WITH EX. FIGURES, BUT IF BY THE OFF CHANCE, MOST BANDS, AT TENSION MOVE ABOUT 0.010-.015, THEN MY PSI IS POSSIBLY WAY LOW (9,860 PSI), WHICH INTURN, MY LBS OF FORCE SHOULD BE LOW (1,035 LBS) TOO.
IDK THOUG, BUT WHEN I GET MY BLADES, I SHOULD KNOW BEFORE THEY ARRIVE, WHAT THE RECOMMENDED TENSION PSI IS, WHICH SHOULD ALLOW ME TO INPUT THE CORRECT NUMBERS TO GET THE CORRECT LBS OF FORCE. THEN I'LL BE HAPPIER THAN BACON BEING SPRAYED WITH THE WATER HOSE IN THE SUMMER, AND CAN ORDER UP THE CORRECT DIE SPRINGS. 
Temple, Tx
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Offline charles mann

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Re: dynamic or static tension
« Reply #18 on: August 04, 2019, 11:22:27 PM »
FWIW I had to replace the carrying rod on my Lull that the forks ride on and I used a piece of 2" 4140, I have had 6,000 lbs on the forks and the rod has not shown the slightest bend, dent, scratch, etc and the supports are about 20" apart, so you should be fine with that set up.  
COPY THAT. I LISTENED TO THE MACHINIST AND WENT OFF HIS RECOMMENDATION, AND EVEN THOUGH THE COST OF MATERIALS WILL BE HIGHER THAN GOING WITH 2" ALL THE WAY AROUND. THE INITIAL COST IS CHEAPER THAN HAVING TO BUY EVERYTHIGN AGAIN AND PAYING FOR THE MACHINE WORK AGAIN. I THINK IF I HAD TO DO THAT, ID SCRAP THE MILL, SELL THE MOTOR, USE THE BAND WHEELS AS A BOAT ANCHOR, SET FIRE TO THE REST OF TREES THAT WOULD NEED MILLING AND CALL IT A DAY.
BUT THANKS FOR THE KIND WORDS OF POSSIBLY HAVING ENOUGH SPINE INT HE DRIVE SET UP. I TEND TO OVER BUILD THINGS, JUST SO I DONT HAVE TO BUILD IT AGAIN, EVER AGAIN. IF 1/4" WOULD WORK, I WANT 1/2".  
Temple, Tx
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Offline MAF143

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Re: dynamic or static tension
« Reply #19 on: August 05, 2019, 02:35:35 AM »
Our mill uses a series of 5 or 7 conical spring washers (belleville washers) back to back, front to front on the tension shaft.  I'm not sure what the threads are on the shaft without tearing it apart, but maybe you could call Woodland and order some of their washers?

It seems to be a down and dirty solution, but seems to work.  Torque to 25 lb. ft. and it's up and running.  Their is a diagram in the manual, but I don't have the manual here to post a pic of it.  I know there is a diagram of them in the manual, cuz when I was assembling it, being the curious type, I took all that stuff apart to see how it all works.

Let me know if you need some pix or measurements or anything.  I don't always get on here everyday but I'll try to keep an eye on here if you want more info on that setup.
Always having a great day!
MS 391, MS 250, HM-126, Ferguson TO-35, '97 Ram 1500 wood cuttin' truck, splitter, Woodland Mills Grindlux 4000 sharpener, Vogelzang Ponderosa keeping us warm


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