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Author Topic: dynamic or static tension  (Read 981 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.

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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
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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
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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. 
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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.
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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
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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. 
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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?
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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. 
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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
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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.  
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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".  
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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!
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Re: dynamic or static tension
« Reply #20 on: August 05, 2019, 07:31:36 AM »
Belleville washers are good. You have to use a number of the washers so the package of washers will be about 3 " long. The spring function in this washers is rather steep, the force to compress a washer increases quickly. You can also adjust the compress force with this washers by to put them together in the package so two (or more) is turned back to front, next group front to back and so on, it will dubble the force. To have an suitable function in your mill you need a remaining springstroke of 0,5" when you have the blade under tension.

Offline Steve Crook

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Re: dynamic or static tension
« Reply #21 on: August 05, 2019, 09:52:21 AM »
      the spring I got from cooks is a 133-012 spring bandmill yellow 1400 lb. there cost was 30.dollars. I made a holder for a digital caliper that covers 2 foot. on my thought that it will be more  accurate over a longer distince than the ones that span a fiew inches. 
     yes I am still in the Helena area. Are you in The area on our fires?
    

Offline charles mann

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Re: dynamic or static tension
« Reply #22 on: August 05, 2019, 12:39:51 PM »
@MAF143 if you don't mind, maybe a part number for them and ill do a google search and see if i can come across something online to see if it would work for me. thank you for the info. 

@Steve Crook thanks for the p/n, once i get a more accurate requirement for my blade, ill try the different recommendations and se which will work best.
naw, not up there, stuck in colorado again this yr. our sister ship is based out of helena, but is in missoula right now. if i end up on that machine next yr and we actually start our season off in helena, ill give you a shout and try to swing by. 
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Re: dynamic or static tension
« Reply #23 on: August 05, 2019, 03:28:37 PM »
If it isn't raining when I get off work, I'll walk out to the mill and get the manual and some info for you.  Unfortunately the thunder rolls at the moment...

I'll take the calipers and get some measurements and pix.

scuba-smiley electricuted-smiley
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Re: dynamic or static tension
« Reply #24 on: August 05, 2019, 05:03:08 PM »
Kinda glad it was raining.  Even better info this way all except the thread dia and pitch.

Woodland Mills has the Operators manual on their website.  Pages 57 and 68 have nice diagrams of the belleville (part 164 in the list) washer stack and the parts list is in there too.

There are other washers and a thrust bearing in the build stack for the tensioner too.  Tension handle is part 20 but doesn't give the threads.  Blade info is part 46.  Part 19 tension bar doesn't give the thread size or pitch either.  I would think the thread size and pitch along with the 25 #' of torque for that blade size info would get you to a close starting point for your build.  Sounds like you've been wading into the math way deeper than I've looked into.

I'll try to get over to the mill later and get that thread info for you.  Suspecting 18mm or so and probably a standard pitch.

Not a whole lot of free space under the spring once tensioned, but it works well, more like .05" instead of .5"
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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Re: dynamic or static tension
« Reply #25 on: August 05, 2019, 05:53:26 PM »
Still sprinkling a little, but the sun is out.

The threads to tension the blade on this mill are 3/4-10  surprised me since everything else is metric.  Hope this helps you out.



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Re: dynamic or static tension
« Reply #26 on: August 05, 2019, 06:56:05 PM »
Dont know that much about the physics of what has been discussed here.
I crank my WM LT40 till the needle is nearly vertical and saw.
I'm thinking that the V belts on the wheels must take care  of any instant increase in tension due to  a chip or piece of bark engaging the wheels.
Works for me.
I guess the Cooks steel wheels are spring loaded to accomplish the same thing, Is this an accurate assumption?
LT40SHDD51
Kubota 8540 tractor, Farmi winch
Kubota 900 RTV
Polaris 550 Sportsman ATV
1 Husky 1 gas Echo 1 cordless Echo vintage Homelite super xl12
241 acres of woodland

Offline charles mann

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Re: dynamic or static tension
« Reply #27 on: August 05, 2019, 10:53:15 PM »
@MAF143 
thanks, ill take a look see on their site. 
Temple, Tx
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Offline Pabene

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Re: dynamic or static tension
« Reply #28 on: August 06, 2019, 04:24:30 AM »
Petefrombearswamp, You describs the function very good. I have steel wheel in my mill and would like to add a springpackage, unfortunatly it is complicated to do in my mill. I protects my mill by a skraper as acts as a guard against sawdust and bark between blade and wheel.
The reason for me to suggest a longer spring package is that it would give a more linear tension force during the movement from a heated blade or instant pinched bark. That way the blade will survive better. I like bellewille washers as it is a lowcost solution, if you would end up in a too low force you can just rearange the package of washers insted to buy a new expensive toolmaker spring. 
I have experiance from Pilous saw mills with Bellewille washers in the tension system. I have checked the tension on a lot of Pilous mills with my tension meter. The tension are equal, within few percent, from mill to mill. Insted of a torque wrench they use the length of the compressed package as is the reference. It will give you a higher accuracy as the variation in friction in the threads is bypassed.
Woodmizers spring solution with a airfilled rubber ball looks also good, I think it meets all you need.

Offline John Bartley

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Re: dynamic or static tension
« Reply #29 on: August 06, 2019, 07:57:47 AM »
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.


A hydraulic ram is what tensions my Champion mill.  The ram has a pressure gauge on it, and as long as I keep the pressure close to my optimum number, all works well and has been for eleven years with no shrapnel or other bad things happening.

When I got my mill I learned about band tension, strain vs psi etc.  I then clamped a vernier across the band and tensioned to see what pressure got me the correct strain.  That's the psi that I run ....
cheers
Kioti DK35HSE w/loader & forks
Champion 25hp band mill, 20' bed
Stihl MS361
Stihl 026

Offline JoshNZ

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Re: dynamic or static tension
« Reply #30 on: August 10, 2019, 07:08:17 PM »
Probably better to go in this thread than my build sorry Charles XD

I only skimmed it sorry if it's been said but how does one go about tapping the cylinder of a jack? I did pull the top off one at home here, the outter wall is not the cylinder wall it is the reservoir and the cylinder is nested inside that. So you would have to drill the wall, and cylinder, tap the cylinder, screw in the output nipple then weld or seal the nipple to the outter wall somehow?

Has Arnold been around here lately I wonder how he did his? Am I on the right track?

Also.. could you force the cylinder to hold a wee pocket of air as a spring/dampening system or are they designed to bleed this out when you let up?

Offline charles mann

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Re: dynamic or static tension
« Reply #31 on: August 10, 2019, 07:35:56 PM »
@JoshNZ 
I think the drilling of the cylinder was explained in a sub link to a link provided, i think maybe on page 1. Ill look when i get off tonight. Iv got 5 web browsers open, with 3-6 pages per window. You might find it faster in you go the provided link and read through it till another link is posted. Its either in the sec link or another link provided within the sec link. Just gotta read through the stuff like did and stumble across the info. 
Temple, Tx
Fire Fighting and Heavy Lift Helicopter Mech
Helicopter and Fixed Wing Pilot

Offline charles mann

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Re: dynamic or static tension
« Reply #32 on: August 11, 2019, 01:57:13 PM »
@JoshNZ here are the links i read through. 

Wm spring blade tensioner conversion in Sawmills and Milling

Tensioning method for homemade bandsaw mill in Sawmills and Milling

Hydraulic Tensioner in Sawmills and Milling

after sign through these, plus what others left on my thread, i found the info i was looking for. now i just have build it in a way that will work on my set up.
Temple, Tx
Fire Fighting and Heavy Lift Helicopter Mech
Helicopter and Fixed Wing Pilot

Offline JoshNZ

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Re: dynamic or static tension
« Reply #33 on: August 11, 2019, 05:34:53 PM »
Are you referring to the post with the gauge tapped in the top of the cylinder? The cylinder is not full of oil in the jack I have here, the seal is at the bottom of it and the top has a threaded 'foot' as a means of taking up slack before you get the jack working which is great if it's used as a jack!

Offline charles mann

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Re: dynamic or static tension
« Reply #34 on: August 11, 2019, 06:30:39 PM »
Are you referring to the post with the gauge tapped in the top of the cylinder? The cylinder is not full of oil in the jack I have here, the seal is at the bottom of it and the top has a threaded 'foot' as a means of taking up slack before you get the jack working which is great if it's used as a jack!
IDK, i didnt go into depth about the gauge on the jack bc im not going that route. I simply provided additional links that might yield info for you. I did see a gauge on a jack, dont remember which link it was and wasnt going to read through them to find out bc i didnt have the time and i wasnt going that route.
Im sure there is something within those links or links within those links that might be beneficial for your purpose.  
Temple, Tx
Fire Fighting and Heavy Lift Helicopter Mech
Helicopter and Fixed Wing Pilot


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