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blade tension springs

Started by jbuck984, September 06, 2010, 12:21:15 AM

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jbuck984

Hello everyone!! I'm a newie here and with just an hour of thread searching under my belt I have learned a lot! Thanks!! I have a homemade mill with a hydraulic ram type blade tensioning unit. I want to add springs to the unit so I don't have to worry anymore about stopping and retensioning. My question is about the springs, what size should I be looking for? I know I have some valve springs with around 300# per inch and that doesn't seem like it would be enouph. What are you guys using?

5quarter

Jbuck,

   I don't have an answer to your question, but let me be the first to say welcome aboard. Someone will be along soon to help you out ;)
What is this leisure time of which you speak?
Blue Harbor Refinishing

ladylake

My TK uses a spring for tension, I'd guess it's about 5 times stronger than a valve spring. Do you use a check vavle for no leak down with hyd tensioning?  Steve
Timberking B20  18000  hours +  Case75xt grapple + forks+8" snow bucket + dirt bucket   770 Oliver   Lots(too many) of chainsaws, Like the Echo saws and the Stihl and Husky     W5  Case loader   1  trailers  Wright sharpener     Suffolk  setter Volvo MCT125c skid loader

bandmiller2

Welcome Buck,easiest foolproof way is to order a spring from one of the co.'s that sell bandmills.It requires a rather heavy spring auto valve springs won't cut it.If you can measure the spring on a factory bandmill then go to a farm equip. dealership look around they have big springs on implements.Myself I used the biggest spring I had and put anouther inside.I hesitate to give dimentions as springs vary so much but you want a stiff one. Frank C.
A man armed with common sense is packing a big piece

weisyboy

would a spring of a heavy duty chisel plow work?
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Magicman

Welcome jbuck.  Yes, there is loads of information here.  Welcome a"board".    :)
Knothole Sawmill, LLC     '98 Wood-Mizer LT40SuperHydraulic   WM Million BF Club Member   WM Pro Sawyer Network

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paul case

welcome jbuck,
ditto on franks comments. ez boardwalk uses springs totension with. give edward a call since he is a forum sponsor his contact info is in the column on the left f the page.   pc
life is too short to be too serious. (some idiot)
2013 LT40SHE25 and Riehl edger,  WM 94 LT40 hd E15. Cut my sawing ''teeth'' on an EZ Boardwalk
sawing oak.hickory,ERC,walnut and almost anything else that shows up.
Don't get phylosophical with me. you will loose me for sure.
pc

Chuck White

Welcome to the Forestry Forum JBuck!

There is a wealth of information within these pages.
~Chuck~  Cooks Cat Claw sharpener and single tooth setter.  2018 Chevy Silverado and 2021 Subaru Ascent.
With basic mechanical skills and the ability to read you can maintain a Woodmizer  LT40!

jbuck984

I love this website already! Was up way to late looking to the threads! I did some looking around and found that cooks tensioner gets 1600-1700# of tension through a 850# spring on a fulcrum. So yeah thats like 5 valve springs. I travel by 3 farm implements daily so I'll swing into one of those places and see what they have.

John Mc

I know nothing about band saws, but do know a bit about springs. If you are looking for something heavier tan a valve spring, you might look in to Die Springs. They are made in a wide range of sizes, some of which are quite stout.

Here's a link from McMaster-Carr:
    http://www.mcmaster.com/#compression-and-die-springs/=8qe80f
if you scroll down the page a big, you can select springs by load range or by rate (#/inch) range.

John Mc
If the only tool you have is a hammer, you tend to see every problem as a nail.   - Abraham Maslow

Bill Gaiche

jbuck984, welcome aboard. I built my own bandsaw mill. I bought W/M urathane material spring for the LT15. Compress it under load 3/16" by using a screw adjuster or do what I did and build a tensioner very similar to the LT15. It works great for me. bg

LorenB

jbuck984,

A couple of years ago I did some tension calculations for a company that sells blades.  I wanted to know what tension I had on a blade at a given pressure on the hydraulic accumulator that is the tension system on my Baker sawmill. 

A common 1-1/4" x 0.042" blade has a cross sectional area (through the gullet) of about 0.05670 sq. in. 

The desired tension on that blade is about 32,000 to 38,000 psi.  This works out to a force of 1814 to 2154 pounds on the band.  Since your wheels are tensioning two bands (top and bottom), you will need to create a pull of 3628 to 4308 pounds. 

Size your springs accordingly. 

Good luck.
– Loren
Loren
Baker 3667D portable sawmill, Cook's edger, Logrite arches & peaveys.  Husky 272XP chainsaw & two Echos.

jbuck984

Thanks for all the help and welcomes! I ordered a die spring that has 1600-1900 working load. I hope that will be acceptable. Now I wish I would have ordered a bigger one or two to see which gives the best results. When I modify this tensioner I think I will keep in mind and leave room for some testing of other springs to see which gives the best results.

jbuck984

Just for an update, I got the springs in the saw today. My results may be a bit inconclusive since I bought the die springs off ebay and I may not have the correct specs for them. I used 2 2"x4" green raymond die springs and 1 2"x5"blue raymond die spring sitting side by side with the blue preloaded 1". I tensioned the blade to .004" using a caliper and the springs are maxed out, well the greens are since 1" of travel is all they are rated for. At 1" of travel that should be around 4600 maybe more pounds tension on the band. Loren, I'd say your calculations are on the $$$. I figure there may be some friction loss or something like that going on. As far as I'm concerned its good to go but I will get another stiffer green spring ordered and swap out the lighter blue one so the springs aren't so close to max. Now hopefully I will get a chance to cut tomorrow and I'm really looking forward to not having to stop and retension anymore!! Thanks guys!!

bandmiller2

Buck,the best band tension is just enough,less tension will give you longer band life.Look up Suffolk [timberwolf] bands they describe the flutter test to find the proper tension,basically run without the guides keep lowering tension until the band starts to flutter then increase the tension some and try cutting.Many try to mask the problem of dull teeth and poor set with too much tension.Your in the ballpark experiment with a little less. Frank C.
A man armed with common sense is packing a big piece

LorenB

Frank,

I used to believe that less band tension would result in longer blade life because that seems intuitively obvious.  I have found that for my saw, that's not the case. 

The Baker 3667D has what I consider the best band tensioning system made.  It uses a hydraulic accumulator to maintain pressure on a cylinder that forces the bandwheel out.  The pressure on the accumulator converts directly to a tension on the blade.  If you know the pressure, the cylinder diameter, and the cross-sectional area of your blade, you can calculate the tension on the band. 

Suffolk (Timberwolf) recommends a tension of 28,000 psi, and that's what I ran for a couple hundred hours.  I broke way more blades than I thought I should. 

Eventually I figured that I had nothing to lose by increasing the tension, since my blades weren't lasting long anyway.  I found that if I tensioned the blade to 31,000 psi, or even up to 34,000 psi, the blades lasted much longer.  I still occasionally have a blade break, but it's probably 10-25% of what it used to be. 

I am unable to explain why this is so, but my guess is that it has something to do with flutter or waviness as the band cuts.  Even though I don't understand why, I do know that higher tension is working for me to prevent band breakage. 

– Loren
Loren
Baker 3667D portable sawmill, Cook's edger, Logrite arches & peaveys.  Husky 272XP chainsaw & two Echos.

ladylake

 If your losing tension with hydraulic tensioning your still going to lose tension with springs , you would need a good check valve to keep the same tension.   Steve
Timberking B20  18000  hours +  Case75xt grapple + forks+8" snow bucket + dirt bucket   770 Oliver   Lots(too many) of chainsaws, Like the Echo saws and the Stihl and Husky     W5  Case loader   1  trailers  Wright sharpener     Suffolk  setter Volvo MCT125c skid loader

bandmiller2

Loren,your experiance with tension is interesting I've run two bandmills an lt-70 and my home built.The woodmizer lt-70 I would get 5 or 6 sharpenings before breakage.My homebuilt with light tension I've never broken a band they just get sharpened down to where they don't cut well.Their may be outher factors at play here.Frank C.
A man armed with common sense is packing a big piece

LorenB

Quote from: ladylake on September 15, 2010, 07:17:50 PM
If your losing tension with hydraulic tensioning your still going to lose tension with springs , you would need a good check valve to keep the same tension.   Steve

Steve,

I never said I was losing tension.  I said that my blades last longer if I increase the tension.  It stays at whatever value I set. 

– Loren
Loren
Baker 3667D portable sawmill, Cook's edger, Logrite arches & peaveys.  Husky 272XP chainsaw & two Echos.

LorenB

Quote from: bandmiller2 on September 15, 2010, 08:46:26 PM
Loren,your experiance with tension is interesting I've run two bandmills an lt-70 and my home built.The woodmizer lt-70 I would get 5 or 6 sharpenings before breakage.My homebuilt with light tension I've never broken a band they just get sharpened down to where they don't cut well.Their may be outher factors at play here.Frank C.

Frank,

I'm sure there are other factors at play.  I wish I knew what they are. 

It only makes sense that bands would last longer if they are under less stress as they are used.  On my saw, there are obviously factors other than just tension that affect blade life. 

– Loren
Loren
Baker 3667D portable sawmill, Cook's edger, Logrite arches & peaveys.  Husky 272XP chainsaw & two Echos.

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