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blade tension

Started by timberfaller390, February 23, 2015, 04:29:12 PM

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timberfaller390

For those who are running homemade mills, how do you gauge your blade tension? Also what type of tensioner are you using. Mine has a floor jack cylinder and a bolt that pushes one band wheel out. I always end up using the bolt to put the last bit of tension on because the jack just doesn't get it tight enough.
L.M. Reese Co. Land Management Contractors
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Den-Den

Mine has a hydraulic cylinder and a manual pump to tension the blade.  I use a hydraulic pressure gauge to get the tension and then lock in the setting with a threaded rod before releasing the hydraulic pressure.
You may think that you can or may think you can't; either way, you are right.

prittgers

You can buy a very accurate tension guage.  It clips on the blade and measures the 'stretch'.  Readout is in # directly.
Parker Rittgers
Professional Sawyer, Retired, well, not really !
WoodMizer Alaska | 907.360.2497 cell 336.5143 office BevelSider.com ? Everything BevelSider
907.336.5143
prittgers@aksamill.com

drobertson

that gauge prittgers suggested is a pretty good idea, and after thinking on this a spell today, I have to wonder how the shafts and bearing are designed, it seems that this would play an important role in the scheme of things in regards to the amount of pressure applied to these components.  just a thought, and another thought, may be off track, but if you had  1-1/2 ton bottle jack that be around the right tension if the shafts and bearings could maintain.
only have a few chain saws I'm not suppose to use, but will at times, one dog Dolly, pretty good dog, just not sure what for yet,  working on getting the gardening back in order, and kinda thinking on maybe a small bbq bizz,  thinking about it,

timberfaller390

Prittgers, that sounds like what I need. Is there a brand name? Or what exactly do I look  for?
Drobertson, most bottle jacks don't work reliably when on their side.
L.M. Reese Co. Land Management Contractors
Stihl MS390
John Deere 50G excavator
John Deere 5103
John Deere 440 ICD dozer

valley ranch

Timberfaller, Wouldn't mind having a look at your tensioner. Did you build the mill?

Tension gauge sounds like a good idea.


Richard

bandmiller2

I have a heavy spring with a handwheel and screw to tighten, just bring it up almost tight coils. A lot of tension on a band is just a crutch to cover up other problems. High tension greatly reduces the life of a band. You can't always believe manufactures they want their mill to cut straight and you to buy more bands. A properly set and sharp band only needs light to moderate tension to cut well. Frank C.
A man armed with common sense is packing a big piece

MartyParsons

Hello,
Some other things to think about. A thin blade will streach different than a thick blade. So it will take less pressure to strain a .035 than a .055. I like to tighten the blade to the upper limits.
Wood Mizer sells a band tension gauge, I also think there are other companies that sell this tool.
If the tracking changes when you change the band tension then it is a good chance something is bending!
Some band blade manufactures have different specs for band tension.
Wood Mizer bands work best tight or strained. My opinion.
Hope this helps.
Marty
"A pessimist sees difficulty in every opportunity; an optimist sees opportunity in every difficulty." -Winston Churchill

valley ranch

http://www.suffolkmachinery.com/six-rules-of-sawing.html


How close it this to the correct way of tensioning a blade?

Richard

scrout

My Linn has a 1 inch diameter hydraulic tensioner.  Suggested set point is 2300 psi for a 1.25 inch wide blade.
So 1 inch diameter is 0.79 sq inches, so about 1817 lbs of force.
You can also just attach a decent micrometer/caliper directly to the blade to measure the stretch.
I forget the formula, but something like a one thou stretch over 10 thou is so many lbs of force.
Found it:
https://forestryforum.com/board/index.php/topic,7923.0.html

Money shots:
Lennox replied to my question and said 0.0025" on 5" test. (blade?)
============
I'm running 0.042" x 1 1/2" bands, but the strain should remain the same no matter what thickness or width.
Mounting the caliper, Don't try to get exactly 6.000", way too difficult, just get it close and then add 0.005" to it.
====
I gave Simonds a quick call and they said their Red Streaks should be stressed 25,000 to 30,000 psi.
Thus:
Stress = E * Strain
25,000 psi = (29,000,000 psi) * Strain
Strain = 0.00086 in/in
Having a distance of 6" gives 6" * 0.00086" = 0.005" deflection.
So, clamp the caliper, opened to 6.000", on your band with zero tension.  Then tension your band until it reads 6.005".  This will give 25,000 psi in the band.
For 30,000 psi your caliper should read 6.006"

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