Blade strain in lbs

ozarkgem · April 24, 2016, 09:01:43 PM

I know some mills have blade strain gauges that are hydraulic but the strain would depend on the diameter of the cylinder. So my question is how much strain in lbs is there on a 1 1/4 blade to make it cut right. I am thinking of putting gas springs on my mill and have no idea how much strain to put on the blade. I just have a heavy die spring on it now. The gas springs do not vary in resistance when depressed. The strain is the same throughout the travel. Good for 5 million cycles. That is a lot of blade changes.

Den-Den · April 24, 2016, 09:21:25 PM

Different manufacturers may have specific numbers but capability to put 15,000 - 25,000 psi tension on the blade should enable you to find what works for your mill. Measure the width of the blade at the gullet and multiply that by the thickness to get the cross-section area of your blade.

lbs force = width X thickness X 25000
example: width @ gullet - 1.08", thickness - 0.045" 1.08 x 0.045 x 25000 = 1215 lbs
note that your gas spring will need to apply twice that much since the blade is pulling with 2 sections.

ozarkgem · April 25, 2016, 05:13:31 AM

I see . Thank you

drobertson · April 25, 2016, 08:06:50 AM

it also seems like the gas would or could compress,, but I have never seen them so just a guess,

dgdrls · April 25, 2016, 09:26:05 AM

As Den-Den noted I would suspect the value would change a bit depending on the blade manufacturer,
even from blade to blade although this factor may not change enough to be a concern
compared to manufacturer.

Less tension means longer blade and component life.
Suffolk machine has a very good read on bandmill blades.

Dan

Percy · April 25, 2016, 09:32:28 AM

Taken from Cutting Edge's post from last year some time.......

Get an inexpensive HF torque wrench and a 6" caliper. Open the calipers to 6", clamp it onto a slack blade and tighten the blade until it reads you have stretched the blade about 0.005". This will give you approx. 20,000 lbs. of strain on the blade. use torque wrench setting for blade changes.

ozarkgem · April 25, 2016, 07:20:26 PM

Quote from: drobertson on April 25, 2016, 08:06:50 AM
it also seems like the gas would or could compress,, but I have never seen them so just a guess,

They do compress. They act just like a spring, the guy I got them from said the spring rate stays the same all through the stroke. I picked up a couple today. I will let you know how they work. Will these mill mods ever end.

DDW_OR · April 26, 2016, 12:54:38 PM

my TK-2000 is between 1,500# and 2,000#
Timberking blades.

scrout · April 26, 2016, 01:10:48 PM

My Linn Lumber mill has a 1 inch bore hydraulic cylinder and says 2300 psi for 1.25 inch blades.

ozarkgem · April 26, 2016, 05:40:53 PM

Quote from: scrout on April 26, 2016, 01:10:48 PM
My Linn Lumber mill has a 1 inch bore hydraulic cylinder and says 2300 psi for 1.25 inch blades.

If my math is correct that would be .785 area X 2300 gives you about 1800 lbs of strain.
Then again I used online calculators so who knows. Sounds about right though

ozarkgem · April 26, 2016, 05:43:38 PM

Quote from: dgdrls on April 25, 2016, 09:26:05 AM
As Den-Den noted I would suspect the value would change a bit depending on the blade manufacturer,
even from blade to blade although this factor may not change enough to be a concern
compared to manufacturer.

Less tension means longer blade and component life.
Suffolk machine has a very good read on bandmill blades.

Dan

I am sure less tension would give longer blade life but poorer quality lumber. I will go for less life and better lumber.