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Author Topic: Bandmill Blades Breaking  (Read 36741 times)

Offline HaroldCR - AKA Fla.-Deadheader

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Re: Bandmill Blades Breaking
« Reply #50 on: February 25, 2016, 06:22:39 AM »

 Thanks for the response. Are you running the same tension as you were previously ?

Offline backwoods sawyer

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Re: Bandmill Blades Breaking
« Reply #51 on: February 25, 2016, 10:48:29 PM »
i tried a lower tension but went back to where I was

Offline backwoods sawyer

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Re: Bandmill Blades Breaking
« Reply #52 on: March 08, 2016, 11:33:33 PM »
First three saws out of the box made it to the sharpening room but 4-5 and 6 all broke, #7 found the hook end of a lag bolt twice.

Offline HaroldCR - AKA Fla.-Deadheader

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Re: Bandmill Blades Breaking
« Reply #53 on: March 09, 2016, 07:06:09 AM »

 That's not very encouraging. With the amount of blades that are breaking, it sure seems that something is amiss with the tuning of the mill, perhaps ??  Don't have any ideas to help. I still believe excess tension is involved.

 I have a photo of a very large, ugly Live Oak, which is one of the densest woods ( Cannon balls would not break or penetrate the hull) and we cut it up no different than any other hardwoods we encountered .

 This may be tough to figure out.

Offline kelLOGg

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Re: Bandmill Blades Breaking
« Reply #54 on: December 20, 2020, 08:26:36 AM »
I'm very late to the party and I hope this adds something helpful to this old discussion.

When suppliers of bands provide the stress (lbs/sqin) to be applied to their bands, those of us (who have spring tensioners and no gauge to tell us when we have reached this recommended tension) need more information. Proper stress can be obtained by measuring the stretch (strain, in engineering language) when tension is applied to the band and plugging it into the equation below.
 
Stress(or tension in lbs/sqin) = E(modulus of elasticity in lbs/sqin)  X Strain (dimensionless quantity)
where E=30,000,000 lbs/sqin  for tool steel.

Strain can be measured by opening calipers to a specified length and clamping to the band with small c-clamps and tensioning the band. How much tension depends on the band thickness and width. I run Kasco 4 degree, 1.25, 0.045 thick bands so I contacted Cutting Edge and was told 20,000 lbs/sqin was a recommended value.

Strain=20,000/30,000,000 or 0.000667 is the strain value.

Strain is defined as the change in length of the band as it is stretched divided by its original length, so if I open the caliper to, say, 5.5 inches, the right amount of stretch in the band is 5.5 X 0.000667 or 0.0037 in. So I tension the band until the caliper reads 5.5 +0.0037 or 5.5037 and I should have 20,000 psi on my band. This should remove the guess work in tensioning a band and give better band life.

I have just learned all this information so I have high hopes that my band life will increase as well as yours.
 
Apparently, of equal importance as band tension is that the band back does not contact the flange on the roller guide except during extreme sawing conditions. I had to push my roller guides back a bit as Tom the Sawyer does.
« Last Edit: December 21, 2020, 04:16:15 AM by kelLOGg »