Breaking Blades

[dhp3228]

I'm working on a Log Master mill from the mid 90's and it continues to break blades. It was recently taken to the manufacturer and they realigned it and gave it a green light. We got it back ran 2 blades through so e lumber and resharpened them. We cut a couple hundred board feet with the first and it broke then the second had the same problem. We then put a third brand new blade and with in a couple hundred board feet it broke.

We used to run the tension at 3500 and it was breaking blades that's when we took the mill to get worked on. Now we run it at 6000. The first blade with one sharpening broke at 4000, the second blade with one resharpen get broke at 6000, the third new blade broke at 6000.

We checked the blade guide rollers with a gauge and it's not off but a few thousands.


What are yalls thoughts?

[Den-Den]

You might check the wheels for out of round condition aka radial run-out, that would be my first guess.  Next, try to determine actual stress that you tension the blades to; I am assuming that the numbers you quoted are hydraulic pressure that extends a cylinder which puts tension on the blade.  That cylinder's diameter, the blade width and thickness are important parts of the equation.

[ladylake]

( We checked the blade guide rollers with a gauge and it's not off but a few thousands) From what?   Did this mill always break blades or just start top break them.  A few years back I got a bad batch of blades, every one broke after the first sharpening.  Steve

[ncsawyer]

Does the break occur at the weld or elsewhere?

[POSTON WIDEHEAD]

Does the break occur at the weld or elsewhere?

Are your blades turning on metal or belts?

[dhp3228]

It has always been breaking blades from my understanding. Previously it was 2" blades that the current owner then had the wheels machined down to accept smaller blades by the manufacturer.

[dhp3228]

Of the 3 blades that I've witnessed none have been at the weld. All have extensive cracking in the gullet areas not sure if that develops in the flying off the wheels when the break happens but either way the cracks are there. They aren't there when we first put them on.

[dhp3228]

Does the break occur at the weld or elsewhere?

Are your blades turning on metal or belts?

Metal wheels

[dgdrls]

Of the 3 blades that I've witnessed none have been at the weld. All have extensive cracking in the gullet areas not sure if that develops in the flying off the wheels when the break happens but either way the cracks are there. They aren't there when we first put them on.

Gas, diesel, electric rig?

What width bands are you running now and did the Manufacturer adjust the S.F.P.M. speed when they
turned the wheels to run the narrower bands?
Recheck the wheel bearings, as @Den-Den indicated radial-run out, may be working against you.

any chance your sawing, feeding the logs too fast??

Dan

[dhp3228]

Of the 3 blades that I've witnessed none have been at the weld. All have extensive cracking in the gullet areas not sure if that develops in the flying off the wheels when the break happens but either way the cracks are there. They aren't there when we first put them on.

Gas, diesel, electric rig?

What width bands are you running now and did the Manufacturer adjust the S.F.P.M. speed when they
turned the wheels to run the narrower bands?
Recheck the wheel bearings, as @Den-Den indicated radial-run out, may be working against you.

any chance your sawing, feeding the logs too fast??

Dan

Diesel rig
1.5" bands

It was breaking 2" bands before then we took the mill and they turned the wheels to use 1.5" bands.

I would think the run out would have been worked out just a few weeks ago since it hasn't been out of the shop that long.

[ladylake]

 Are the band wheels flat or crowned, I've heard flat are hard on bands.  How far behind the blade is the flange, how much down pressure, does the blade track the same when you turn it backwards, does the mill have a good chip deflector to keep debris from getting between the blade and wheels.  Seems like your going to have to fix it yourself as the shop didn't,  good to know how anyway. Steve

[dhp3228]

Are the band wheels flat or crowned, I've heard flat are hard on bands.  How far behind the blade is the flange, how much down pressure, does the blade track the same when you turn it backwards, does the mill have a good chip deflector to keep debris from getting between the blade and wheels.  Seems like your going to have to fix it yourself as the shop didn't,  good to know how anyway. Steve

Band wheels feel flat and are believed to be so as they just got out of the shop from getting milled down to not be running 2" bands any longer.

Down pressure look to be less than 1/2"

It tracks the same backwards and forwards

No chip deflector

The band is flush with the back of the wheel this leaving about 3/16" from edge of band wheel to gullet on band

I agree we will have to fix it as it has been an ongoing issue that's not been remedied yet. Just going to be frustrating.

[ladylake]

 
If your band wheels are flat I'd get them crowned like Cooks wheels.  The flange on the guide wheels needs to be 1/4" behind the blade as Cooks recommends and if too close you will break blades fast, 1/16 or 1/8 back might work on a 10hp mill running 10° blades but high hp mills running low hook angle will push the blade back more causing it to bend around the flange if its too close.  Steve

[dhp3228]

If your band wheels are flat I'd get them crowned like Cooks wheels.  The flange on the guide wheels needs to be 1/4" behind the blade as Cooks recommends and if too close you will break blades fast, 1/16 or 1/8 back might work on a 10hp mill running 10° blades but high hp mills running low hook angle will push the blade back more causing it to bend around the flange if its too close.  Steve

The blade guides dollars are about 1/4" behind the blades.

As to the frowning I'll mention it but since Log Master decided to go a different route I'm sure it'll be a hard sale.

On a different note the guy I'm helping did say this past weekend that he had adjusting the height on the blade guide dollars after feeling like they where putting to much downward deflection in the blade.

But.... That didn't help we notice a crack in a brand new blade forming after we made that adjustment.

He made a phone call and the manufacturer said to make sure the blade guide backs where parallel which they weren't and we made that adjustment at quoting time so it'll be a day or 2 till we find out the results of that action.

Please don't hesitate to continue giving advice. I'll keep y'all posted and thanks for the wisdom that's been given so far.