Band Tension Dropping

[DR Buck]

Now that I've a got a  few thousand bf under my belt, ( I think around 15 K   ) I've noticed that my bands start to lose tension about the time they need to be changed out.  

Questions are.....Is this normal on all band mills?  What's causing this?  Is it because of increased friction due to blade starting to dull?   Should I change out the blade when it starts or wait for the beginning of the wavy cuts?   ??? ??? ???

[MrMoo]

Buck,
I haven't run across this. Usually when I first put a blade on the machine (new or used) the tension drops for the first couple of cuts & then it settles out with no change after that.

[LeeB]

my experiance has been that you can tighten it up and get a few more cuts but it is better to just change the blade. I agree that as the blade gets duller it starts to get hot and stretches somewhat, thereby loosing some tension. Some of the time when I tighten up I end up with a broke blade. LeeB

[newguy]

Sounds like LeeB hit the nail on the head.  Not speaking from sawing experience but from experience with metal.  Carbon steel expands .00000633 units per 1 degree F.  Doesn't sound like much but if you have a 13' 8" band and the temperature of it is running 100 degrees above normal the band will grow by .103" almost 1/8"

[Tom]

On the hydraulic band tensioners there is not the 'reserve" pressure found on spring tensioners.  When the band stretches due to heat, it loosens.  Heated bands can be normal work heat or severe heating caused by dulling, misalignment or slippage on the band wheels.

Even ambient temperatures can effect the tension.  On a hot day, the sun going behind a cloud can cool the oil enough to cause the band to loosen.  When the sun comes back out, it heats the oil and the band will tighten.  It is more noticeable as the sun climbs in the sky, so you may only notice it as the hydraulic pump is uncovered from the mills own shadow.

Loosening bands could be caused by a heated pump, stretched band or even cracks in the blade. An erratic, vibration appearing, movement of the pressure gauge is usually caused by sawdust or a wood chip caught under the band tire or a build-up on the tire.

[MemphisLogger]

Just today I went from sawing dry, spalted Pecan to fresh felled Pecan and my blade tension jumped WAY up.

I always run just a trickle of water to keep the blade temp constant and I believe this helps with minimizing gullet cracks.

  

[DR Buck]

My LT40HD25 also has the lubmizer option.   I usually have it operating in a pulse mode adding a water spray every 10 seconds or so.  When I start to feel vibration or the noise level goes up I switch to constant water flow until it quiets down.  Normally this is about 15 -20 seconds when not in the log.

However, all that said, when the blade loses tension and I adjust it back up, it will continue to lose tension and I keep adjusting it up and it keeps losing tension.  VERY soon after that I start getting wavy cuts.