Boom! Broke another blade

[Henry-Adams]

Hi all, sorry it's been quite a while since my last post, so I'll try to bring you up to speed. I discovered this fine site about a year ago after I had just bought a new LT40 hydraulic. The business started out really slow and I thought that I might have bought an expensive play toy. Well you all warned me to enjoy the quiet while it lasted. You all were right, business has picked up to the point that I might just be able to give up my day job in the spring. Anyway I just wanted to thank each one of you for your wonderful advice. I may not have been posting much but I sure have learned to read what you all have to say.

I've run into a bit of a problem. The other day I was cutting red pine and red oak for a customer of mine when I started to have blade problems. I was using blades that had just come back from their first time being re-sharpened. The first blade I ran cut like a dream. I changed out blades after the first one dulled and started in again. I was cutting through an 18" red pine with my lubemizer set at fast intermittent when I noticed that every time the spray would hit the blade there would be a puff of steam. Just as I was starting to ask myself "what the heck?" BOOM broken blade.  I never heard the engine start to bog just boom. I just chalked it up to stuff happens. Changed out blades and finished the cut. As I started back into the same log for the next cut the blade dove like crazy at the start of the log but straightened out for the remainder of the cut. The tension was set OK and I entered the log slowly as I always do. Scratching my head I decided to just do a shallow clean up cut to remove the wavy surface when the blade did the same thing in the same place. It was a clear section of the log near the butt end and there were no knots close to where I was cutting. I couldn't get the blade to cut straight so I changed it out again and the next one cut through the log just fine. Weird. Ok then we started to cut red oak using the same blade. I was cutting 1x12's when all of a sudden BOOM another blade broke. The day and my mood were starting to turn to the dark side at this point. I had never broken a blade and now I just detonated 2 in the same day. I changed out blades again but the saw seemed to work harder than usual and I was chasing the blade tension all over the place until I turned on the lubemizer to continuous spray. At that point the blade settled down and cut just fine. I don't normally run the lubemizer in hardwoods only in logs with heavy pitch.

Anyway the day ended with a happy customer. When I got the mill home I noticed that one of the broken blades had what looked like black pitch on it. After looking closer I found that the "pitch" was in fact rubber from the drive belts. The blade was riding well clear of the drive wheels and without looking close you would think the belts were fine but on close inspection I noticed that the surface of the belts had started to melt. More head scratching.

I'm off to pick up a couple of new belts this morning and we'll see if that changes anything. Have any of you got any ideas why in the world I'm starting to generate so much heat?

Signed dazed and confused  ???

[Jeff]

Well, since I am very new at this myself, my ideas are pretty much guesses based on my limited sawing experience, but I do saw both oak and redpine.  My guess is that you were using the same set blades for the pine as with the oak. Probably somewhere 14 to 18 thousanths? If so, I think that the blades were heating up from friction as you need more set and more lube for sawing red pine. They got so hot. The heat caused the blades to fail and also caused the fluctuations in tension.

I dont have a lube-mizer but I pay close attention to the "sound" my blades make as they run, and usually I can tell weather they need more lube or not. Sawing oak, I use very little. Sawing Pine, I run the water stream pretty steady, not a lot, but just steady.

Now, someone that really knows what they are talking about can come and really help out. I just wanted to put my guess in here. :D

[Norm]

Well until that peson shows up I'll throw out my guesses. :D Look at your blade guides to see if you have them adjusted right. Sounds like your getting some friction causing the blade to heat up and fail prematurely. Check to see that they freewheel easily, I put one pump of grease once a week if I'm doing much sawing. Good luck.

[Rockn H]

There are a few questions that come to mind that may help, such as.  What thickness are your blades?  What kind of blades are they?  Who resharpened them? 

A thicker blade such as a .55 will develope stress cracks a break much quicker than a thinner blade.  The blade that would dive sounded like a few teeth were out of set, but you said it would level out.  This causes me to think it was dull.  I've started to take that as a clue my blades are dull and need to be changed.  Within the first 15 inches of board there will be a  shallow arch about a 1/2 deep for maybe 6".   On the blades that broke, look to see if there are any cracks running the width of the blade.  They will start at the bottom of the gullett.  If the cracks are there my guess is and it's just a guess, the blades were dull and were being pushed through the log.  If the blades were resharpened, look at the gullett on one or two that you haven't used yet.  See if the entire gullett has a fresh grinding showing.
Again, wait a little while and somebody that really knows will be by. ;)

[Tom]

I'll never say I know. :D   Every time I do, it's something else. ;D

If the bands are breaking almost immediately, then I would suspect that there are already cracks in the band or that the gullet might not be ground with a smooth curve or the weld broke.

Sometimes I have blades fail after a sharpening and the fault is not the sharpening but that I pushed it too hard and too long during its first use.   That's were the stress cracks develop and the luck would have it that the band gave up upon being remounted again.

It pays to check guide alignment and stuff like that just as a place to start, regardless as to whether alignment is at fault or not.

Heated bands and melted rubber sounds like either wheels being moved out of co-planer (sometimes someone grabs the wheel adjustment handle instead of the blade tightening handle and throws the saw out of whack) or that the blade isn't being tensioned enough and is slipping on the V-belt.

I would suspect that the teeth have lost their set and are not sharp, given the symptom of diving blade.  It could even be that the hook was changed drastically.  This can happen during sharpening unbeknown to the sharpener operator by dirt interfering with the clamp of the device.

Sometimes an operator will try to sharpen too fast and produce a dull point as well.

It could also happen if the blade hit something on the mill.  It might have touched a part of the shroud or the door or the guide or run too far back on the band wheel and had the set removed or the tips destroyed.

If you are running OK with other blades, it pretty much pin points the sharpened blades as the problem.   Close examination may reveal stress cracks.  A conversation with the person doing the sharpening might help to discover the cause.

If you are going to use someone else to sharpen your blades, it pays to have them done by a reputable outfit that has a lot of experience and good equipment, not just a yeahoo down the road who just bought a sharpening device.

Don't get rid of the broken blades until you have identified the problem.  Look for cracks at the transition area of the tooth and the gullet.  Look for cracks on the back of the blade.

[WH_Conley]

Tom pretty much touched all the bases, only thing else I can think of is to check set of the blades, not enough set would cause them th heat up.

[pigman]

I have on occasion found a log from a tree that has died and dried standing and is very hard. On the job I am on now I had a log that gave me fits. Tried three  different new blades and still could barely cut the thing.  The blade would dive,heat up and pull so hard that it would almost stall my 40hp motor. I finally was able to cut the thing with a .055 blade with way too much tension and cutting at a very slow rate. :( The rest of the logs cut normal. The point of this useless ramble is that a few logs are almost impossible to cut wit a bandmill.

[ARKANSAWYER]

  Open up the little door in the middle and look for a piece of bark or wood.  Alot of time it will be laying under or behind the blade and you will not see it unless you look for it.

 I have to change belts about every 100,000 bdft or every 4 months.  When they get worn they will cause a blade to break and wonder but not heat up. ???

  With a blade on and tightened up pull the blade backwards.   You should be able to pull it even with the brake on and the handle up.  Make sure the idle wheel spins freely when you have the blade off.

  A dull blade that is set right will cut straight but will with alot of heat.   One that has been flipped inside out and put on backwards will cut but get real hot.   If you get the blade under the ceramic guides it will cut but get hot.  (Sam did that one time not me)   If the ceramic guides are to tight will cause the blade to get hot.

 If you find some one who knows let us know so we can ask them when we get a question.   And I cut pine and oak with the same blade.   10 degree 7/8 0.045's

[Russ]

I don't know why your getting your blade so hot. If its getting plenty of lube  the the teeth are dull. The blade gets hot and its going to strech till it breaks.
I debark almost everything now, made a sharpener from a chain saw sharpener and they seem to cut alright after sharpened. It seems like I averaged about 500bf a blade on  logs with the bark still on, double on debarked logs. I lube with a sparse amount of keosene now. Good luck I know how it is when your having trouble keeping blades on.

[MartyParsons]

( Most of these guys have sawed more than I will ever think of. But here is my 2 cents worth of wisdom.)  Hi Tom and the others are right on track the only things I will add is that look at the blade and see where it broke at. If it brakes at the weld then we could have a dirty weld usually brakes during the 1 st cutting, if it brakes at the gullet it could be a flex life issue related to running the blade to long, if the blade breaks on the back of the blade it is rubbing the roller or a wood chunk is stuck in behiind the blade causing heat ( you will see lots of cracks on the back of the blade). Was your blade getting dirty with sap? Do you have the e-z glide pads or cermic pads on the roller guides? You will only have .008 to .010 clearance if the blade gets dirty that is gone and the blade will get hot quick. Pine has a Cabnium layer under the bark and these fibers are almost impossible to cut through and usually end up around the tooth and will remove the set on the tooth. Not realy remove the set just fill it up and give you a very wavy cut. Just try and do a skim cut across the bark on a pine log and you will see what I mean. I always give a heavy slab cut on pine unless my wife is off bearing.
Thanks Marty

[bull]

steam,smoke, burning rubber, red pine !!!   been there done that.........   Slow down, more water  pitch is a big problem / i use Dawn dish liquid in the lube mizer when cutting red pine, it cuts the pitch, if your blade dives in a clear log you are sawing too fast........   Never go from red pine to any other wood. Change the blade......  Maximum BF on blade cutting red pine 750 bfd....  I pull the blade around 500bfd even if it is still cutting good.
the blades that are braeking most likely have already been stessed.  Heated / over sawn - don't saw to dull and you will get more life out of your blades....