Troubleshooting Bandmill Blade Breakage

What causes bandsaw mill blades to break after one or two sharpenings, and how to prevent it. March 29, 2006

Question
I recently bought a Timberking B-20, new. Iíve cut about 15 M ft of SYP and broke 18 blades. Almost all broke after the first sharpening. Iím using running water with soap. I donít think Iím running too fast. Does anyone have any advice?

Forum Responses
(Sawing and Drying Forum)
From contributor A:
You are setting the band too, right? If not sharpening correctly, this will also cause breakage. Always set it after sharpening. De-burr the band before setting, or it will give an improper set. Water should not be used, since it will cause your blades to rust. A band needs lubricant, and this makes a big difference. Try running 50/50 mix of diesel fuel and bar oil. Depending how cold it is, you might want to increase the diesel ratio. If the blades are getting too hot to touch, you have a problem. Some mills are not running blade speed fast enough .Slow blade speed will cause bands to run hot. Also, too much blade tension will cause breakage. What guides are on mill? Guides play a big role in blade life. Running dull blades shortens their life. It is better to sharpen more often, and it really extends blade life. Originally I had your problems, breaking bands all the time. Blade speed, lubricant, and attention to the guides cured my problem.



From the original questioner:
I'm having blades professionally sharpened. At first we ran till the blade waved. Then we started changing every 2 hrs. Blade tension is at 1200 lbs. (factory specs) and the use of water was also recommended by the factory. I am not really familiar with the guide specs - they came on mill, steel with grooves. Could I be running too slow and overheating them? If so what feed speed should I run? The factory man said run slow and save the mill. I even tried buying blades from different source - sharpened 4, broke 2. Itís got to be something I'm doing wrong.


From contributor C:
Try setting blade tension at a 1000 and see what happens.


From contributor D:
I have a Kasco saw 2B and my manual says 400-500 lbs blade tension. My dealer recommended 700-800 lbs blade tension. I have only broken a blade by hitting some steel. I have been sawing 1-1/2 years and am still using a few of my original blades. I sharpen them myself.


From contributor E:
Check your guides. With the blade tensioned rotate the band wheels by hand and check the clearance between the flange on the guide roller and the back of the blade. The clearance should be less than 0.025 inches.


From contributor F:
I also run a B-20, mostly hardwoods. One thing is not to walk away for lunch without taking the tension off the blade. If I mess up and leave the blade tensioned overnight the blade always breaks within the next 10 minutes or so. The heating and cooling is tough on them. I also notice pitch build up when I saw EWP. I run pine sol at 2 cups per 5 gal. If you are not using the lumber indoors you might try the fuel lube as previously suggested but it gets pretty nasty to smell all the time, and the customer might object.


From contributor G:
Are the breaks occurring at the weld or at random locations? Have you broken any new blades or just resharpened blades?


From contributor H:
I had the same problem until I spent an hour getting my bandwheels co-planar. Before I aligned them, I'd get 2 sharpenings. Since I aligned them, I'm getting 4 or 5, and still haven't broken a band. Lay a piece of straight aluminum, or a straight level across the bandwheel above and below the axles. The bandwheel edges should each touch the straight edge. If they don't the wheels aren't co-planar. My mill (Timber Harvester) has an adjustment that can be made on the idle wheel to move the bandwheel face in or out. It's just a bolt with a lock nut on it. Yours is probably very similar.


From the original questioner:
Thanks for the input guys. I've made some adjustments and changes as you've mentioned and I'll keep you posted.


From contributor I:
I own the largest portable saw mill company in the state of Washington. The reason why youíre breaking blades is that you have to grind the whole tooth, not just the face. Gullet cracks develop when the blade starts to get dull. You can not see them except with a microscope. There needs to be .005-.010 of material removed from the gullet every time the blade gets sharpened. If you don't, they break. I sharpen my blades 15 to 20 times before they break. Every 2 to 3 sharpening they need to be set at .019 to .021. The best sharpener and setter are from Cook's Saw.


The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor T:
Proper tensioning of the blade is a must and can best be accomplished with a blade tensioning gauge. I have one from Lenox and it has solved a host of problems. Also as stated before, the blade wheel must run in the same plane and this must be adjusted with the blade under tension. Then re-check the tension. I have used diesel fuel mixed with 25% chainsaw oil for 10 years now and have never had a complaint about staining. Just remember, don't use this on kilned wood and keep the blades sharp.