chain breaking

[joel logger]

Hello everybody. For the past few days I've been milling some gorgeous old growth red pine. Growth rings are super tight and the heartwood is spectacular. Everything is coming along fine and me and my friend is runnig 2 alaskans with 661 and a 36" bar. We've been ripping 1.5" slabs all day and the stack of freshly cut lumber is growing rapidly. Later on i start making the first cut on one of the bigger logs. And then when i go to rip the first slab off the log i get about 10" into the wood and all of a sudden the chain breaks. First time this ever happend to me so i figured i hit a nail. Got the tangled chain off and to my surprise none of the teeth showed any damage. Still sharp as a razor. I've hit nails before so i knew this was different. The chain had snapped the cutting tooth in half and i could hold the two broken ends together and they matched perfectly. I went to put a new chain on and finished the cut without any problems. There was no metal in the cut surface. We stack the slab and I go back for another cut. Got about 6" in the cut this time and same thing happens. Poof! I inspect the broken ends and its almost identical. Cutter tooth snappen in half. However this time I notice the rivet next to the tooth is stuck and wont pivot at all. Anyway I've inspected the bar and its dead straight. Mill is set equally on both sides. The sprocket is showing a little sign of wear but nothing major. Could it be the wood thats causing this!? Frustrating indeed having to end the day like this. Anyone got any ideas?

 

[BobL]

I doubt it's the wood. Are the two chains from the same roll? It could be a bad batch of chain.

What size/brand chain was it?

 

[Czech_Made]

Following.
Do other pivots on the chain move freely?
I would buy a new chain and give it a shot.
Also could you post more pictures of the pine, looks great.

 

[joel logger]

@BobL Sorry, forgot to mention that in my original post. Well both chains are Stihl ripping chain. 3/8 and .050 gauge. I believe i bought the chains at different occations. I did however put a grind on them the night before. I grind my chains 10 degrees cutting angle and 50 degree hook, and i've been grinding them that way for a long time now and never had them snap like this. And 2 chains breaking just minutes apart made me believe this is more than a coincidence. Perhaps i put too deep of a grind on them?

@Czech_Made yeah the other pivot just fine. I had the chains dropped at a repair shop today and ill be back milling on monday. Hoping they will hold. Oh and i'll make sure to take some more pictures too.

 

[BobL]

@BobL Sorry, forgot to mention that in my original post. Well both chains are Stihl ripping chain. 3/8 and .050 gauge. I believe i bought the chains at different occations. I did however put a grind on them the night before. I grind my chains 10 degrees cutting angle and 50 degree hook, and i've been grinding them that way for a long time now and never had them snap like this. And 2 chains breaking just minutes apart made me believe this is more than a coincidence. Perhaps i put too deep of a grind on them?

Side on photos ?

 

[blades]

Maybe you were grinding in to the off side strap- severely weakens chain integrity

 

[BlueRider]

I've broken 3/8 .50 before but I've never broken .404 .63. With .404 hitting something that will snap a 3/8 chain will break teeth off of a .404 but it won't break it. The difference in kerf is only about .010" (.25mm) so in my mind its not worth not using .404 , particularly with a big powerhead

 

[joel logger]

Got the chains back yesterday and went milling again. Only got two slabs cut before a massive rain storm shut me down for the day. The chain didnt break, so thats good i guess. @BlueRider you make a good point, thanks for the tip.

 

[CR888]

Two similar failures so close together is a bit odd. The rivets probably bound up when the chain broke. Unusual.