Broken chain, common occurrence ?

[bmp01]

Newbie to milling question about chain life really. Would you expect to get the full tooth life out of a chain used for milling or is it typical to bin the chain after say a 1/2 or 2/3rds tooth wear ? Let's assume no chain damage through its life, just wear.

Reason for qu - I've busted an Oregon 75DPX chain where the chain has been used for milling the majority of its life. To be honest it doesn't owe me anything, for the cost of the chain I've milled a good deal of oak. But well ye know the chain teeth still look very servicable and the links still feel pretty tight.

Power head is a tuned up Husky 395XP, chain is  Oregon 3/8 regular, chamfer cutters, ground to 15 degrees. Chain did see some metal a while back but very minor just dulled the teeth and quickly fixed with routine file sharpening. Failure was through the preset joining link which always makes me suspicious. I'll see if I can find a picture.... 

 

Thanks for any input. 

[bmp01]

[AJStrees]

4 minutes ago, bmp01 said:

Haven't had a chain break from milling. Has the chain broken more than once in the same place or difference places? Try a new joiner. Also how is your oiler doing during milling? Is the chain overheating at all?

[trigger_andy]

Only ever broke one chain and that was almost maxing out a 60” bar in oak so I can not really complain. Brand new though.  It will mend. 

[bmp01]

Just once so far. I have some joiner links arrived today. But also wondering about new chain if its going to break often from now on.

Chain and bar not getting hot but they do look 'dry' to the point that after each plank I run the saw out of the wood to ensure chain is thoroughly oiled. Its oak that's been down for 5 years or so, still damp in the heart wood though. Auxillary oiler would be an advantage...

[AJStrees]

10 minutes ago, bmp01 said:

Just once so far. I have some joiner links arrived today. But also wondering about new chain if its going to break often from now on.

Chain and bar not getting hot but they do look 'dry' to the point that after each plank I run the saw out of the wood to ensure chain is thoroughly oiled. Its oak that's been down for 5 years or so, still damp in the heart wood though. Auxillary oiler would be an advantage...

Well try the new joiner. Unless the chain you are using is cheap metal or getting over heated, then it shouldn't keep breaking. I have an aux oiler. But it generally stays in the shed, don't need it. Doesn't seem to make much of a difference on the 881. 

[openspaceman]

@bmp01 I can't comment on milling as I didn't do hardly any with a chain but it strikes me cutting down the grain is harsher than across.

 

Which order did the tie straps break? I generally noticed the problem of one side failing before the lot let go.

 

When I did break chains it was almost always   at the joining link and I put this down to lack of support as the rivet was spun. Also the factory  riveters really thump the rivet as  it is spun whereas the manual spinners spread the rivet head without that much pressure, I hope @nepia doesn't come across this problem with my recent efforts.

[nepia]

Me too (!) Andrew but you were good enough to warn me of the potential weakness; thanks

 

 

[bmp01]

Thanks for the comments AJStrees, trigger_andy, openspaceman.

 

Openspaceman - Interesting observation regarding rivetting technique. ... enlightening even.....

 

Ok, well the failure happened in an instant, engine revs went skyward that was the first I knew. No half measures - one length of chain rather than a loop.

I used to look at failed bits of engines, searching for clues as to what went first so I'm reasonably in my comfort zone in anslysing the bits. I found fatigue patterns on the preset link which tells me it had a crack in it that was opening (and closing) each load cycle, with crack growing over thousand of cycles. The tie link has pinged, the material was stretched to the point of snapping. The remaining bit of tie strap is a cock-in-a-sock fit on its rivet, this could have happened in the failure but there is no sign of that .

So the conclusion is the preset cracked first, crack grew and finally broke, tie link followed shortly there after. But why?

If the rivetting is done well - so lots of pressure as well as rolling of the head - its likely the pin through the tie link is expanded within the tie link as well...so it takes up any radial clearance between the two parts. No clearance means the tie link can do useful stuff like taking its share of the load in the chain. 

Conversely, poor rivetting leaves radial clearance between rivet and tie link, so tie link cant take any load - the preset link does all the work, continually bending back and forth and fatigues.

 

So the redneck use a hammer for rivetting rather than the pukker rolling tool doesnt seem so bad after all.... 😨😀

Edited June 26, 2022 by bmp01
Corrections

[openspaceman]

I think I agree but need to clarify your naming convention. The preset is a tie strap with the rivets already set in it, the loop is closed and a second tie strap is then place over the rivets and the rivet is spun. If the rivet is first forced hard then the new tie strap is fixed securely to the rivet, with the rivet now fully expended into the tie strap hole  and the increased friction between the rivet shoulder and tie strap adds strength, it also reduces any play.

 

I wonder if there is play then the one of the tie straps can flex. This flexing could fatigue and snap the tie strap in the middle,  the extra stress then straining the weakest part of the remaining tie strap at the rivet??