Chipper knife failure

[baumeister]

Trying to figure out if this was from over tightening or from not being tightened down.

I am guessing the one odd looking bolt had the answer. Is there anyone out there that can tell me what the failure process had to be I. Order get that type of deformity?!??

I have a hypothesis but am curious if you guys agree.

 

[Tom Dunlap]

How often had you replaced the bolts?

There is a spec about reusing them. If I recall it's under five times. The bolts get stretched and twisted.

You might be able to get an answer by talking with a nut and bolt supply house

 

[chiselbit]

What other damage did it do?

 

[Reach]

My thought is that these bolts have been shears off, this is not a torsion break, which is what would happen if they were over tightened. They may have not been tight enough/not even screwed in all the way and then sheared the heads off on the anvil. Or the anvil moved and hit them, although this is unlikely as the anvil would hit the knives first unless your knives had been ground down well past the allowable limit.

Random useless fact: Grade 8 bolts will shear off with less force than Grade 5 because they are much harder, however they have a greater tensile strength making a torsion break more difficult.

When did they break, at the moment the clutch was engaged, or had the chipper been running a while?

 

[Joeybagodonuts]

Daaamn dude!
What's the knife look like? Do you even have it still?
I've heard some myths & rumors about what can happen if knives arent properly installed & swore if it was going to happen, it would have with on this old BC1000 we used to work with. Those bolts were soooo oblonged, stretched & over tightened i cringed every time we started it up..

At first glance they don't look to be all stretched out or anything.. That oddball one looks bent & sheared so maybe they werent tight enough & it was the last to go??? What was your hypothesis anyways? Did i glaze over it?

 

[southsoundtree]

Torque wrenches tell the truth. Torque specs, your friend, fatigued bolts, not your friend.

 

[oldoakman]

Torque wrenches tell the truth. Torque specs, your friend, fatigued bolts, not your friend.

X2

 

[Jeff]

X2

X3

 

[Joeybagodonuts]

Torque wrenches tell the truth. Torque specs, your friend, fatigued bolts, not your friend.

X4

5ft cheater bars, not your friend.. ever!

I'd like to know what happened here as well as what other damage happened because if it like a few others have asked..

 

[TimberJack]

Tell us what brand of chipper these bolts are from and a bit of the maintence log of the machine to paint a clearer picture.

 

[chiselbit]

And show us some pictures of the carnage

 

[Treetopflyer]

The suspense is killin me

 

[Pelorus]

Dusclaimer: I have changed knife bolts & nuts exactly 1 time since buying my Bandit 65XP in 2006 (The hour meter broke years ago with 1800+ hours on it.) Have never used a torque wrench on them bolts. I'm just a lucky guy is all.

 

[Treetopflyer]

65 xp I'll buy it the substance of larger wood is impressive , not that 6 inches is anything to bok at!

 

[Chaplain242]

If look at end view picture, the second bolt was corroded across half the bolt, and also down near the threads, the other half of bolt is torn off (head snapped off). Without seeing the heads, or the blades, I would guess that bolt head snapped off first, then the one next to it, until the last ones had enough leverage to lift/shear to cause the distortion you see.
Possibly initiated by overtightening, but if a long time since they were tightened could also be too tightened too many times - enough to cause hardening and continued use causing a crack across the bolt at the head junction.