Backspring snapped any help?

UAB89

UAB89

Joined
Jan 5, 2015
Messages
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Hey guys so I had a knife that the backspring snapped when closing the knife about and inch from the top I was wandering if y'all had any idea about what might have been the cause?

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There are some pretty deep scratches on the sides that may have caused stress risers. Maybe the scallops cut in what I assume is the inside of the spring contributed to the break. Also the spring temper may not have been correct. I am sorry this happened to you but it could be a learning experience if you built this knife.
Nathan
 
navin74 said:
There are some pretty deep scratches on the sides that may have caused stress risers. Maybe the scallops cut in what I assume is the inside of the spring contributed to the break. Also the spring temper may not have been correct. I am sorry this happened to you but it could be a learning experience if you built this knife.
Nathan
Click to expand...

Thank you for the help Nathan!


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Don Hanson III said:
Could be a number of things, but I sure would not put those scallops on a spring.
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Thanks for your response Mr Hanson I have never seen one to do that and was also wondering if it was related to the scallops or To high of RC from heat treat..?


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I agree with Don,I wouldn't put those small scallops on the inside of a spring. My SWAG that it snapped in the middle of one of the scallops, that was probably where the main flexing was taking place causing a failure.
Imake my springs so they a long gentle curve from center pin to pivot,kind of like a leaf spring on a car.
 
UAB89 said:
Thanks for your response Mr Hanson I have never seen one to do that and was also wondering if it was related to the scallops or To high of RC from heat treat..?


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Could be too high RC, and/or the tang lifting the spring too high, spring too short, the scallops.

I also agree with SBuzek.
 
Thank you all for your responses


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Personally I don't think there is anything you could do to the blade to cause this,other than removing it and changing the geometry of the tang.
Grinding off the kick will make the blade hit the spring at times but that should not cause a failure other than your edge.
Would you post a pic of your mod so we can see what was done. You can black out the makers name if you wish or take it from the pile side.
 
SBuzek said:
Personally I don't think there is anything you could do to the blade to cause this,other than removing it and changing the geometry of the tang.
Grinding off the kick will make the blade hit the spring at times but that should not cause a failure other than your edge.
Would you post a pic of your mod so we can see what was done. You can black out the makers name if you wish or take it from the pile side.
Click to expand...
Agreed again. & Yes a picture would help.
 
SBuzek said:
Personally I don't think there is anything you could do to the blade to cause this,other than removing it and changing the geometry of the tang.
Grinding off the kick will make the blade hit the spring at times but that should not cause a failure other than your edge.
Would you post a pic of your mod so we can see what was done. You can black out the makers name if you wish or take it from the pile side.
Click to expand...

Don Hanson III said:
Agreed again. & Yes a picture would help.
Click to expand...


This was after my mod and actually right after the spring snapped as I was closing the knife

Thanks again




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Photo helps a LOT - and to be sure, the "mod" you refer to is making that "Vee" a tad deeper/larger? No way that would have anything to do with backspring breaking - "IF" I'm understanding correctly. BUT - the real pros will chime in and comment. Don and SB are the thru experts.
 
You made that V deeper/wider? Or did you grind off the 'kick' that makes contact with the spring when closed?

Either way, this should not cause the spring to break.
 
Don Hanson III said:
You made that V deeper/wider? Or did you grind off the 'kick' that makes contact with the spring when closed?

Either way, this should not cause the spring to break.
Click to expand...

Hey I made the v slightly deeper and wider by grinding away a small sharpened portion of the base of the blade i don't believe I actually ground the kick at least not on purpose but good to know that either way it should not affect the backspring in your opinion! Thanks Mr. Hanson


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UAB89 said:
Hey I made the v slightly deeper and wider by grinding away a small sharpened portion of the base of the blade i don't believe I actually ground the kick at least not on purpose but good to know that either way it should not affect the backspring in your opinion! Thanks Mr. Hanson


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Click to expand...
Gotcha... The maker should fix the spring.
 
Yep I agree with Don,no way did that cause the spring to break. Maker should replace the spring IMHO.
 
Almost always too high RC . Only other is too much preload on the spring. Scallops didn' help . I have made just under 2K slipjoints and broke two springs due to too much preload on one and wrong RC on the other.
 
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