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Jimping causing cracks

S

Skiller1nc

Joined
Jun 27, 2016
Messages
302
I did 2 separate runs of some d2 hunting knives recently and added jimping to all the spines. I'm using a standard 20 something TPI grobet jimping file. On 8 of the 37 total knives I have cracks running perpendicular to the edge, originating at the jimping grooves. Obviously, this makes sense as the jimping is causing stress risers but I have not heard of anyone else having this issue. It effectively rendered 20% of my blades useless. Has anyone else noticed this issue? Do I need to just move to round diamond files post ht (that would be awful)
 
It makes you wonder if they will fail in the same spot while in the customer's hands.

It's another good reason to skip jimping.

If you had to do it
I think 20 is too coarse.
I think round bottom notches are better than sharp.

Who did the HT ?
 
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I like to temper the spin back after HT and then use a jimping file to put them in. (Though the file won’t last as long that way)
That‘s just my two cents though.
 
Whoa slow down here…. Explain your process. Let’s not make sweeping declarations here

These are done on a surface grinder post heat treat. This is not my work, but this maker has been doing this for many years
LgvBJYd.jpg
 
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Me explain my process? I take an annealed knife (all of these were d2), clamp it in vice, and file the jimping (my order for the file says 20 lines per inch) until it's as deep as the file will go. then I grind my bevels, oven/foil/plate quench/cryo following knife steel nerds recommended temps and times I don't recall them off the top of my head, 2x2 temper tested at 61rc and then surface grinding where I then see cracks. smack blade and it breaks along the cracks. grain is fine, and if I smack or twist non-cracked blades they are fine.
 
Skiller1nc said:
Me explain my process? I take an annealed knife (all of these were d2), clamp it in vice, and file the jimping (my order for the file says 20 lines per inch) until it's as deep as the file will go. then I grind my bevels, oven/foil/plate quench/cryo following knife steel nerds recommended temps and times I don't recall them off the top of my head, 2x2 temper tested at 61rc and then surface grinding where I then see cracks. smack blade and it breaks along the cracks. grain is fine, and if I smack or twist non-cracked blades they are fine.
Click to expand...
You could try a snap temper in between the quench and cryo, see if that helps.
 
Skiller1nc said:
I did 2 separate runs of some d2 hunting knives recently and added jimping to all the spines. I'm using a standard 20 something TPI grobet jimping file. On 8 of the 37 total knives I have cracks running perpendicular to the edge, originating at the jimping grooves. Obviously, this makes sense as the jimping is causing stress risers but I have not heard of anyone else having this issue. It effectively rendered 20% of my blades useless. Has anyone else noticed this issue? Do I need to just move to round diamond files post ht (that would be awful)
Click to expand...
Yes they are stress risers but you have just 8 of the 37 total with crack? If you have 37 total knives from carbon steel and probably some of them will bend after quenching .Why not all of them ? My point is not all bevels are perfectly symmetrical grinded .Some of them is enough close to perfect so some will take wrap some no . Same is with jimping .And maybe not perfectly symmetrical bevels can contribute to crack originating at the jimping grooves .
If I ever do jimping I will do that after hardening , I have no doubt in that .In fact now I am hardening rectangular piece of steel , after that I shape a knife from that , drill holes and grind bevels ..........
 
This might be tricky for a steel that needs to be plate quenched, but what about putting in the jimping pre HT then coating the spin with something (like satanite) to help it to cool down more evenly in that area?
 
If you're doing a low temper tweak with D2 you do not want a snap temper between quench and cryo. <--- this is one of the primary reasons it developed a reputation for poor edge stability. And if you're not doing a low temp tweak with D2, I wouldn't I use D2...

It has a brittle failure mode and it benefits from a relatively rapid quench (not a sloooow air quench). With that in mind, I would put the jimping in after HT and I would want a radius in the bottom of the cuts.
 
Nathan the Machinist said:
If you're doing a low temper tweak with D2 you do not want a snap temper between quench and cryo. <--- this is one of the primary reasons it developed a reputation for poor edge stability. And if you're not doing a low temp tweak with D2, I wouldn't I use D2...

It has a brittle failure mode and it benefits from a relatively rapid quench (not a sloooow air quench). With that in mind, I would put the jimping in after HT and I would want a radius in the bottom of the cuts.
Click to expand...
so what are the options for doing this? diamond files/burrs, carbide endmills? I don't have access to a mill so does that just leave either filing one groove at a time by hand or using something like a rotary tool with a burr?
 
Interesting, I've made a lot of knives in D2 with jimping made with a small round chain saw file prior to heat treatment and never had a problem. The sharp corner of a checkering type of file would be a higher stress point.

Did you heat treat a bunch in a row? Use water to cool your quench plates (water on the quench plate)? Full flat grind into the jimping maybe? Just throwing out some ideas.

Depending on your stock size you could drill a row of small holes for the jimping, then grind away the excess.
 
Drilling the holes could work, I had these waterjet but I could add sacrificial material next time, I guess if I'm working them annealed I could use a round file easily enough, I just love the look and feel the file and 20 TPI leaves. Yes I heat treated a bunch in a row, 16 at a time, plates were water-cooled and dried after each set of quenches (I quench 4 blades at a time), no grinding into the jimping the primary bevel only came halfway up pre HT
TILLER said:
Interesting, I've made a lot of knives in D2 with jimping made with a small round chain saw file prior to heat treatment and never had a problem. The sharp corner of a checkering type of file would be a higher stress point.

Did you heat treat a bunch in a row? Use water to cool your quench plates (water on the quench plate)? Full flat grind into the jimping maybe? Just throwing out some ideas.

Depending on your stock size you could drill a row of small holes for the jimping, then grind away the excess.
Click to expand...
 
Skiller1nc said:
so what are the options for doing this? diamond files/burrs, carbide endmills? I don't have access to a mill so does that just leave either filing one groove at a time by hand or using something like a rotary tool with a burr?
Click to expand...
smart kid ;)
 
I had it happen once on some thick A2 once. It freaked me out. Then i noticed that all the cracks came where I didn't grind the plasma cut esge back. The A2 also got orange peel at 120 grit and had a qeird pattern when I etched it. So far I have never had problems with smaller knives. Your steel and how it was cut can matter and is worth checking
 
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