post-HT grinding on wide blade blade

E

EGA

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Apr 12, 2018
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Working on a 7" santoku, 1/8" 1075/1080, stock removal.

I've gotten the blade down to approximately the correct proportions for heat treating, it'll be about 0.030" at the edge before HT, but I want to get it down even thinner, which I'll be doing after HT. Since it's a flat grind on the entire width of the 2" wide blade, is there any reason at all for me to go beyond 60 grit I heat-treat? I'll be taking the edge and the tip down in thickness after HT. I had planned to do that work with 60grit, though perhaps I should be doing it with something like 220.
 
I like to go to 120 grit prior to HT on simple steels like 1080, but I think 60 is OK. Just make sure the scratch pattern is lengthwise ie:tip/tang, and not spine/edge. Because you will be doing a lot of material removal post HT, no need to go much higher. I just did a couple Cru Forge V blades yesterday at 80 grit, scratch pattern lengthwise, no issue at all. However, I do sand the very edge down to 220 grit (not the entire blade, just the edge). Probably not necessary, but for peace of mind.
 
samuraistuart said:
I like to go to 120 grit prior to HT on simple steels like 1080, but I think 60 is OK. Just make sure the scratch pattern is lengthwise ie:tip/tang, and not spine/edge. Because you will be doing a lot of material removal post HT, no need to go much higher. I just did a couple Cru Forge V blades yesterday at 80 grit, scratch pattern lengthwise, no issue at all. However, I do sand the very edge down to 220 grit (not the entire blade, just the edge). Probably not necessary, but for peace of mind.
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Thanks. I keep trying to find a reference that explains why the scratch pattern should be lengthwise, especially pre-HT. Any ideas?
 
EGA said:
Thanks. I keep trying to find a reference that explains why the scratch pattern should be lengthwise, especially pre-HT. Any ideas?
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It is because of stress risers and cracks. A blade is much more likely to crack edge to spine following a deep scratch than it is to split from tip to tang, especially due to the different cooling speed created by the bevel.
 
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Grayzer86 said:
Iran because of stress risers and cracks. A blade is much more likely to crack edge to spine following a deep scratch than it is to split from tip to tang, especially due to the different cooling speed created by the bevel.
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I see, thanks. That makes sense. Hard to do tail-to-tp on a vertical belt sander. I guess that part will be done by hand.
 
The "stress riser" thing is way overblown on knife blades. In gears and mechanical parts it is a big deal, but on flat and simple things like knife blades the depth of a grit scratch is insignificant. The only place it might mater would be a sharp 90 degree angle at the tang.

I sand to 120 grit on most, and 220 grit on thin blades .... if I bevel at all before HT.
 
Related question to post heat treat grinding, on a narrow fillet blade 0.06-7” Aebl stock 61-62 rc. If no beveling done pre ht, is it best to just start grinding bevels with 36 grit, or higher? I don’t have a wet grinding setup but will dip every pass to try and not mess up temper. Just wondered where folks start, will be my first post ht grind on something that thin and narrow. and heard aebl can warp here
 
knoxknives said:
Related question to post heat treat grinding, on a narrow fillet blade 0.06-7” Aebl stock 61-62 rc. If no beveling done pre ht, is it best to just start grinding bevels with 36 grit, or higher? I don’t have a wet grinding setup but will dip every pass to try and not mess up temper. Just wondered where folks start, will be my first post ht grind on something that thin and narrow. and heard aebl can warp here
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I do a lot of fillets lately in AEB-L and CPM154 at that thickness. All my grinding is done post heat treat. Other may differ but for these blades I start with a good sharp 50 grit ceramic. I tried a 36 once but found it far too aggressive for me.
 
I have HTed plenty of blades ground to 60 grit. I generally kill any burr/slightly round the edges with a fine cut file. I have only had one HT crack, on a Nakiri in 1095 quenced in #50. I had ground it thin, had a clayed spine, etc. The lesson I learned was more about blade thickness especially in conjunction with a differential heat treat than about grit.

I may be wildly wrong and have just gotten extraordinarily lucky, but I suspect that the time you save by not patterning lengthwise scratches or adding another grit or two to your pre HT grinding is greater than the time you lose forging one new blade very occasionally. If you are doing stock removal on something other than damascus or san mai, I can't possibly imagine that adding stepps to your grinding process will save time in the long run.
 
thank you stacy and grayzer86. Will start with either 50 or 80 when i get my blades back in (hopefully) a few weeks
 
I agree with Stacy. I go lengthwise just for peace of mind, and have never had an issue doing so. You probably could get away with 50 grit vertical scratches, all the time. I don't know that for a fact tho. And I would think faster quenches with the shallow hardening steels like 1095 and W2 may be more of an issue, but likely not.
 
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