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Recommendation? Butter Dive Knife

D

David Fletcher

Joined
Aug 18, 2018
Messages
2
Hello everyone, I make knives as a hobby for about 2 years now, and I wanted to make my neighbor (who's a diver), a dive knife. However, the steel would just rust. I never use barstock, only reclaimed metal like lawnmower blades or edger blades especially. Anyway, I got a stainless butter knife at a yardsale for $.50, and I plan to heat it to around yellow white and quench in water after shaping and drilling. Will this make a blade of any value or will it just be of no use beside the occasional cut?
 
David Fletcher said:
Hello everyone, I make knives as a hobby for about 2 years now, and I wanted to make my neighbor (who's a diver), a dive knife. However, the steel would just rust. I never use barstock, only reclaimed metal like lawnmower blades or edger blades especially. Anyway, I got a stainless butter knife at a yardsale for $.50, and I plan to heat it to around yellow white and quench in water after shaping and drilling. Will this make a blade of any value or will it just be of no use beside the occasional cut?
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Depends on the steel. More than likely the butter knife is case hardened out of a very low grade alloy. I doubt heat treating it would make any difference.
 
So first recommendation, ask here: https://www.bladeforums.com/forums/shop-talk-bladesmith-questions-and-answers.741/ , it's more specialized and the people are more knowledgeable than I am.
Secondly, I can't see it working for numerous reasons, first a Butter Knife is generally very thin, so the chance that it warps or breaks are quite high. And then even if it works it's gonna be a pretty small knife with a small handle and you'll have to make a sheath for it, I don't know if American butter knives are different but to me I wouldn't want one as anything other than a butter knife, especially if it's something my life might depend on it.
The thought to make a gift for a neighbor you like, especially something personalized related to a passion/hobby of is should definitely be commended.
You might want to look into N680, N690 or N695 Bar Stock, H1 and LC200N seem to be hard to come by. Or some Knife Blanks in that material, or some equally decent stainless and modify it to personalize it more. It will last a good long while, especially if he maintains it properly.
 
Dive knives are typically softer steel to maximze retention of both toughness and stainlessness, more then actual "edge holding". Even H1 and dendritic cobalt which don't rust at all, and are marketed mainly as great saltwater/sea blades, are softer alloys then many others.

That said, I'm guessing a cheap butter knife is probably some low grade 420j2 or 403 type stainless steel already. Tough and stainless enough, but just won't hold an edge super long... Soft by stainless knife steel standards already, if you are adamant and determined about making a butter knife into a dive knife, the stock is already ground thin enough, just break out the old school hand tools and cut & file it to your design, put an edge on, and skip a re-heat treat step altogether. Just focus on a handle and sheath...
 
A dive knife should be for cutting rope, netting, tough kelp, etc., not for prying. For prying, get a titanium pry bar. A good dive knife will have either a combined serrated/plain edge or a plain edge on one side and a serrated edge on the other side. It will be hardened to at least Rc 60 to hold a good edge for a decent time. There are several stainless steels which are suitable, among which are M390, Elmax, S35VN. All are in the 17 - 18% chrome range and have 3 - 4% vanadium which adds abrasion resistance. All of this is just my humble opinion. I'm sure there are others who will recommend a 1/4" thick bar with a 45* edge of Rc 45 Stainless which is easy to sharpen underwater with the sharpening stone hung off your belt and which is great for prying mussels off rocks. Won't cut shit, though.
 
First I would ask him what he uses a dive knife for. Cutting rope? Prying? Stabbing sharks? That lets you know where to focus. Second I would ditch the butter knife and consider modifying a bar of titanium, especially if he dives in salt water. Titanium is totally rust resistant and can pry and with round serrations should cut rope decently. It doesn't have great edge retention but divers generally don't do a huge amount of cutting in one sitting unless they happen to come across a whale trapped in a fishing net
 
Just to add another reason why the plan for the butter knife won't work is your projected HT. Stainless steel would be ruined in an open chamber forge and HT as you described. It has to be secluded from oxygen and held at around 1900-2000°F for half an hour to be properly hardened.

I would get a bar of S35VN and make the knife and then send it to someone for HT.
The other option is to make it from titanium and have no HT. Grinding titanium is not for inexperienced makers, as you can damage your eyes and set the shop on fire.

My preferred shape for a 6" long blade dive knife is a rounded tip dagger look about 1.5" wide and 3/16" thick. I serrate the last 3" on one side for cutting rope and kelp. The edge and tip are ground at a rather steep angle of 40° inclusive to make them tougher. You don't need a razor sharp knife for diving, as it would be more likely to cut you. A dive knife only needs to be sharp for a short while, as you usually touch the edge up before each dive session.
 
kuraki said:
There are probably more efficient ways to kill your neighbor, but this way will look like an accident.
Click to expand...
I probably laughed a little too hard at this comment...

To the op, I also suggest titanium if you want absolute rust resistance in salt water . If your friend takes good care of his gear, something like s35vn would work perfectly. He just needs to clean his knife with soap and fresh water when he gets out of the saltwater.
 
I'm not a diver, I don't know if anyone else here is either, but I seriously doubt that a butter knife will make a good dive knife no matter what you do to it. If it were me, I'd do my research and figure out what steel dive knives SHOULD be made of, and buy some of that. Then have it professionally heat treated since stainless HTs are more complicated than the backyard smith can do.

Diving is dangerous. I wouldn't trust my or another person's life to some jankey butter knife.
 
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