Trap Spring Knife Question

[BrownBear]

I recently fashioned a small patch knife from the spring of an unused Oneida Victor #0 single spring trap. Since I wasn't sure about tempering, I shaped the blade by hand rather than heating it up with a grinder. Settled on a tapered "dagger" style with both sides sharpened, just in case it wouldn't hold and edge and turned out to need tempering.

It took a heck of an edge--- Shaving sharp and it will cut ticking in a single easy swipe. I haven't tried cutting anything else with it, but so far I'm getting the impression that it might hold an edge just fine.

Now the question- Should I go ahead and temper it, and if so, how?

 

[ameling]

If you shaped it by hand and did not get it too hot to hold in your fingers (or hot enough to start turning blue/purple) then the original heat-treat and temper from the spring is still there. And you should not have to worry about heat-treating it again.

But to heat-treat it, you heat it up hot enough that it starts to glow red. As it heats up in that "red" stage, it will reach a point at which a magnet will no longer stick to the steel. That is the "critical" temperature for heat-treating. You then quench it in water, or oil - which would probably be better for that type of steel. It will now be about as hard and brittle as you can get it. Now you need to "temper" it so that it is not so brittle. Polish up a section of the blade - so you can see bare steel, and watch the heat colors run through it. Then slowly heat it up - mostly as far from the cutting edge as you can. As the blade starts to heat up, you will see that bare steel start to turn colors. First a "straw" yellow, then on into "robin's egg" blue, on to darker blue, and eventually to dark purple. When it gets around that robin's egg blue or a touch darker, then you quench it again. This makes the steel less brittle/hard, yet still hard enough to take and hold an edge pretty well. But you will be watching that color change right along the cutting edge. The areas away from the edge will get hotter, and will be softer. But that will make the "tougher" and less likely to break.

A search of the Knife Maker web sites will give you better instruction than this quick tail. That heat-treating and tempering gets pretty complex, with lots of stuff going on internally with the steel itself.

But if you didn't get that spring too hot when you were working it to shape, it should still have that original "spring" heat-treat, and will probably do well. Use the blade for a bit to see how the edge holds up, and how easy it is to re-sharpen. It might be well enough right now.

Just my humble rambling thoughts to share. Take them as such.

Mikey - yee ol' grumpy German blacksmith out in the Hinterlands

 

[BrownBear]

Just what I was looking for Mikey! Thanks, and I'll come back to it if it turns out I need it. I just shaped the blade by hand with a file, then polished it on a bench stone. First time out I cut a bunch of patches at the muzzle and afterwards it would still shave my arm with almost no drag.

Just today I did a little whittling with it, and though it still shaves, there's more drag and it leaves a few hairs behind. About as good as most of my other knives as a matter of fact, so maybe I won't have to try my hand at tempering just yet.

 

[paulvallandigham]

Cutting both paper and cloth can be hard on an edge, because there are silicas in the cloth " sizing " and granite dust in paper that wear the edge microscopically. Use a fine honing stone to freshen the edge on that blade, and then, STROP it on a leather belt to smooth the edge.

Stropping is critical to remove the " Drag " you report feeling in the dulled blade. Drap is the result of the fine edge being bent into a wave, rather than a straight, edge. This is the FIRST " warning sign " that the edge is being dulled, and could use another couple of strokes on the strop. If ignorred, the next " warning sign " is hairs, and " fuzz " clinging to the edge. That is evidence of actually tears, and breaks in the edge large enough to hold the fibers. By that time, you need a few strokes on a hard Arkansas, or equivalent hone, to bring the edge back.

 

[ameling]

It surprises many people just how good a cutting edge you can get and keep on high carbon steel without any heat-treating.

If you take a piece of that 1095 steel, and file/grind/sand a cutting edge on it, you will end up with a pretty good cutting blade as-is. It won't be as good as a properly heat-treated knife blade, but will be very ... servicable. Yes, it will dull faster in use and need to be sharpened more often, but will still be a good "user" edge/blade.

If you did not heat up that trap spring at any time, then that is just what you did in making your little knife. That original spring has lots of carbon in it, yet was heat-treated softer than a normal modern knife blade - to work better as a spring. It was getting most of its "springiness" from the carbon in the steel itself. And the fact that it was heat-treated kind of soft showed up in you being able to file it by hand.

A lot of the old farm/kitchen carbon steel knives were heat-treated a little softer, and could be sharpened with a file. The cutting edge did not hold up in use as long, but it was less "brittle", didn't crack/chip as easily in use, and could be sharpened fairly easily. Many people prefer a "working blade" like that. The little extra work of touching up the edge on a steel or stone is just part of having that good working edge/blade.

It does remind me of a quick demo a Master Bladesmith did of the main "tasks" required of a knife to pass the entrance tests to become a Master in some of the knife making organizations. He took a chunk of common welding-shop steel, quick ground a cutting edge on it, polished/honed the edge on his buffing wheel, and then did the various "tests". He cut a free-hanging 1 inch rope in one cut. He flexed that "blade" that 5 or 10 degrees without it staying kinked. And he clamped it in the vise and bent it a full 90 degrees without it or the cutting edge breaking. Those were the main "tests" to pass. The other "tests" were all in how it looked and was finished - even bevels, tight blade/handle fit, etc. It really took a lot of the myth/mystique out of those "bladesmith" societies. And was his way of ... spoofing ... those old-guard "protecting my turf" judges and big-wigs in the knife making organizations.

Just a few humble rambling thoughts to share. Take them as such.

Mikey - yee ol' grumpy German blacksmith out in the Hinterlands

 

[BrownBear]

Just a few humble rambling thoughts to share. Take them as such.

Rambling is good. Probably due to the shape of my mind, I seem to learn lots more from rambles than lectures.

I'm not a metalsmith or knifesmith of any sort, though I used knives professionally for 40 years or so. Even had a long stint teaching folks how to use them and how to sharpen them.

Just to add to the ramble, here's the best test for sharpness I've ever used. It's great for wet cold hands and lots of knives to go through in a very short time. You run out of hair on your arm pretty fast and your fingers are too numb to feel "sharp," light is too dim for close inspection, and paper turns back into its native pulp:

Very lightly rest the cutting edge on your thumbnail with the blade 90 degrees to the nail. Now try to slide the blade sideways in each direction. If it moves, it's dull. If it hangs up, it's sharp. You'll spot a rollover in an instant because it slides one way and hangs up the other. You can do that all along the blade and spot problem areas real accurately and go back to work on them.

I don't know if that's a standard test anywhere else, but it's the standard in the food processing industry. It's also dandy for cold, wet and dark on a hunt.

 

[ameling]

Yes, I've used that thumbnail test for years. Can't remember where I ever heard/learned it though.

And that level of "sharpness" really varies person to person.

Back when I was still in high school and living on the farm, I handed my pocket knife to my cousin to cut through a standard twine string on a hay bale. It took him three "pulls" to cut it. He then handed my knife back saying "gee that's SHARP" - and he meant it. I told him it was dull as a butter knife and really needed sharpening badly. He just couldn't understand that. I also decided at that moment that I didn't really want to ever borrow his pocket knife.

So "sharp" depends upon what the individual is used to. You really need to know their "scale" to judge things against.

I've also seen people at a "deer hunter's
gun/knife show pick up a razor-sharp custom knife, grip it tightly in their hand with the blade up, and run their thumb down along the edge to "...see how sharp it is"! The one guy said nothing, quickly put the knife down, and went walking down the aisle with his hand hanging down by his leg ... dripping ... as he walked over and into the restrooms. I got the impression that he thought all knives never got sharper than a butter knife.

And it seemed that most of the people walking through wanted a custom hand forged hunting knife for 30 bucks or less! One guy really really liked one nice hunting knife, saw the $300 price tag on it (which was kind of cheap for what it was), and literally threw the knife down on the table and stormed off down the aisle. (Luckily there was no damage to any of the knifes and sheathes on the table. Too many people are just too used to cheap China imports.

Mikey - that grumpy ol' German blacksmith out in the Hinterlands

 

[tg]

I started putting sharp edges of the replica NA blades for knives and lances I used to make from traps springs then quit and just put a light bit of an edge for looks because I got tired of the blood drops on my display table...

 

[grettadarlean]

How were you able to flaten the trap spring without heating it?

 

[BrownBear]

I put one half in the vise and pulled down on the other to get it started. Then I worked at it right on the bend on my anvil. Went pretty easy. The #0 is a pretty small trap, but I can't see it being all that much tougher on a bigger one. That'll be the next project.

BTW- Just got back from the range and trimmed another 30 patches at the muzzle on top of the 20 last session. It was getting pretty "iffy" for my tastes by the end. That puts it a little bit softer than the Russel Green River I've been using. Cool as it looks, I'm betting I end up throwing a little steel in the bag with it if I ever plan to use it seriously.

 

[tg]

You may find that some of the #3 and #4 springs may not bend as easy, I broke a couple trying a cold bend, some of the import traps had springs that would break occasionaly in cold weather but as Mike has stated if you have to heat them it is not a major task to temper to taste, I liked to pound both sides with a ball peen hammer and give a hammer forged/primitive look to them, makes a neat looking knife, show some pics when you get going on them.

 

[ameling]

How far you can bend/flex a trap spring to straighten it out without having it break varies greatly by trap manufacturer, and even the age of the trap. Some can be straightened out cold, but many will crack/break.

The "safe" way to straighten them out is to heat them up and then bend/hammer them straight and flat. But they you need to do the heat-treat again.

Since your small spring was "soft" enough to hand file to shape, it was already soft enough to flex/bend straight without snapping.

Plus, the smaller and thinner springs tend to have more "give" or flex in them than springs from bigger traps.

A bunch of those old original trap springs did break, and then were "re-used" for other things. The most common artifact found is a trap spring re-used as a hide scraper (or woodworking scraper). Since they often broke right in the bend, they already had the end curved down to work as a hide scraper. So all the Indians had to do was file/grind that broke end to shape, and sharpen it.

Just a few more humble rambling thoughts to share. Take them as such.

Mikey - yee ol' grumpy German blacksmith out in the Hinterlands

 

[BrownBear]

Thanks for the additional info on bigger traps Mike and TG!! Am I ever glad to have it before taking on the next step.

I've got a bud in town who's a custom knife maker with all the tools, forges and experience (he also lurks here and posts occasionally). I may see if he's got a little room to spare under his wing as I make the move to a larger trap, especially when it gets down to judgement calls on colors and such while tempering.

Once I replace the standard leather grip on this one with a rawhide version I'll try to go ahead and post pics.

On the aged look I made quite a score earlier this spring. We shovel and haul weathered seaweed for the garden. We'd spread a bunch on one of the potato patches and I saw this long black pointy thing stick up out of it. Turned out to be a standard Russell Green River boning knife that someone had lost some time back.

Talk about aged! The blade was rusty and scaling and the grip was eaten back in some spots. I used museum techniques to stabilize the handle and even left some scale on the blade while cleaning it up, then stabilizing. It now looks like some of the 18th century knives you see in museums and magazines. I took a file to the edge for a small bit of reshaping along with sharpening, but was careful not to stretch the bevel or scratch the patina on the rest of the blade, so it's serviceable now while looking a couple of hundred years old.

I'll try to post pics of that too. I doubt I'll ever find another while forking seaweed, but I'm betting I can bury a new one in seaweed in my yard for a few months or years and come up with the same look.