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I Forge Iron

how do you test your knives?


Binesman

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My question goes out to the people who sell there work.  I have no intention of selling anything I make at the moment but I would like to give some knives to friends/family, without worrying that I'm giving them something subpar.  So how do you test your knives before you sell them to make sure they are/will remain sharp and true?

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A simple way to test for edge retention is by paper or cardboard cutting. Using a stack of paper, see how many times it can be sliced through before the blade gets noticeably dull. This is a little subjective but still a usable measurement.

The brass rod test, this is simply pressing the edge of the blade on angle against a brass rod and watching to see the edge flex and return to position after the pressure is released.  Be aware that not all metals will flex, some higher alloy steels will chip rather than flex in this test, even when performed correctly

Every so often, and every time a major change is made to the blade making process, a blade will need to be taken to its ultimate end. This is the death of every blade tested, why? It is the only way to know what it will take to fail. It is better to find out in the shop what a blade can do, and what makes it fail, than after its in the hand of an end user.  Obviously these tests are not done very often, they are selectively done, based on what is needed to be discovered. 

 

Chopping nails with a knife shows edge retention under abusive conditions. Use a mallet to drive the blade into the nail. A normal knife is not expected to be used this way, but hitting bone while cleaning game can be almost as destructive to the cutting edge. This is a test of that issue to the extreme.

 

Bending Giving the blade a 90 degree bend or some rotational twisting shows how the heat treat leaves the blade flexible while still having a good cutting edge. Once again under normal use this would never happen, but accidents can occur and people do abuse blades quite often. This shows how well a blade responds.  Remember to cover the blade with a section of pipe or an old welding glove to contain any flying pieces when it breaks.  Examine the pieces, look at how it broke and the grain exposed on the edges. That will reveal much about the heat treat.

 

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What Steve and Thomas said! 

If you are testing a new steel (or batch), supplier, or HT regimen it is a pretty good idea to do at least one test piece all the way to completion (within reason) and test to destruction as that will give you a MUCH better idea of where you stand. The crosssection you see when you snap a sample in the bend test will tell you for sure if you are getting huge grain growth.

Also worth investing in an HRC file set. It won’t let you get an exact number, but they give you a range and actually give you a really good idea when you are comparing between two objects (like testing two different quenchants or between your knife and a commercial one or a sample of a known hardness)

I really admire the testing techniques of Joe Calton and it includes a lot of what Steve covered, plus a lot of non destructive testing that can help you feel more confident sending something out.

Probably the best advice related to making sure you have something good going out the door is to use high quality stock from a reputable supplier and be familiar with what state it is in from the mill. It will remove a lot of guesswork and doubt. Looking forward to seeing what you make!

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I understand the different style knives being tested differently.  I was looking for answers across the board like for a chefs knife do this for a skinner this etc.

 

the stack of paper testing is a good idea.  As for hammering in to things I currently do that but with a piece of hard maple never thought about actually trying to damage the knife but it makes sense to push it to it's limits.  As for breaking steel and checking for grain growth.  I currently do this with fresh batch's of steel (not to a knife just a small 3" test piece) Is that good enough or should I forge out a full knife?

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If it is a new batch - especially something you haven't worked with before - I would do a coupon like you describe just to make sure nothing is off from the mill. Sometimes orders get mixed up so that will help you see if maybe something is way off.

After that to make sure there is nothing way off with your processes (in general), ideally you'd want to do everything to it you'd do in your normal workflow. The most straightforward test is to actually make a knife since that what you really want to test. Temperature is the bigger bad guy (vs time) with grain growth so if you really overheat it for just a short period, it can affect the grain. A cool experiment to help drive that home is to take an old file, snap it, and set it aside.  Then bring it to a yellow heat and soak it for like a minute. Then quench as normal and snap that sample. The difference you'll see between the two samples is pretty amazing. I can't find the original article, but I've attached a picture of what it looks like (not my picture - I'm sure this has been posted here a hundred times). We did this experiment at a buddy's shop one time and only let it soak for a minute at yellow, then air cooled it and brought it back up to around 1500 and quenched and it ended up pretty coarse. In sort, any high heats you have while forging can come back to haunt you later.

For the testing, it can also be very helpful to perform those same tests on a modestly priced commercial example of the same type you're making. You'll probably realize the bar isn't quite as high as you might be imagining ;)

EDIT: Realized that linking that image would violate some of the board rules. I'll try to find the photos I took of our experiment and post them here.

 

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Well, to compare cars with knives is often pretty compatible....if You drive the car against a wall and it is damaged , so it dosent mean it was a bad car.

IMHO It is the same with chopping nails(work of a cold chisel!)....a knife which can do this is simply dull, thick edged and not capable of cutting anything else than do coarse chopping.

or some "tactical"prying.

The same with bending....a big blade with 10inches by 4 mm thickness made of 1.2552 You wont be able bending it at all to 30 Degrees, the strength of this alloy is so solid and firm....it is possible but with a lever.

and beyond 40Degrees it will break like an explosion and You will stagger away from the vise, because of the amount of force compared to body balance.

But every maker has its testing, which is the free room of what every maker needs or believes.

Blades that are meant to cut should be tested with cutting.

Every new born blade I sharpen until it has got even burr.After removing the burr I take extra thin cigarette paper and I look at the cuts if there is tearing at the paper fibres.

It should be possible to cut fine stripes by stripe.You will see, where the burr is not removed completely...there the cut stops.

 I start with gently whittling a piece of giraffe bone.....examine with a magnifying glass the effects, followed by another cut in the paper to check

Followed by whittling ironwood and (sometimes) cutting card board...always checking the effect in the tore of the cigarette paper

after testing the blade still was hair popping, but has a bit tore on the paper.

Blade is made of O7, ground on the edge to 0,3 mm and has about 61HRC +/-1

Cutting bone and hard wood is IMHO much more telling in less time than cutting card board...because with some alloys  You need to cut a lot of card board until You can tell something about wear resistance.....too much time and card board messed all over the shop, You also need a temporary handle option to be able to make at least 100 cuts without hurting your hand

but again, knives are in a big range of what the maker expects and aim for.

 

 

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TWR8 n. Eiho.jpg

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8 hours ago, Gibson said:

Truth. (Gorgeous grinds, btw!)

......:)

I forgot to mention that the best testing(of course all IMHO) is, to carry and use the blade for an amount of time.Of course it is not possible for a full time maker to do this with every blade, the same with testing abrasion resistance on cutting cardboard.

so it reduces it to testing  the stability of a fine edge which is to me actually more important than testing wear resistance....like for example: it is technically obvious that O7 is more abrasive resistant than 1095 ....how is that said in English?....we can tell it i/fromn the books?

I had over the years now and then a blade which I was not satisfied with the grind and sorted it out.Such blades remain on the bench and being used and abused for all the dirty work I wont use a blade normally....and I was often amazed what these knife blades could and did endure.

Cheers

 

8 hours ago, templehound said:

 

 

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It can be a big help to identify a "blade tester" for you; exp: if you plan to do a lot of camping/hunting blades; make friends with a good outfitter/guide and discuss what they want a blade to do and then send blades into the wild with them and debrief on what could be improved on a regular basis. This also has the pluss that folks with enough money to hire such people get to see YOUR blade(s) in use and perhaps decide thay gotta get one like that!

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templehound.  Thankyou that was exactly the kind of info I was looking for.  I understand it's all up to me in the end but I'll be honest I have no idea where to start.  What you gave me is an excellent example of what you do for a certain blade type/style/size to give me ideas going forward.  

 

Thankyou to everyone else who has responded all the info has been very informative.

 

Thomas.  That's kind of my plan with making knives for friends/family.  A lot of them hunt and I want to send them with knives for feedback.  However I don't want to send them with a steaming pile of scale disguised as a knife.   ;)

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usually I make a couple runs of a batch of steel making them into knives, and then smash blade edge on blade against a steel I know and have frequently used before at "cuts a paper without trying". might also plane some wood with the blade and see how long the edge lasts, typically record my primitive tests in a log book.

hammering a blade though something like stock while its touching is waaaaay different then cutting through something and hitting a part of metal at speed, the best thing I can think of to get an idea of damage is another hardened blade. Mind you this is a swordsmith perspective, and I might make a blade to suit a factory or fabrication needs where its being compared to a disposable razor instead for slicing aluminum or cutting open boxes and thread straps ect.

this gives me an idea based around how I am doing things about what to change or seems ideal to make the blade last longer.

Then of coarse there's the typical ABS tests like sawing through rope ect.

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There is a knife test mentioned in "Consider the Fork; A History of How We Cook and Eat"   (not much academic rigor in it's "history" sorry to say. It's my current "non-fiction" book; just finished re-reading "The Stars My Destination" a SF classic.)

"There's a joke about a man who tested his blade using his tongue: sharp blades taste like metal; really sharp blades taste like blood."

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I've worked in several kitchens around the city where I live, so I luckily have a large group of people eager and willing to test my work. I usually leave them for a week or two and ask that they don't hone or strop at all.  This also has the helpful side effect of advertising my work and nabbing a sale or two.

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