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First farriers rasp knife


Bad_Rockk

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Hello,

I'm currently making my first knife. For the stock I used an old farriers rasp. 

I first annealed the rasp and then quenched the tang and break it to see if it's worth using the material for a blade. It broke easily. So I will heat treat it like 1090/1095.

here a picture to get the size of the knife (40x165 mm / 1.5 x 6.5 inch, 4,5mm/0,177 inch thick). The shape is inspired from the "Chunky Monkey" shape of YT Simple Little Life. I want to use the knife for cooking. 

IMG_20201201_160608.thumb.jpg.13a89f151b279f8862563897c6fe0caa.jpg  IMG_20201215_142112.thumb.jpg.9cade75b0a1e48c86c3834425ba5a425.jpg

The rough shape I did with an angle grinder and a 3x21 belt grinder. I did the bevels with a hand file and a jig. I removed the deep scratches with an orbital sander (80 grit) and then handsandend with 120/220 grit. Unfortunately I now already have a pretty sharp edge before heat treating. 

The handle will be made of Padouk with 6mm stainless steel pins.

So my question is, can I heat threat the knife with the sharp edge or do I have to increase the edge width by removing more material? 

Greetings from Germany,

Tim

 

 

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Hey Tim, you'll probably want to increase the thickness of the edge by removing some of the width prior to heat treatment. I usually leave the edge around 2mm sometimes down to 1mm thick going into heat treatment. However, 1mm is pretty thin in my opinion. Now that's probably more width than you're looking to give up on your overall profile, so that's more for future reference.

After removing some material, when heating your steel up for heat treatment, you'll want to heat very slowly, keeping in mind that the thin areas will heat up much faster than the thick spine. You want to avoid overheating the edge which will both increase the grain size and cause unnecessary decarburization, thus lowering the quality of your edge. Once everything is heated up evenly, you'll be good to go. 

I have quenched a knife that was brought back from being sharp and it can be done. No matter what it's not going to be ideal, but it can be done. 

P.s. I like the knife, what are you thinking for handle scales?

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Hi Frazer,

Thank you for sharing your experience. Yes if I would increase the edge to 2 mm a lot of the blade profile would be gone. So I will try it with 1 mm and try to heat up the blade slowly. 

For the next knife I will pay more attention to keeping the edge thick enough. Also I will buy larger material to make the blade around 50 mm / 2 inches high.

For the scales I have some african padouk (barwood) with nice redish colour. 

Is handsanding to 220 grit fine enough before heat treat? I'm not going for a mirror finish. 

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Since you did stock removal rather than forging, this doesn't apply as much, but the best blades are generally forged thick then ground thin. Mostly to limit decarburization  that is inherent to the forging process, but that can come as a result of overheating while hardening I suppose. Only to a much lesser extent.

220 is plenty, in my opinion. If you took all the time to go to a mirrored finish it would be ruined by the quench I don't make may knives but when I do I finish the profile, start my plunge grinds and drill the holes after annealing. Then finish all my grinding and hand sanding after the blade has been hardened and tempered.  

If my first knife looked half as nice as that one I would have been very pleased. Looking forward to seeing it complete.

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Hi,

yesterday I did the heat treatment of the blade. 

I did not increased the edge to 1 mm because I would lose about 5 mm of blade hight. During hardening I realised that the thin material is also problematic because it not only heats up faster but also cools faster. It's not ideal but for knife #1 I can live with that.

I heated to non magnetic and quenched in canola oil (60°C / 140 F). But the file test wasn't as expected. The file did leafe some scratches on the blade. But I'm not sure if it was just the burned oil on the blade. 

For tempering I aimed for 2 X 60 min at 220°C / 425 F. The first hour went well and I got a light straw colour. I let it cool the room temperature and went for the second hour. I didn't watched after the blade and went for a shower. And the tempering failed:

IMG_20201217_170808.thumb.jpg.51ede9bb6a686df2d3a65770e37091ac.jpg

According to the colour on the edge the temperature was around 280-300 °C / 530-570 F. 

So my plan is to redo the hardening and tempering. And this time observe the tempering and working with lower temperature.

Question:

is the hardening correctly only if a file doesn't remove any material / make any scratches? Or do I have to remove the black "skin" (what is the correct wording for it?) befor the file test?

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But it's not a second tempering cycle it's a second Hardening and Tempering cycle and does not need any time between.

Scratches may indicate that there is a decarb layer that will be removed with final grinding/polishing.

425 degF may be a bit high; I'd try 350 degF first and work your way higher if you decides it needs it.  500 degF is getting into the blue range!

Also if you are using a kitchen oven to temper in remember that their "set" temperature is NOT what is actually in there as it will cycle up and down around it and where it is in the oven affects the temperature too. (Oven temperature gauges are notoriously inaccurate.  Getting an oven thermometer can help.)

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Hi Thomas,

Thank you for your recommendation.

Yes, I will do a new hardening and tempering cycle with 175°C/350F. I understood Pnuts post that I should do the 2x60 min tempering with 1 day in between.

I will put a BBQ thermometer in the oven the next time. I knew that ovens aren't that precise but I didn't expect deviation of 60-80 K. This is almost 50% off. 

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OK. So here's my 2 cents. DONT DO ANOTHER HEAT TREAT CYCLE.  Just yet.. What does a file  test of the edge tell you. Clean up the edge. grind it and sand it than run a good file over it.. If as suggested it, 1095 steel, a 425 temper could have a Rockwell hardness of above 60. If a file will have a hard time cutting that. 

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I knew this was going to happen. As I understand it the maker used an oven to temper this blade.  Blades tempered  in electric ovens will exhibit such color patterns.  Oxidation,oils, and alloys are players. If he did another temper cycle the colors would get even darker. Unless his stove/oven is wildly  out if wack its not possible for the knife to get enough to get hot enough to get the 525 deg plus temperature to produce that coloring. 

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I guess I did make some assumptions after rereading he did not specifically mention the specific  device or technique use to temper. I just tried to say dont jump the gun by assuming the colors. If he's using a flame drawback technique then as mr. Powers pointed out he's got the technique  backwards. Of he's using a temperature controlled device then I say its way off. Approximately 100 deg F. using his numbers and the edge colors. 

BAD Rock. As an aside. I used an electric kitchen stove to do my first knife shaped objects. Yours is way, way, better.  I had similar color results and assumed I messed up. Several tests later I found out that colors can be a guide line but sometimes don't tell the whole picture. As I said earlier.  Oils, alloys  and oxidation contribute to colors when done in enclosed ovens. My first blades tested between 58 and sixty 6sing Rockwell hardness files. Do some tests first.

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17 hours ago, ThomasPowers said:

But it's not a second tempering cycle it's a second Hardening and Tempering cycle and does not need any time between

I was asking if waiting a day before a second tempering cycle to let any retrained austenite convert to martensite as a general good practice whenever tempering a knife versus tempering in an oven, letting it cool to room temperature and immediately putting it back in the oven for a second tempering cycle as it sounds like the op did. From what the op typed there was no mention of waiting between the two tempering cycles.

Pnut

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Addressing temperature errors with kitchen ovens.  We have a GE electric convection oven with electronic controls.  I would hope the convection part would help alleviate any hot spots or uneven heating.  That being said, I had a couple of pieces that I tempered according to the oven settings and they came out a bit too hot.  I got an oven thermometer and checked the settings...the oven was about 30-35* too hot.  No wonder my biscuits were cooking too fast and nearly burned!

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PNUT. since no one is responding I thought I'd take a shot. Mind, I'm not a metallurgist. I would think that when the blade is removed from the heat source any transformation of austensite to martensite would stop.  Nothing in my research suggests that the transformation continues after removal from heat source.  If anyone has documentation that it does I'd appreciate  being pointed in that direction.. 

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The transformation isn't dependent on being in the heat source, it depends on how long the blade is within the transformation temp range. 

A thermometer in the oven is a must, the appliance thermostats and temp gauges have pretty wide tolerances. Or electric convection oven is within about 30+ the set temp according to the oven thermometer. 

And that's about what I know about tempering, not a lot but I do know a little about kitchen ovens.

Here's a tidbit for you, my shop toaster oven, $5 at a church rummage sale, is more accurate than the kitchen oven. I think that's because it's small so oscillates between the high and low limits quickly and so maintains a more constant temp.

Frosty The Lucky.

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