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Post by Matt993f.o.d on Jan 16, 2008 21:36:45 GMT
In my reading I have come across several ways of tempering knife blades. I don't really know how effective each one would be. Can you guys tell me which of the following results in the best temper?
The first is torch tempering; polishing the blackness of your blade after normalizing, then holding a bog standard blowtorch on the spine of the blade and drawing it back and forth, watching the colour of the oxide film run across the blade, stopping when the edge gets to purple. This sounds a bit temperamental, and half assed to me though.
The second is "sand box tempering". Apparently done by covering your whole blade in a thin covering of sand in a aluminium box, then heating the underside of the box with a blowtorch. The blade is dug out once it reaches the correct colour of oxide film. God knows how you know when to take it out!
The third is a variation on torch tempering, but a little more refined. Used by African smiths, who have little access to more advanced equipment, their method of choice is to heat a large flat-faced brick of iron in the forge to red or orange heat, then to place the spine of the blade onto the iron, and watch the oxide film move as with torch tempering. This is superior to torch tempering in theory, as the blade (if the whole spine is in contact with the block of iron) is tempered a lot more uniformly.
The last method is simply to place the heat treated blade in the oven. The thing that I don't get about this one, however, is that if you are using unknown steel types (if you are making knife blades from old leaf springs, say), you cannot be sure how long to temper for, or at what heat. It is also more difficult to check the progress of the oxide film.
Am I talking semprini here, or do any of these methods have some substance behind them?
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Post by themaster293 on Jan 16, 2008 22:34:50 GMT
All I know is that if you leave steel in an oven at 600 degrees for four hours is gets a spring temper. Sorry I could not be of more help.
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Post by Deleted on Jan 17, 2008 1:19:05 GMT
In my reading I have come across several ways of tempering knife blades. I don't really know how effective each one would be. Can you guys tell me which of the following results in the best temper? The first is torch tempering; polishing the blackness of your blade after normalizing, then holding a bog standard blowtorch on the spine of the blade and drawing it back and forth, watching the colour of the oxide film run across the blade, stopping when the edge gets to purple. This sounds a bit temperamental, and half assed to me though. It is accepted and OK to do this, but tricky. PROPER tempering is done over hours not seconds or minutes. The second is "sand box tempering". Apparently done by covering your whole blade in a thin covering of sand in a aluminium box, then heating the underside of the box with a blowtorch. The blade is dug out once it reaches the correct colour of oxide film. God knows how you know when to take it out! It is heating a steel box full of sand with the part suspended in the middle of the sand, the sand evens out the heat and makes for no hot spots. It can be done over a coal forge fire, charcoal or with a torch. The third is a variation on torch tempering, but a little more refined. Used by African smiths, who have little access to more advanced equipment, their method of choice is to heat a large flat-faced brick of iron in the forge to red or orange heat, then to place the spine of the blade onto the iron, and watch the oxide film move as with torch tempering. This is superior to torch tempering in theory, as the blade (if the whole spine is in contact with the block of iron) is tempered a lot more uniformly. basically the same as torch tempering, and sand tempering, all three involve "running the colors", insufficient tempering practices. The last method is simply to place the heat treated blade in the oven. The thing that I don't get about this one, however, is that if you are using unknown steel types (if you are making knife blades from old leaf springs, say), you cannot be sure how long to temper for, or at what heat. It is also more difficult to check the progress of the oxide film. Most basic steels can be tempered very similarly, in fact almost identically. What you use for your temper depends on your own personal expeirience as you grow as a maker, and your personal understanding of the steels you work with. Am I talking sh*t here, or do any of these methods have some substance behind them? All these methods except for the oven one are basically the same. Proper tempering as i said already happens over hours, not minutes to run the colors.
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Post by Matt993f.o.d on Jan 17, 2008 9:00:38 GMT
Cheers Sam! The oven seems to be the way to go. People have come up with all sorts of ways of doing it. One fellow on IFI tempered in an oven for 2 hours, then ran the colours with a red hot brick afterwards. Seems like overkill to me.
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Post by Dan Davis on Jan 17, 2008 14:37:23 GMT
Matt, As we said in the quenching thread:
None of those methods allow for enough time to temper EXCEPT the last one. I'm completely onboard with Sam on this one.
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Post by Matt993f.o.d on Jan 17, 2008 16:06:27 GMT
Cheers guys. If you were to sit your blades in the oven to temper, do you do simply that? Or do you put them on something, to allow the heat to reach them uniformly?
I was thinking, would it perhaps be a good idea to put the blade in a sandbox, before tempering in the oven? I reckon the heat could reach the blade a bit more evenly than if it were sitting, say, on a rack or metal tray.
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Post by Deleted on Jan 17, 2008 16:17:20 GMT
Cheers guys. If you were to sit your blades in the oven to temper, do you do simply that? Or do you put them on something, to allow the heat to reach them uniformly? I was thinking, would it perhaps be a good idea to put the blade in a sandbox, before tempering in the oven? I reckon the heat could reach the blade a bit more evenly than if it were sitting, say, on a rack or metal tray. No need for the sandbox in the oven, your wife would kill you anyway. Just set it in on the grate, the hot air circulates enough to heat it evenly. Yes just set the temperature and stick them in and LEAVE them alone for 2 hours.
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Post by Matt993f.o.d on Jan 17, 2008 16:22:08 GMT
Ah well, I thought it sounded a clever idea at the time I've got another question whilst I'm at it (to save me starting another thread). What is your personal experience with brine quenching. It seems the jury is out as to whether it cools the steel faster or slower than water. No one can agree! What is your personal experience with it?
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Post by Deleted on Jan 17, 2008 18:01:20 GMT
It is scientifically faster, it has been proven.
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Post by Matt993f.o.d on Jan 17, 2008 20:09:06 GMT
Oh dear. When would you possibly need to cool a blade faster than water can?!
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Post by Deleted on Jan 17, 2008 20:17:08 GMT
Because sometimes it is needed, sometimes it is impossible. Water is actually a crappy quenchant. The salt in the brine actually makes water cool more evenly, as as the vapor jacket forms around the peice when you go into the brine, the salt will boil out and go onto the steel, which gives the water something to grab onto which reduces the vapor jacket effect, meaning faster cooling through the most critical range.
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Post by oos3thoo on Jan 17, 2008 22:06:11 GMT
Whats Brine?
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slav
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Post by slav on Jan 17, 2008 22:30:28 GMT
Saltwater, basically.
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Post by Deleted on Jan 17, 2008 22:57:52 GMT
Not just saltwater, proper brine is 10% salt to water ratio, adding more salt will not do anything better. There was that old japanese saying "enough salt to float an egg".
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Post by oos3thoo on Jan 17, 2008 22:59:38 GMT
Does anyone know the difficulty on making a sword out of a tempered bar of steel? I mean, already pre-tempered and and hard? I may just do that, seems easier.
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Post by Deleted on Jan 17, 2008 23:08:11 GMT
Does anyone know the difficulty on making a sword out of a tempered bar of steel? I mean, already pre-tempered and and hard? I may just do that, seems easier. it is very hard, the steel is very tough and abrasion resistant, and you have to be very careful to not remove the temper on the steel already. Look to spend 10 times as much time doing so as you would if you were to start with annealed stock and then HT it yourself or send it out. IT IS NOT EASIER.
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Post by oos3thoo on Jan 17, 2008 23:11:05 GMT
Well, all the tools I got are a file, a hacksaw and hopefully a grinder!
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Post by Deleted on Jan 17, 2008 23:35:18 GMT
You would be at it for weeks then! Hacksaws will not touch well heat treated steel, barely even spring tempered steel, files will not do much either and you will have to be very careful with the grinder.
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Post by oos3thoo on Jan 18, 2008 4:11:12 GMT
Well what can I do? I need suggestions for people like me who do not have a local forge!! D:
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slav
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Post by slav on Jan 18, 2008 4:27:17 GMT
Start out making knives. Lots of them:
Buy annealed high-carbon bar-stock from Admiral. Shape it with files, grinder, etc via stock removal. Heat the blade up red-hot in a hot fire a few times to normalize it (build a good bonfire, or I have even used my fireplace). Then quench it. Then temper it in the oven or over the fire.
Look around on the net for detailed information and better instructions. Study them for days and days. Then try your first...second...third...fifteenth... After perfecting your technique and producing about 20-30* perfect knives, then consider making the next step to forging swords.
*Results and failed/successful attempts will vary. For more information contact your nearest Sam Salvati.
'bout right Sam?
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