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The Newbies Arena Are you new to knife making? Here is all the help you will need.

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  #1  
Old 07-18-2010, 04:58 PM
DaveL DaveL is offline
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Work after heat treat, how to do it better

I use this forum because the answer may be here. After doing pretty good grinds. having cute little indention's and such getting heat treat scale off is a real chore for me. I do not want to destroy grind lines, do not want to alter shape and maybe as an old friend told me to heat treat before grinding on everything 1/8 or smaller. Ideas?
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  #2  
Old 07-18-2010, 05:25 PM
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Don Robinson Don Robinson is offline
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Dave, I grind the flats to size with a 220 grit belt before HT, then after HT I clean up the grinds with a 220 grit, then progress to 320 or 400, then hand sanding. After HT, the finish grinding doesn't really do much shaping, it mainly cleans the surface and refines the finish.

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Old 07-18-2010, 05:45 PM
Doug Lester Doug Lester is offline
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You can also soak the blade over night in white vinegar to eat away the fire scale. Also try to be sure that the forge is running rich so that there is a minimum of free O2 and CO2. That will reduce the scale. I find the keeping the forge temperature a low as I can and still get it hot enough to harden also helps a little in reducing the fire scale. Other than that, what Don said.

Doug Lester


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  #4  
Old 07-18-2010, 07:14 PM
Ed Tipton Ed Tipton is offline
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DaveL....There are two preferred approaches. The first is to control the heat to where it is a carburizing flame which will reduce the amount of scale that forms. The second is to use the white vinegar to soften any scale that does form. You neglected to mention what type of forge you are using, but if you're having a lot of scale my bet is you're using a coal forge. I use a propane forge, and by adjusting the flame carefully, I can almost totally eliminate any scale formation by running the mix too rich. I also try and grind nearly to finish grind before doing my HT. I have no proof, but the scale seems to not form as easily on smooth steel as it does on unground steel. These three techniques have reduced to problem of scale to the point where I seldom even think about it anymore.
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Old 07-18-2010, 07:24 PM
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Ray Rogers Ray Rogers is offline
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I grind after heat treat, always have. Using fresh belts I don't find it nuch more difficult to do than on annealed steel. Doesn't matter to me if the blade is under 1/8 or not though I may do a partial grind if it's really thick.

I started grinding after HT to avoid warpage problems and to reduce the exact issues you are struggling with. Now it doesn't matter if my blade has thick scale, deep pock marks, surface decarb, those weird worm lines or anything else. It all comes off when I grind the bevels........


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Old 07-18-2010, 08:29 PM
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J. Doyle J. Doyle is offline
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Quote:
Originally Posted by Ray Rogers View Post
I grind after heat treat, always have. Using fresh belts I don't find it nuch more difficult to do than on annealed steel. Doesn't matter to me if the blade is under 1/8 or not though I may do a partial grind if it's really thick.

I started grinding after HT to avoid warpage problems and to reduce the exact issues you are struggling with. Now it doesn't matter if my blade has thick scale, deep pock marks, surface decarb, those weird worm lines or anything else. It all comes off when I grind the bevels........
Ray, not to hijack this thread but does this process work on all steels? I've thought about doing this too but I use mostly 1080. I am currently under the impression that 1080 is a relatively shallow hardening steel and only hardens to about .100" as is. If that's true, 1/8" stock and thicker is out of the question. Just wondering your thoughts. Thanks.

John


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Old 07-19-2010, 09:22 AM
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Ray Rogers Ray Rogers is offline
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John,

I guess we'd have to do some testing on that to be sure but my gut feeling is that it would be fine. At worst, if you were making a 1/4" thick blade doing a rough grind first should solve the problem. I use a lot of 1080 and 1084 in damascus but that wouldn't show a problem with shallow hardening. I have made 1/9 and thicker blades from 1095 and ground them after HT without finding any problem .....


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Old 07-19-2010, 10:37 AM
Doug Lester Doug Lester is offline
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John, I think that you may be assuming that when you quench shallow hardening steel that you form a jacket of martensetic steel around a core of pearletic steel. That's not what happens according to Verhoeven's "Steel Metalurgy for the Non-metalurgist". Lets say that the shallow harding steel does only harden to 0.1" and the thickness of the blade that you are hardening is 0.25" thick at the spine. What will happen is that the steel will form martensite from the edge back to where the the blade is 0.2" thick. It will form pearlite where the blade is thicker than 0.2".

Also understand that the depth of hardening depends on the grain size with the smaller the grain the shallower the hardening. With a course grain, a shallow hardening steel could harden all the way through at 0.25" and with a very fine grain it might not be able to hold an edge. It's one of those ballance things that we keep running into in knifemaking.

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Old 07-19-2010, 11:40 AM
Jim T Jim T is offline
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Interesting... I was always taught to do most of the gringing prior to heat treating. The reason being that shaping of the blade is easier to do when the metal is still relatively soft (I use ATS-34).

Reading these threads, it makes sense to heat treat the profile and then grind, although I understand you might wear your belts down a little faster.

I'm curious to know, how far do other knifemakers take their blade grinding before heat treating?

Jim
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Old 07-19-2010, 12:12 PM
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Ray and Doug- thanks for the thoughts. I think that I might give it a try and see what happens.

Doug- good info. THat makes sense to me. Even if it hardens to .100", I didn't think about it hardening to that depth from both sides.

Jim, I've been taking my edges all the way down to .030"- .040" before HT and then thinning a bit with 220 grit after HT.


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Old 07-19-2010, 12:25 PM
DaveL DaveL is offline
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I sincerely appreciate all the reply s and there are some really good ideas here. Now I know I am trying the white vinegar for sure!
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  #12  
Old 07-19-2010, 12:35 PM
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Like most things in knife making, it's a matter of preference or convenience or simply what you get used to. I've done this on ATS-34 and S30V (much harder) and just about everything else we commonly used. Only 440V (of the steels I've tried) turned out to be more trouble than I wanted to handle, even D2 was easier. But, none of the carbon steels has been any trouble at all......


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Old 07-20-2010, 11:36 AM
CWKnifeman CWKnifeman is offline
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Most of the carbon steels can be done this way it is when you get into the high complex composition steels that this can be aproblem. I have tried it both ways, and have found that for the high composition steels that grinding prior to heat treatment is better in the long run. Grinding hardened high composition steel can really eat up the belts. Plus grinding some of the high composition steels will cause stress risers to form in the steel which might cause a failure somewhere down the line. S30V is one such steel which needs to be ground prior to heat treatment because of this. All steels are different and have different characteristics and as such have a different way in both heattreat and in grinding.
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Old 09-01-2010, 10:31 AM
Misfire Misfire is offline
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I've been terribly afraid of grinding after HT due to the risk of ruining the temper. It doesn't take but a few moments to get the blade too hot to touch.

How hot does the steel have to get to ruin the temper?

I mostly use 440C, D2 and ATS-34 though I have recently been playing with O1.

.
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  #15  
Old 09-01-2010, 11:26 AM
Kostoglotov Kostoglotov is offline
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Rule of thumb - If the blade discolors, you've messed up the tempering. Straw color comes about at 400F, brown/purble/bule at around 500F

Don't lean into your work, dip your blade early and often and use new belts.
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