Brass rod test, off angle?

N.W. Gean

N.W. Gean

Joined
Oct 10, 2018
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463
Good morning all. I've been testing a lot of my blades lately on a 1/4" brass rod but have found my forge HT to be unsatisfactory. The edge bends a little and stays bent, but not nearly as much an unhardened blank would (I've done it for comparison). What I realized a few minutes ago was that I've been going way off angle and using a lot of pressure to make this happen. When I matched the sharpening angle, it took an even greater amount of pressure to cause any deflection, and it seems like it springs back (maybe some tiny rolls remain).

Maybe I've answered my own question here, but am I asking too much of my knives or conducting the test improperly? Realistically, is going too far off angle always going to destroy the edge regardless of HT quality?
 
When the edge deforms and returns to straight means you are using the correct pressure. If you move the edge too far and exceed the elastic limit, it will not return to straight. This rod test works on steels with different hardnesses, so use a Rockwell tester for hardness checking.
 
Without seeing you attempt the brass rod test it is impossible to determine what is happening.
So, if you have an old knife which performs well, try doing the test on it to see what it looks like. I suggest 5 to 10 degree angle above grind angle.
I suspect if you search YouTube you can find a tutorial.
Jim A.
 
tkroenlein said:
Don't put too much faith in the brass rod test.
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Could I have a good heat treat and still fail the test? I can't afford a rockwell tester so I'm trying my best to see if my knives are good. Some bend on the rod and some don't, they all skate a file to varying degrees, and I'm left with hearsay and conjecture :D

Funny enough, Jim, I was also able to make a mora knife roll. I think I don't know how to do the test right :)
 
It's easier to test flex and return using a 1 inch or so brass or copper pipe...easy to overdo it with the small rod.
 
Whether or not you are "doing the test right" is highly subjective, because there is no standard. It may, with enough practice, allow someone to gauge their own work against themselves. You will mostly be measuring the thickness of the edge. I suppose if you totally blow a heat treat by over heating it might chip out. But rolling is caused by two things too thin or too soft for the task that was being performed. Just my opinion. I know others trust this test. But I personally find no value in it.
 
I think there is some validity to the test, but it's certainly not the be-all, end-all of testing.
I mean when it comes down to it, the real test is how it actually performs at the task it was designed to do.
I mean if you have a knife designed to cut jello, it doesn't exactly need to be super sharp, or have a super high toughness edge does it?
It's just another metric in your testing scheme, right next to RC hardness, bend testing, destructive testing etc...
 
rc tester only tests at the ricasso, there can still be differences on your edge. no matter how or what angle you are pressing, it should spring back all the way. i think your metal is too soft. what is your heat treat like ? type of steel?
 
john april said:
rc tester only tests at the ricasso, there can still be differences on your edge. no matter how or what angle you are pressing, it should spring back all the way. i think your metal is too soft. what is your heat treat like ? type of steel?
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Forge HT. It has a thermocouple but I think it reads atleast 100 degrees too hot, because a magnet was still attracting the blade while the PID read 1500. 1075 steel.
 
So I have a new piece to add to this puzzle. I tried redoing the heat treat in my forge, the thermocouple reading 1500 +-20, the knife not sticking to a magnet, melting table salt dropped on the knife (it sizzled as soon as it hit the knife but only melted inside the forge), and it looks like the knife was overheated. The grain looks sandy and there is blistering on the side. I didn't normalize so it was likely trashed before, but I think I'm having a really hard time telling when it should be quenched. I know I definitely had it in the forge too long, but if it really was 1500 would the damage be this bad? Or is it safe to conclude the thermocouple is behind?

GrainStructure.jpg Blistering.jpg
 
you are not giving enough details of the heat treat to give a guess at a diagnosis. what is the fuel in your forge ? what is your quench ? what temp is your quench when you stick the knife in ? if the magnet is still sticking to the knife, it was not hot enough to quench. that is probably why your metal did not spring back. heat your metal to non magnetic, note the color red and remember it, heat the blade one shade brighter red before quenching. proper temp is about 100 degrees higher then non magnetic.
 
Propane. Canola oil. ~120 degrees. Magnet wasn't sticking this time. I'm thinking that the knife wasn't up to temp yet the other day. Salt was melting on knife (suggesting at least 1474?). I'm scratching my head on this one. Call it inexperience.
 
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I might have missed it, and I know you're heat treating in a forge, but was this a forged knife, or stock removal? Did you normalize at all? How large is your forge and where is your TC located vs where you're heating the blade? Are you moving the blade while it's heating? Is touching the flame/burner at all? How's your fuel/air mix? You want more of a reducing atmosphere (fuel rich) vs oxidizing (air rich).

You might try using the pipe method for heat treating in your forge. Get some sch80 pipe a little larger in diameter than your blade is wide, and let it come to temp in your forge. Some guys put in a little bit of charcoal or some other consumable to help reduce oxygen further. Either way, the pipe should help even out any hot spots that might be overheating your blade.
 
Your 1075 may not be hardening in the canola oil. It's marginal under ideal conditions. Without precise heat control or a good bit of experience forge HT'ing, you could very well get hit and miss results.
 
Drew Riley said:
forged knife, or stock removal? Stock removal.
Did you normalize at all? Not this time, but I did before. I tried to soak each cycle at 10 minutes and that was probably too much.

How large is your forge and where is your TC located vs where you're heating the blade?
16" L x 5" mouth. Dual outlet blown burner. I have the thermocouple sitting in a pipe muffle that has standoffs so the flame can swirl. The thermocouple is roughly between the 2 outlets.

Are you moving the blade while it's heating?
Trying to.

Is touching the flame/burner at all?
No.

How's your fuel/air mix? You want more of a reducing atmosphere (fuel rich) vs oxidizing (air rich).
Undetermined. I'm not sure how to check other than the fact that the blower is set halfway and the gas pressure is about 1/2 to 1 PSI to have the PID reading ~1500.

Some guys put in a little bit of charcoal or some other consumable to help reduce oxygen further.
Good idea. I've heard a shot of WD40 in the muffle might also work. Good or bad idea?
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tkroenlein, I was thinking about that at work earlier. I have a local source of Parks 50. I think I'll be picking some up in the morning.

Thanks for all the replies everyone. I appreciate your time.
 
Well I'm afraid I've hit a snag here. First, the local store is out of parks 50.

Second, the forge has a massive hot spot. I was pumping the blade like crazy, but the tip was still shooting past non magnetic and the edge at the ricasso was still sticking to the magnet. I even flipped around and heated the tang, but no dice. I was using the muffle so it's as even as it could get, right? Still, I don't want to blame anyone but myself because I really think there's something I'm not understanding.
 
So one thing I do while using my smaller forge (it's more erratic on maintaining temps) is I'll hold the knife across the opening of the opening to heat the main body of the knife.
That way I can get everything heated up pretty hot before I stick the whole thing to get it up to final heat. Just trying not to over heat the tip!!
 
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