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When or how often do I need to replace my quench oil?


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If it stops fully hardening your steel and you haven't changed your process, it's time to change it,  if you're using canola or mineral oil.

If you're using a real quench oil, they make rejuvenation packs for when those slow down. 

But anyway, if you notice it's just not working like it used to, something needs doing.  

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Every three months or 3000 miles... No, seriously how do you know if it's your oil that's not fully hardening your steel or some other variable? About how many quenches can you get out of a bottle of canola oil?  

 

 

On 1/11/2022 at 6:04 PM, Alan Longmire said:

If it stops fully hardening your steel and you haven't changed your process, it's time to change it, 

 

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This may not be the most scientific method, but here's what I do.

My quench oil tank is an 8" x 8" x 27" square tube. 5 gallons will fill this to within 4 inches of the top.

 

Quench tank.JPG

 

Now quench oil burns off over time. So when it got down to  about 12 inches deep, I replaced it. Took about 15 years to do that.

I use Parks 50

 

 

 

 

Edited by Joshua States
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16 hours ago, Steve Gilligan said:

No, seriously how do you know if it's your oil that's not fully hardening your steel or some other variable?

 

That is the trick, isn't it? :lol:  If your process hasn't changed, but you notice your blades aren't performing the way they used to, the oil is a major variable to check IF you're using canola.  Over time it does break down from the heat, and gets slower.  It usually goes rancid before it slows too much, so when it starts stinking instead of smelling like fry oil, it's time to change it.  Or if a mouse drowns in it.  Believe me, you'll know the first time you quench in it that something is horribly wrong.  The smell is indescribably noxious. 

 

If you're like most home shop makers, you'll be quenching no more than five or ten blades a week maximum, often one after another in one day, then letting the oil sit for a weeks or months until you have another batch ready to harden.  If it goes rancid, you'll smell it with the first quench.  

 

If you're using a commercial oil like Joshua's Parks 50, as he said, you lose more to drag-out than to getting too used.  Commercial oils (and straight mineral oil) last for years in the average home shop environment.  Only if you're quenching so many blades per day that you need an oil cooler and circulating pump to keep it in the spec temperature range do you need to worry about it breaking down. And I don't know any makers, even full-time professionals, who need that.  Industry, yes.  One-man shops, not so much.

 

Finally, one of the many reasons not to use motor oil as quench oil:  over time it absorbs water from the air, which results in increasingly fast and uneven quenches.  It's designed to do that, and in your engine that's a good thing.  In your quench tank it isn't. 

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9 hours ago, Alan Longmire said:

you'll be quenching no more than five or ten blades a week maximum, often one after another in one day,

I once brought this up to a young maker when he was trying to figure out what went wrong with his quenching. Yeah, he did 5 or 6 knives right after one another in a gallon can filled with canola oil. He couldn't understand why they came out with different hardnesses.

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I used to have a big quench tank but that turned into a bit of a mess, so recently I've been using smaller containers.

Canola oil exclusively, I monitor and keep it around 60C by adding more oil if it gets too hot after a few quenches etc etc.

Because I pour the oil back into the containers after it's cooled down I can judge the state of the oil, canola gets darker and the oil in my original tank was most likely rotten. 

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my quech tank is 6 inches in dia and holds over 4 gallons. I often have numerous knives to do at one time but have a perforated  scoop in the tank just a bit smaller in dia with long handle that reaches the rim and was originally intended to scoop out anything that fell in the tank but I use it more to stir the oil bottom to top to ensure there is a uniformity of temp throughout the tank for when multiple blades are quenched.

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On 1/13/2022 at 9:25 PM, Joshua States said:

I once brought this up to a young maker when he was trying to figure out what went wrong with his quenching. Yeah, he did 5 or 6 knives right after one another in a gallon can filled with canola oil. He couldn't understand why they came out with different hardnesses.

 

Yeah, that needs to be taken into account.

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