Can you heat treat small parts at home?

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RSG
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Can you heat treat small parts at home?

Post by RSG »

I asked a question earlier regarding rockwell hardness of a few different stainless steels and in my quest have decided that 420 is the best for my application.....(I think). From what I have learned it's annealed state is still harder than 303 but has the capability to be hardened should I want.

With that said I got a bar of it the other day and chucked it in the lathe and it machines fine, but with very wirey swarf. It's stated that it's optimal hardness is achieved at 900 - 1035c and oil quenched. Would it be reasonable to assume I could achieve this using a map gas torch and checking the temp as I go? I have a very good quality IR temperature gun that I will use.

Any input would be appreciated.
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liveaboard
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Re: Can you heat treat small parts at home?

Post by liveaboard »

I do.
I use a torch sometimes, other times an electric kiln.
The torch works better, because it's very fast and there's little or no oxygen during heating. Work in the kiln oxidizes on the surface during heating.

I bought some drawn rod and I don't know what it is (lost the receipt). But after treating it gets so hard that a carbide lathe insert bounces off.
Tempering in the oven at 500C makes it a little more malleable.

I just heat it up like this, then drop it into a bucket of water.
ruhla 250-710 quill handle hardening rod.jpg
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slightly higher tech; OH is a ceramicist
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Harold_V
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Re: Can you heat treat small parts at home?

Post by Harold_V »

Assuming you'll treat reasonably small parts, a burnout oven (typically used for investment casting) can be used for heat treat, and you'd have some control over soak time and temperature.

Heat treating isn't hard to do, but proper heat treating does require some degree of control. Professional ovens often have tight control of temperature---as close as ± 1°.

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pete
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Re: Can you heat treat small parts at home?

Post by pete »

How big are the parts and how many will you be doing Ron? The parts mass will dictate if you can get it hot enough and fast enough with a hand held Map Gas Torch. Clickspring's videos on Youtube are probably about the best I can think of since he does a lot of tool making and hardening. He uses simple Boric Acid so the part doesn't scale, and it might help a bit with decarburization. He says he gets that from Roach bait at the hardware store, but he's in Australia, I've no idea if ours is the same, but any pharmacist should be able to tell you where to find Boric Acid. Clickspring mixes it with denatured alcohol and applies it as a paste, it washes off after heat treatment with boiling water or in the quench. For where it comes from in his case, it's not something I'd use to heat treat anything indoors though. :-) For this video, the Boric Acid application and heat treatment starts at the 6:21 minute mark. https://www.youtube.com/watch?v=MYI1slVGziU While it doesn't deal specifically with heat treating that SS alloy, given it's cost I highly recommend this book and from the same place in the link. https://www.teepublishing.co.uk/books/i ... treatment/ The Ebay re-sellers all want far more for the exact same thing. It's good enough I spotted a copy on the book shelf at a commercial heat treating company I was at. To be fair they had a few hundred way more expensive one's as well.

I think it's helpful to understand the complex changes a part goes through as it's being hardened and then tempered back down to the general properties your wanting. But you also asked for input. Are these going to be parts for your reels? Because there's also heat treatable titanium. Fwiw, one I've machined is Ti-6AI-4V. Not the greatest to turn for the best surface finish, but doable with standard carbide or even HSS for drilling. If you do go in that direction it's even worse than 304 SS for work hardening. You have to keep any tool generated heat out of it prior to heat treating it. Very sharp tools, lower rpm, higher feed rates, and in a home shop lighter cuts with at least brushed on coolant would be a good idea. And it's probably not that hard to find around your area. I'd also clean out the lathes chip pan and not let a whole lot of that Titanium swarf build up. It's not impossible to have it ignite if you get unlucky and have an area of swarf get hot enough. It's not happened to me (yet), so you just need to be a little careful. I'm a bit paranoid about Titanium, so I keep a pair of pliers and leather gloves handy as well as an empty steel container to drop it in if there was ever an issue. Water and even fire extinguishers won't put a Titanium fire out. Enough sand to fully cover it will, but I'm not dumping sand on any of my machine tools.
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Re: Can you heat treat small parts at home?

Post by Glenn Brooks »

According to the guy at our local hardware store, youncan’t get real Map Gas in the US anymore - the formula was changed a year or two ago, and replaced with a lower BTU product. Hence now, no better than propane.

However, you could build a simple propane fired forge, or fire brick oven, and easily get red hot heat with a 5 gal propane tank and a weed burner. I build a backyard foundry couple of years ago with insulating wool and half a 20 gallon chain barrel. Worked well enuf to sweat a bunch of 8” cast iron RR wheels onto shafts... with an IR gun you can at least know temps you are dealing with...

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Re: Can you heat treat small parts at home?

Post by choprboy »

Glenn Brooks wrote: Sat Nov 20, 2021 7:22 pm According to the guy at our local hardware store, youncan’t get real Map Gas in the US anymore - the formula was changed a year or two ago, and replaced with a lower BTU product. Hence now, no better than propane.
Not quite true... real MAPP gas is a mix of propyne (methyl-acetylene) and propane. You would have to get it from a gas supplier though, it isn't available in general stores any longer. What is available is "MAP" gas, which is propylene (propene) and propane. Propylene is the raw feedstock gas used to make polypropylene plastics.

MAP gas most definitely puts out more BTUs than straight propane. I have both in my toolbox, if I want to pre-heat something or solder something small I use the propane. But if I am soldering 3/4"+ copper pipe or want to heat a bolt up cherry red, I grab the MAP. Much faster.
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Re: Can you heat treat small parts at home?

Post by RSG »

Thanks for the info guys.

Pete, I have watched the videos in the past of Clickspring heat treating but I didn't know it would apply to my application.

The parts are small, they are those disks I talked about in another thread made of SS (below) and I won't need to do many at a time. I figured 420 can be hardened so I might as well entertain the idea. I need these parts to last as I don't want to design a method to change them out. My preferred design is to press fit with locktite so as to void drilling and tapping.

Image

Interesting to learn about the MAPP gas.....I looked at the bottle I have and it reads "MAP/PRO" so I have no idea what that's about (See pic) so I'll have to google it. I do have access to acetylene if that's better.

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RSG
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Re: Can you heat treat small parts at home?

Post by RSG »

Just googled MAP/PRO, what a farce! 130 deg hotter then propane! Even Acetylene doesn't burn as hot as I thought.
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Re: Can you heat treat small parts at home?

Post by Bill Shields »

Ah yes...but mix it with oxygen and it gets hotter than most people need really fast.
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RSG
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Re: Can you heat treat small parts at home?

Post by RSG »

Bill Shields wrote: Sun Nov 21, 2021 2:09 pm Ah yes...but mix it with oxygen and it gets hotter than most people need really fast.
I assume you need a regulator or dual connector of some sort to blend them?
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Re: Can you heat treat small parts at home?

Post by Steggy »

Real MAPP Gas® is a mixture of methylacetylene, propadiene and propane. The only North American source of genuine MAPP gas shut down production in 2008. The products being sold today as MAPP gas are not MAPP gas at all and are inferior to the real McCoy. While MAPP gas substitutes do burn hotter than unadulterated propane, they do not burn nearly as hot as true MAPP gas.

The use of propane or MAPP gas to flame-harden parts may result in hydrogen embrittlement due to incomplete combustion. Oxy-acetylene is a better heat source since the fuel-air mixture may be adjusted to all-but-eliminate unburned hydrogen. That said, if I were regularly making parts that required heat treatment I'd construct a small natural gas-fired furnace with a blower so I can get better control.
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Re: Can you heat treat small parts at home?

Post by Harold_V »

Considering the size of the parts in question, a burnout oven commonly used by the dental industry (for investment casting) would be more than adequate. The chamber is exceedingly small, so the oven wouldn't take up much space and most likely would operate from the typical wall outlet.

Here's an example (although it's not specifically made for the dental industry):

https://www.etsy.com/listing/625067352/ ... ting_top-4

Note that I have no connection with the seller or maker of this product.

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