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To heat treat at home - or buy HT stock?

Just a Sparky

Just a Sparky

Hot Rolled
Joined
May 2, 2020
Location
Minnesota
Just started poking around on the local steel house's website as I'm taking down notes for my next material run and ran into a decision to make.

I'm looking at machining a new shaft for an old motor with bronze bearings and I now have to decide on an alloy and temper of steel to turn it from. The long and short of it is I've got so many other things floating around in my mind right now between this and other projects that I could really use a hand getting up to speed with heat treatment.

I need to make some bearing journals and I've got a lathe, sandpaper and an induction heater. Is heat treating 4140 something I should even waste time thinking about in a home shop environment? Should I just buy heat-treated stock and deal with any added difficulty which might be involved in machining it? Or would annealed 4140 be just fine for a V-belt drive bearing journal?

Thanks guys.
 
what kind of shaft? crankshaft? 4140 heat treated is an appropriate material for that. I've done lots heat treating at home for cutting tools over the years, but for a chrome moly part I don't think its worth it....buy the heat treated stuff. It machines fairly easily, i.e. its not anywhere near as hard as say hardened O1
 
Just a Sparky said:
Just started poking around on the local steel house's website as I'm taking down notes for my next material run and ran into a decision to make.

I'm looking at machining a new shaft for an old motor with bronze bearings and I now have to decide on an alloy and temper of steel to turn it from. The long and short of it is I've got so many other things floating around in my mind right now between this and other projects that I could really use a hand getting up to speed with heat treatment.

I need to make some bearing journals and I've got a lathe, sandpaper and an induction heater. Is heat treating 4140 something I should even waste time thinking about in a home shop environment? Should I just buy heat-treated stock and deal with any added difficulty which might be involved in machining it? Or would annealed 4140 be just fine for a V-belt drive bearing journal?

Thanks guys.
Click to expand...

I dont know what material you should use.....I can tell you that if you are talking about 4140PH ....It machines good. Nothing real special about machining it. The PH makes it sound tougher than it is.
 
Just a Sparky said:
Just started poking around on the local steel house's website as I'm taking down notes for my next material run and ran into a decision to make.

I'm looking at machining a new shaft for an old motor with bronze bearings and I now have to decide on an alloy and temper of steel to turn it from. The long and short of it is I've got so many other things floating around in my mind right now between this and other projects that I could really use a hand getting up to speed with heat treatment.

I need to make some bearing journals and I've got a lathe, sandpaper and an induction heater. Is heat treating 4140 something I should even waste time thinking about in a home shop environment? Should I just buy heat-treated stock and deal with any added difficulty which might be involved in machining it? Or would annealed 4140 be just fine for a V-belt drive bearing journal?

Thanks guys.
Click to expand...

If this is a running surface for a plain bearing, (so bronze on one side, this hardened shaft running in it), then the usual pre-hard 4140 will likely not be hard enough. If a ball bearing race will fit over the shaft, then sure, use commercial pre-hard.

In my understanding, you'll want a harder steel (mid 50's HRC and up) as a running surface. Which means not just HT 4140, but case/carburized to get the extra surface hardness needed. And then ground or polished to a fine surface.

Edit: I did find this, which indicates there are soft-enough bronzes out there to use with "regular" steel shafts:

"High strength is sacrificed for superior lubricity in the bronzes containing 15 and 25 percent lead, Alloys C93800 and C94300. These high-leaded tin bronzes embed dirt particles very well and conform easily to irregularities in shaft surfaces and permit use with unhardened shafts. As in all leaded bronzes the lead is present as discrete microscopic particles; in alloys C93800 and C94300 there is ample lead available to smear onto the journal to prevent welding and seizing, should the lubricant supply be interrupted. The lead also provides excellent machinability. "

Applications: Industrial - Selecting Bronze Bearing Materials

But if you don't know the alloy you're using I'd still err on the side of steel hardness.
 
I have heat treated on small job shops before only we did not call them that way back.

With the brass/bronze bushings there is a way to lubricate them well? Say with grease as is common. Usually these are designed such to do. If so this will extend the life where there is constant friction. As a rule where these were/are extensively used cutting oil grooves inside the bushings works well.

It is just something to look over and lubricate if at all useful.

The od grooves never go past the id to the other side of the bushing edges. The grooves on the id are designed to put grease in the bushing using the shaft - bushing fit to contain the grease in a running fit which keeps the softer bushing from wearing out too quickly by comparison with without grease lubrication.

It is not too messy really. This is how a lot of things were done short of having bearings. Still there is a great area of things which would be ok to do this kind of thing. In the field it might get something repaired and running until expensive items must be ordered and shipped in to do proper repairs - not band aid fixes per say.
 
They're circulating bearings with oil grooves fed by oil rings from a sump. Plenty of oil except in the first couple of seconds during startup.

Visual:
https://youtu.be/GjY6SGd7_lI?t=307

The 4140 I'm looking at is sold as either "4140 Annealed" or "4140 HTSR". The steel house also has 8620 but as I understand that's mostly a carburizing/case-hardening steel and is otherwise comparable to 4140.

My biggest concern is deflection of the steel during hardening and tempering. A couple of thou of deflection would be alright in this application but too much could cause the bearings to seize or the armature to impact the stator. Would induction heating be consistent enough to prevent/minimize this sort of warpage?
 
Induction heating the journals to an appropriate shade and dunking them in peanut oil. The rest of the shaft wouldn't really benefit from extra hardness. Just the journals.
 
You could probably "straighten" the parts between the journals to get it running in spec if it warped too much.

I don't expect a lot of warpage hardening a short length of a round shaft either.
 
I do not think you understand induction hardening journals or part of a shaft.
Where are your quench rings placed and timed how?
Heat all journals at once with multiple coils and drop it into the tank?
Bob
 
Not 'induction hardening'. Rather using an induction heater as my heat source for traditional oil hardening and tempering. Easier and more controllable with less risk of damage than an open flame.
 
OD of the journals are 0.810. The heater is untuned. Just a cheap little 750 watt circuit that runs at whatever frequency it feels like.

Not much power compared to a 10+kW industrial unit but it doesn't take a whole lot if a guy's not in a hurry. One horsepower concentrated into one or two cubic inches of steel will get red hot sooner or later.
 
you have to try it. no idea how you want to check temperature. i would want 850°c for 20 min., quench in 150°c oil vertically moving it, rinse in cold water for a while or even ice. then temper to 150°c for 20 min.

when machining leave generous radii and break the corners.

edit: oh, and start with pre-hard, it will machine better and should result in finer grain structure. you will have to protect the journals agains decarb somehow too.
 
Last edited:
I use a PID controlled kiln for heat treating special cutters, shafts, and tooling. The ramp, precise temperature control, and soak times are important for best results.
 
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