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Cutting Stainless Steel
Posted by
bostonman
on 10 Jan, 2024 16:49
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I have 3/8" x 24 SS threaded rod and need to cut it to size.
From reading, ignoring cutting methods, stainless steel will not rust when cut. The stuff that will be cut is: 3/8" x 24 SS, 8-8 Rockwell B70 (McMaster-Carr part number: 98920A307)
My general question is whether the size matters. As an example, if I had a 12" x 12" block of stainless steel, and I cut it in half (ignoring the difficulty of cutting it), would that rust since it's such a large surface area was cut, or would it still be equally resistant to rust?
Also, does the SS need time to develop a "coating" once cut to prevent rust or can it be (hypothetically) cut under water and remain under water without rusting?
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stainless steel will not rust when cut.
But may form corrosion.Soak the cut end in some lemon juice for a few hours to repassify the surface
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#2 Reply
Posted by
bostonman
on 10 Jan, 2024 17:47
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Corrosion in the sense it will spread over time and rot the rod or just be an eye sore?
Interesting about the lemon juice... I'll keep this in mind when I cut it.
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#3 Reply
Posted by
jpanhalt
on 10 Jan, 2024 18:00
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I could not find 8-8. Perhaps you mean 18-8, which is also called 304. It is quite common, and I have had no problem with corrosion after cutting it even without further treatment. The key is heat. For a rod like that, you can probably cut it with a hacksaw. If you use abrasive cutting, be careful of the heat. It also work hardens, so be sure to apply enough pressure to keep cutting and avoid surface hardening.
Lemon juice has both ascorbic acid and citric acid. The majority is citric acid. Ascorbic acid is a reducing agent. Citric acid alone is cheaply available and is used for passificttion.
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#4 Reply
Posted by
bostonman
on 10 Jan, 2024 18:07
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Sorry, yes, 18-8 (I had included the McMaster-Carr part number for reference too).
If I understand the visual correctly, as the SS heats while cutting, it becomes harder making cutting more difficult?
Again, hypothetically, if I were to cut 12" x 12" block and I did it really fast with say a high speed band saw, what would technically happen? The SS would become harder and harder until it did what?
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#5 Reply
Posted by
Benta
on 10 Jan, 2024 21:28
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Some SS types are inded prone to work hardening, and will turn almost as hard as glass on the surface. Once that happens, your workpiece is dead. All that's left for saving it is grinding.
The secret is low surface speed, heavy feed and medium DOC (you need a sturdy machine) and lots of cutting fluid. Never let off on the feed, but keep going.
Not all SS steels are like that, machine-friendly alloys exist. It's a science.
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I wonder if the milwakee threaded rod cutter could handle it.
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#7 Reply
Posted by
SeanB
on 10 Jan, 2024 21:55
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Yes cutting stainless steels you keep them cool, using either cutting paste, or coolant flow. With a hacksaw cutting paste works well, as it provides lubrication to the sides of the blade, and removes the chips, but with a power saw you want coolant flow.
As to passivating again simply leaving in open air for a few hours will passivate it again, though it can be assisted by cleaning with neutral detergent, and rinsing off, to allow air to reach the surface and oxidise the chromium. You can hasten it with acid, normally a mild organic acid, typically oxalic acid, which is toxic, so often substituted with acetic acid instead. I have used ascorbic acid before, and asprin also works in a pinch, and also is a good flux to use to clean off oxide when brazing.
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#8 Reply
Posted by
pickle9000
on 10 Jan, 2024 22:01
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Per the original question, stainless steel is an alloy.
Heat and may change its colour hardness, but assuming it was perfectly cut it's the same all the way through.
Changing the mix like changing the recipe for a cake makes stainless more or less prone to oxidation.
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#9 Reply
Posted by
T3sl4co1l
on 11 Jan, 2024 15:23
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As I'm fond of saying... it's stainless, not stainproof!
Typically an un-passivated surface only incurs cosmetic corrosion -- staining, and does not accumulate rust as such. Or if it does, the rate is extremely low.
Rust staining is still a rough and porous deposit, so it can trap bacteria and hence passivation is obligatory for food handling equipment, for example.
There are stainlessless alloys out there, with less chromium and nickel, still enough to slow corrosion, but not to stop it outright -- COR-TEN brand for example. They might be rated in terms of specified material loss rate under given weathering conditions, and take on a notably brown patina, but survive well for infrastructure (when you don't mind the staining). Hence many bridges, towers, sculptures, etc. made from the stuff.
Basically, you can imagine passivation, or the lack thereof, being a step on the continuum of such a process. 304, 316, 18-8, etc. are on the "negligible" end of the material loss rate spectrum.
Considered in this framing, even mild steel might be acceptable for certain applications, certainly so when the environmental conditions are more mild, or protection is available (oil, paint, etc.), but also where shortdefined lifetime is acceptable given the cost -- automobiles for example.
Regardless of alloy, you need the usual trifecta for corrosion: water, oxygen, and electrolyte. If this is an indoor application in most regions, I wouldn't worry about it, and something like galvanized rod with paint dabbed on the cut end will last ~forever. If condensing humidity is a common occurrence (as can be in some particularly rainy corners of the world, PNW for example), even the salt from ambient dust can suffice to catalyze corrosion, and galvanizing paint or dip might be desirable, or indeed using stainless.
I forget if you mentioned you're in coastal Boston or what. Sea spray, and, say if it's mostly indoors but like a garage regularly open to outside air, that would be marginal enough I'd probably want stainless, and passivation if it should look good or remain hygienic.
Tim
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#10 Reply
Posted by
langwadt
on 11 Jan, 2024 15:39
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it not hardenend by heat, it work hardens so you must make sure to have enough feed to alway keep the cutting under the hard surface, as soon as things start rubbing instead of cutting you are screwed
and don't use grinders etc. that have been used for regular steel, it'll contaminate the stainless and make it rust
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#11 Reply
Posted by
jpanhalt
on 11 Jan, 2024 15:56
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it not hardenend by heat, it work hardens so you must make sure to have enough feed to alway keep the cutting under the hard surface, as soon as things start rubbing instead of cutting you are screwed
and don't use grinders etc. that have been used for regular steel, it'll contaminate the stainless and make it rust
I agree on the work hardening. If I gave the impression that heat was the cause, I didn't mean to. The problem with heat is decreased corrosion resistance due to changes in the alloy and color change.
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#12 Reply
Posted by
IanB
on 11 Jan, 2024 16:03
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I have 3/8" x 24 SS threaded rod and need to cut it to size.
Then cut it, like anyone else would do, with a hacksaw.
Again, hypothetically, if I were to cut 12" x 12" block and I did it really fast with say a high speed band saw, what would technically happen? The SS would become harder and harder until it did what?
Why would you be getting distracted with hypotheticals? It's a waste of brain cells, when the answer is going to be "it's complicated, and it depends on many factors". Are you planning to spend years learning about material science and machining?
Leave the hypotheticals on one side just get on with the job. Learn from experience. Cut your rod with a hacksaw and watch what happens. Make a test cut before you make the final cut so you can see if anything needs adjusting.
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#13 Reply
Posted by
bostonman
on 11 Jan, 2024 16:36
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Why would you be getting distracted with hypotheticals?
Great point. Often times I use hypotheticals as a way of learning how far I can push something before it breaks, corrodes, warps, etc... If the answer was cutting a 12" x 12" block of SS down the middle and it wouldn't rust/corrode, then I'd be confident 3/8" rod is a walk in the park.
Doesn't mean using hypotheticals is correct, but just pointing out my way of thinking and why my questions/replies may deviate towards them.
This thread has been very useful. Prior I never heard the term 'work hardening'. I'll but sure to take the advice when cutting this rod. I don't have 'cutting paste', but will either get some or use plenty of oil (the cutting tool will be a hacksaw). After I'll wipe the shavings off, and, since this will be already mounted vertically, maybe just put a cut lemon on top.
As asked, I'm not on the coast. The cut end will be in an attic where it can go from freezing to 120 degrees F in the summer. I could have went zinc plated (assuming they come in the size/length I needed), but feared cutting the end, scratching, etc... would cause the plating to come off and thought the SS was worth the extra few dollars.
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#14 Reply
Posted by
IanB
on 11 Jan, 2024 16:48
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My advice: do some experiments.
Take a scrap end of the rod and just try cutting it dry with a hacksaw (use a fresh blade). Use a fine tooth blade suitable for hard metals. See how it goes and observe any problems.
If something doesn't go well, make a change and try again, for example use a drop or two of oil when cutting. Or try a different hacksaw blade with a different tooth size. Or try using a cut-off wheel on a rotary tool.
Build up your experience from such tests, and then when ready, make the actual cut to the desired length.
I don't see the need to mess around with lemon juice. Stainless steel will passivate itself given time. Even if a few bits of corrosion appear on the cut end, it doesn't matter. It won't affect anything mechanically.
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#15 Reply
Posted by
bostonman
on 11 Jan, 2024 18:36
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Good idea. Maybe I'll try a SS screw instead rather than sitting in a cold attic cutting sideways to experiment.
Now I also understand why drill speeds for SS are low.
What happens with a larger diameter bolt if someone were to grind it with a grinder with a cutting wheel? I assume 3/8" would cause less "work hardening", but would the larger diameter bolt eventually prevent the grinder from cutting and the person would just grind away the wheel?
I don't have an angle grinder or a very large SS bolt to experiment, so I'm curious whether the bolt actually gets strong enough so it can't be cut.
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#16 Reply
Posted by
IanB
on 11 Jan, 2024 18:48
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Good idea. Maybe I'll try a SS screw instead rather than sitting in a cold attic cutting sideways to experiment.
It's unfortunate that the rod is already installed. The ideal would have been to cut it to length before installing it.
I don't have an angle grinder or a very large SS bolt to experiment, so I'm curious whether the bolt actually gets strong enough so it can't be cut.
I was thinking something more like a Dremel than an angle grinder. If you used a diamond cutoff wheel it will always cut.
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#17 Reply
Posted by
jpanhalt
on 11 Jan, 2024 18:52
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If it's in the attic, why bother cutting the end off? You might want to lower the bookcase some day.
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#18 Reply
Posted by
T3sl4co1l
on 11 Jan, 2024 18:58
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Note, you want a high-pressure lubricant; if you don't have cutting oil specifically, just something like bacon grease will do alright. The old fashioned way, pre-synthetics...
Tim
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#19 Reply
Posted by
bostonman
on 11 Jan, 2024 19:18
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It's unfortunate that the rod is already installed. The ideal would have been to cut it to length before installing it
It's not already installed, but I'm uncertain of the exact supporting method I'll use, therefore, I don't know how much length I'll need.
You might want to lower the bookcase some day.
You have me thinking now. I'll consider it, but I've given this extensive thought and most likely I'll never lower it; plus the rod sticking up is a possible hazard (not that it's livable space).
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#20 Reply
Posted by
langwadt
on 11 Jan, 2024 20:47
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Good idea. Maybe I'll try a SS screw instead rather than sitting in a cold attic cutting sideways to experiment.
Now I also understand why drill speeds for SS are low.
What happens with a larger diameter bolt if someone were to grind it with a grinder with a cutting wheel? I assume 3/8" would cause less "work hardening", but would the larger diameter bolt eventually prevent the grinder from cutting and the person would just grind away the wheel?
I don't have an angle grinder or a very large SS bolt to experiment, so I'm curious whether the bolt actually gets strong enough so it can't be cut.
a cutting disc on an angle grinder doesn't care if the stainless is hardened
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#21 Reply
Posted by
jpanhalt
on 11 Jan, 2024 21:33
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a cutting disc on an angle grinder doesn't care if the stainless is hardened
He seems to be preoccupied with the possibility of rust on the top mm of a bolt in the attic. Frankly, if the "danger" of a bolt sticking up is his other concern, a long extension is more likely to be seen and avoided than a much shorter one. Think of stepping on a Lego. Moreover, it could be painted with fluorescent orange. Is his attic open to the public?
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#22 Reply
Posted by
langwadt
on 11 Jan, 2024 21:59
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a cutting disc on an angle grinder doesn't care if the stainless is hardened
He seems to be preoccupied with the possibility of rust on the top mm of a bolt in the attic. Frankly, if the "danger" of a bolt sticking up is his other concern, a long extension is more likely to be seen and avoided than a much shorter one. Think of stepping on a Lego. Moreover, it could be painted with fluorescent orange. Is his attic open to the public?
yeh it is all rather silly. don't cut it, cut it, use a hacksaw, angle grinder or an angry beaver, it doesn't make a hoot of difference
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#23 Reply
Posted by
bostonman
on 12 Jan, 2024 03:20
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a cutting disc on an angle grinder doesn't care if the stainless is hardened
From the explanations, the visual I had was the SS gets harder and harder and would eat up the cutting disc before being cut.
He seems to be preoccupied with the possibility of rust on the top mm of a bolt in the attic. Frankly, if the "danger" of a bolt sticking up is his other concern, a long extension is more likely to be seen and avoided than a much shorter one. Think of stepping on a Lego. Moreover, it could be painted with fluorescent orange. Is his attic open to the public?
Okay..... that was hilarious.
Remember, at least a 4x4 will be laid across, so most likely nobody is stepping on it without seeing the wood first. In any case, that comment was hilarious.
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Thinking of extreme cases is sort of OK if you think broadly enough.
For example. Your 12 by 12 SS block. You envisioned that it would get harder and harder until the grinding wheel became the softer item and went away.
Now think broadly about it. If it got that hard you would live in a world that was flooded with work hardened stainless steel tools. No one would bother with HSS steel or carbide inserts. That thought would lead you to the correct result that the SS hardens but not indefinitely. Just enough that it is hard to impossible to cut with common tooling.
This is an example of getting a bit of data in a case where you are extrapolating beyond the known data. Extrapolation is always dangerous, so should be used with great caution, and tests performed to find if there is any reason to believe that the extrapolation will hold up.
I have personally followed the back yard mechanic's path, similar to the bumblebees path. No one has told them they can't do what they do, so they don't worry and it works. I have cut stainless rod with a hacksaw and other tools without major difficulty. I have only occasionally encountered the hardening issue, and when it occurs rotating the rod and cutting from a different direction avoids the hardened region until the rod can be snapped off (remember hardness and ductility are inversely related). The end can be ground smooth if desired.