From where I might be able to source some 1300 micron (1.3mm) mild steel sheet?

[Michael GilliganParticipant @michaelgilligan61133]

Strangely enough, John … it didn’t seem particularly unreasonable to me:

I was simply observing that purchases would be more economical if ‘strategically planned’ rather than treating the Supplier as one’s Stores and calling-off ‘as required’.

They don’t owe the small consumer any favours.

MichaelG.

[duncan webster 1Participant @duncanwebster1]

Most thin sheet will be CR4, very low carbon, high ductility for pressing. As to why it has a large tolerance, well if you make things to a tight tolerance it costs more, so if it doesn't matter, you don't, and for most applications it doesn't. As others have said, design around what is available, or pay the cost of grinding it to size

[chris bale 1Participant @chrisbale1]

Best just find 1 10thou sheet and cut it 5 times! Or 2 .020s and a .010 if it really has to be 051 add a .001 too, by the time you have stacked them to .050 you will possible have too remove 1 of the 10s and swap for a 5-6thou.

Cromwell tools list .8 and .5mm at 30£ each for a roll or imperial mixed various from .001 to .015 6×12 sheets for 56£

[Pete.Participant @pete-2]

Posted by John Smith 47 on 19/10/2021 21:30:23:

Posted by Michael Gilligan on 19/10/2021 21:00:34:

Posted by peak4 on 19/10/2021 19:21:27:

If you're cutting it down and can get by with ½" wide, you could try HERE
https://www.repco-tech.co.uk/shims

Bill

.

That looks a useful Supplier, thanks Bill

[ noting that the minimum order value might encourage ‘strategic’ purchases ]

MichaelG.

.
[quote]

We have a £35 minimum order policy. Any orders under this value will incur an additional fee to adjust it to the minimum.

[/quote]

These sort of unfriendly barriers are actually pretty much out of date. I have talked to a few small-scale manufacturers and they seem to be quite irritated by this sort of thing.

It seems to me that to a quite a large extent the whole world is just thundering onto the likes of Amazon and the old tidy structures of wholesaler / distributor / retailer etc are just being crushed.

Edited By John Smith 47 on 19/10/2021 21:37:02

£35 isn't much, what would you expect their profit from a £35 sale is? it probably helps them avoid the time wasters.

[Dave SParticipant @daves59043]

[quote]

We have a £35 minimum order policy. Any orders under this value will incur an additional fee to adjust it to the minimum.

[/quote]

These sort of unfriendly barriers are actually pretty much out of date. I have talked to a few small-scale manufacturers and they seem to be quite irritated by this sort of thing.

It seems to me that to a quite a large extent the whole world is just thundering onto the likes of Amazon and the old tidy structures of wholesaler / distributor / retailer etc are just being crushed.

Edited By John Smith 47 on 19/10/2021 21:37:02

Seems reasonable to me.
It costs money to stock a thing, pick it, pack it, arrange postage and deal with any customer enquiries. I would be surprised if they actually make more than a couple of quid (end profit after all costs and taxes) on a minimum price order.

It also helps to keep time wasters away, the sort who as a load of questions and then buy a tiny amount never to be seen again.
Whilst it may seem an impediment to small businesses actually if a business can’t afford a £35 order it really isn’t much of a business.

Machining is a hobby for me, but I will buy from trade suppliers by making sure I order a good selection of both the things I need now and the stuff I’m likely to need before I can make another order upto the minimum amounts. That way I can access stuff the hobby supplier doesn’t stock, and often at a better price.

Dave

[Nigel Graham 2Participant @nigelgraham2]

If I recall correctly, the sheet material used in motor and transformer laminations is not steel.

It is pure iron, which allows the magnetism induced in it to rise and fall closely with the current cycles.

I do not know if or how this will affect your design but it may be a point to consider.

[noel shelleyParticipant @noelshelley55608]

Nigel is correct ! If magnetism is important to your design then you want lamination steel/ iron not mild steel. Noel.

[John HaineParticipant @johnhaine32865]

If you look at the earlier part of the thread the magnetic properties are pretty irrelevant as long as it is magnetic enough to work as some sort of latch.  And lamination iron even at 50 Hz is well under 1mm thick.

Edited By John Haine on 21/10/2021 09:49:25

[not done it yetParticipant @notdoneityet]

Posted by John Haine on 21/10/2021 09:48:17:

If you look at the earlier part of the thread the magnetic properties are pretty irrelevant as long as it is magnetic enough to work as some sort of latch. And lamination iron even at 50 Hz is well under 1mm thick.

Edited By John Haine on 21/10/2021 09:49:25

I would expect laminations to be thin to reduce eddy currents within the assembly?

[SillyOldDufferModerator @sillyoldduffer]

Posted by Nigel Graham 2 on 20/10/2021 22:38:52:

If I recall correctly, the sheet material used in motor and transformer laminations is not steel.

It is pure iron, which allows the magnetism induced in it to rise and fall closely with the current cycles.

Pedant alert. Though Iron was the original material you have to go back well over a century to find it in transformers. It was discovered early on that Silicon Steel is magnetically superior to Iron because it stores less residual magnetism when the AC field reverses.

Interestingly, Silicon Steel isn't much use for anything other than electromagnets because it's mechanical properties are poor.

Anyhow, the exact type of steel doesn't matter here because John is making a latch, where the exact magnetic performance of the steel won't make much difference.

In John's place, I'd try to avoid the problem of sourcing 1.3mm steel at the design stage by not depending on hard-to-get materials and odd sizes. Not easy – design is hard work, especially when you don't know what materials are available, how much they costs, or where to get them! John's difficulties are multiplied because he's short of space and money.

Faced with the problem of reducing a steel sheet to 1.3mm, I'd probably roll it – dead mild-steel is quite soft. Otherwise, glue the plate to a flat surface and sand it down with coarse Emery Paper. Takes time and effort but it will get the desired result at minimum cost.

John's goal being secret makes it difficult for the forum to suggest alternatives. This is unfortunate because there's more than one way of skinning a cat, especially in engineering! Rather than finding 1.3mm strip, how about padding out a thinner metal plate to fit with paper backing or epoxy?

Dave

[peak4Participant @peak4]

Posted by SillyOldDuffer on 21/10/2021 10:51:40:

…………………………..

John's goal being secret makes it difficult for the forum to suggest alternatives. This is unfortunate because there's more than one way of skinning a cat, especially in engineering! Rather than finding 1.3mm strip, how about padding out a thinner metal plate to fit with paper backing or epoxy?

Dave

My initial thoughts were to use 1.2mm steel and hold it in place with double sided tape before fixing with screws, but that wasn't what was required in the material spec.

Bill

[Tony Pratt 1Participant @tonypratt1]

You need to come up with a 'design' which uses obtainable materials.

Tony

[John HaineParticipant @johnhaine32865]

Posted by not done it yet on 21/10/2021 10:45:50:

Posted by John Haine on 21/10/2021 09:48:17:

If you look at the earlier part of the thread the magnetic properties are pretty irrelevant as long as it is magnetic enough to work as some sort of latch. And lamination iron even at 50 Hz is well under 1mm thick.

Edited By John Haine on 21/10/2021 09:49:25

I would expect laminations to be thin to reduce eddy currents within the assembly?

Again, if you look back, he's using a neodymium magnet so there are no eddy currents except transient when the latch closes or opens.

[speelwerkParticipant @speelwerk]

This one sells 1.30 mm C75 springsteel of 25 mm width **LINK** but no indication of minimum order quantity.

[Howard LewisParticipant @howardlewis46836]

If you want an easy release from the permanent magnet a shim of copper may do what you want. I believe that the pole, piece of a solenoid had a thin copper coating to prevent the armature sticking to the pole piece.after the current had been removed

Shim brass might do the same job..

Howard

[John Smith 47Participant @johnsmith47]

[I just lost a rather long reply]

In my experience everyone thinks that they understand magnetics but is an extremely hard subject.

It turns out that in practice (magnetic) "Permeability" is almost irrelevant and the only number that really matters for magnetic latches using permanent magnets is the (magnetic) "Saturation Flux Density".

Nobody will tell you this, but my understanding is that (roughly speaking) Permeability is how easily a material can start to be magnetised by a weak magnetic field, but Saturation Flux Density is how much you can magnetise a material… and it's the latter that matters most in practice!

Cheap mild steel (AKA Low Carbon Steel) seems to be be remarkably 'magnetic' in the sense of having a high Saturation Flux Density.

Despite being rather hard to machine, mild steel become incredibly easy to bend permanently when 1mm thick strips become long and narrow. For this reason I could always use spring steel and temper it, even though I am told that this would add "c. 20%" to manufacturing costs.

Of course the other problem with mild steel is that it does RUST very easily with fingerprints and would presumably need to be electroplated. I might consider some kind of 'magnetic' (i.e. Ferritic or Martensitic) surgical steel but from what I can see they will create about half the magnetic pull of mild steel. Also one would need to be careful as most grades seem to be about as soft as mild steel.

Tricky stuff, eh?

[Michael GilliganParticipant @michaelgilligan61133]

If we knew what you were trying to make, John … People might be able to offer useful comment, based on their experience.

But as it’s all confidential : “Tricky stuff, eh?” is probably a good summary.

MichaelG.

[Dave SParticipant @daves59043]

I’m not sure I agree with “Tricky Stuff”.

Possibly “narrow specialism, niche application stuff”

Magnetic properties of materials is a specific area of materials science, and a well studied one at that.

The information is available, it’s just not actually that critical to most applications.

Dave

[John Smith 47Participant @johnsmith47]

Posted by Dave S on 26/10/2021 19:51:09:

I’m not sure I agree with “Tricky Stuff”.

Possibly “narrow specialism, niche application stuff”

Magnetic properties of materials is a specific area of materials science, and a well studied one at that.

The information is available, it’s just not actually that critical to most applications.

Dave

You could probably say the exact same thing about doing surgery on the human brain or about sending a rocket to the moon. In fact.. just a wild guess, Dave, but… maybe you do! ;^P

J

[John HaineParticipant @johnhaine32865]

Posted by John Smith 47 on 26/10/2021 18:40:31:

…..

In my experience everyone thinks that they understand magnetics but is an extremely hard subject.

It turns out that in practice (magnetic) "Permeability" is almost irrelevant and the only number that really matters for magnetic latches using permanent magnets is the (magnetic) "Saturation Flux Density".

Nobody will tell you this, but my understanding is that (roughly speaking) Permeability is how easily a material can start to be magnetised by a weak magnetic field, but Saturation Flux Density is how much you can magnetise a material… and it's the latter that matters most in practice!

….

Hmmm. How close you can get to saturation depends on the flux density produced by a given magnetic field, and so on the permeability. So for the unmagnetized polepiece of a latch you want a material that has high permeability but also a reasonable saturation flux density, but low remanence so it doesn't itself get magnetised. There's a distinction between field and flux, which roughly speaking correspond to voltage and current. But in the end mild steel is probably a reasonable compromise and for most simple magnetic devices is as good as you need.

**LINK**

[John Smith 47Participant @johnsmith47]

Posted by John Haine on 28/10/2021 10:14:36:

Posted by John Smith 47 on 26/10/2021 18:40:31:

…..

In my experience everyone thinks that they understand magnetics but is an extremely hard subject.

It turns out that in practice (magnetic) "Permeability" is almost irrelevant and the only number that really matters for magnetic latches using permanent magnets is the (magnetic) "Saturation Flux Density".

Nobody will tell you this, but my understanding is that (roughly speaking) Permeability is how easily a material can start to be magnetised by a weak magnetic field, but Saturation Flux Density is how much you can magnetise a material… and it's the latter that matters most in practice!

….

Hmmm. How close you can get to saturation depends on the flux density produced by a given magnetic field, and so on the permeability. So for the unmagnetized polepiece of a latch you want a material that has high permeability but also a reasonable saturation flux density, but low remanence so it doesn't itself get magnetised. There's a distinction between field and flux, which roughly speaking correspond to voltage and current. But in the end mild steel is probably a reasonable compromise and for most simple magnetic devices is as good as you need.

**LINK**

Permeability vs Flux Saturation Density

I notice your link fails to even mention Mild Steel.

Well, when I first researched this topic, I thought sounded like it would be all about (magnetic) Permeability. And the Permeability numbers certainly vary dramatically, as your link demonstrates.

If you also think Carbon Steel is close enough to Mild Steel, think again because Ferritic Stainless Steel has a much higher Relative Permeability. "100" plays "1000 – 1800"…

i.e. If it was all about permeability Ferritic Stainless Still would have at least x10 the magnetic pull compared to Carbon Steel (and you might thought Mild Steel). But we know that if anything it's the other way around!

[See how "tricky" this topic is!]

The fact is that in practice, when using standard modern high-strength neodymium magnets, it turns out that the saturation flux density is vastly more important than Permeability. For example in my experiments both in FEMM and in the real world, a Ferritic Stainless Steel will have c. 30% to 40% LESS magnetic pull than Mild Steel has.

And in this regard the best ferromagnetic steels available don't perform all that much better than mild steel. From memory the uplift in magnetic pull was only something like +30% or +40% (??) and meanwhile the costs started to escalate.

"magnetic field" and "magnetic flux"
TBH, I never did feel that I 100% understood the difference between "magnetic field" and "magnetic flux". I think magnetic field can be thought of as the strength (i.e. total energy) of a magnet, whereas the flux is how concentrated those lines of force are within a specific area.

Remanence
My thinking is that I don't care about remanence AT ALL. The latches are not being turned on/off electrically. In fact they are using permanent magnets and simply use physical separation. i.e. The are very similar to how a magnetic kitchen/wardrobe door closure 'sandwich' works.

i.e. When the door is open the magnetic sandwich is far enough from the steel that they close on to as to not have any tendency to close the door. i.e. If the steels within the 'sandwich' stay magnetised that isn't a problem. Likewise if the steel that meets them stays magnetised (by them) that sounds fine to me too. So unless any remanence is fighting the magnet, I think I can forget about it.

One thing I have noticed is that even though when you separate the steel from the magnets, the steel do not stay significantly magnetised, if you leave the magnets in place for a few seconds the magnetic pull SEEMS to gradually get quite a lot stronger in a matter of say a few seconds. This may be some kind off illusion I'm not sure, but I as far as I can tell it doesn't appear to be caused by the magnets slowly moving closer to each other. Either way if the magnetic pull is good enough immediately and if it gets say twice as strong in a few seconds that's fine by me.

But the main point is that my magnetic assemblies work really well which is all I really need to know!

[John Sykes 1Participant @johnsykes1]

The "pull" of the magnet is actually calculated from the incremental change in stored energy in the air gap as the pole piece (or whatever) is moved towards or away from the magnet. Many non-linearities will render precise calculations of absolute magnetic flux somewhat futile, but the general principle is there, and tells is that the pole piece should have a high saturation figure and should be adequately thick to handle the total flux generated by the magnet (if the objective is to obtain the maximum force). You can observe this phenomena using a magnetic dial-guage holder, first on thick cast iron, and then on a thin plate, where the force is much reduced. The surface roughness / flatness also comes into play when considering the maximum "pul-off" force, as any residual air gap when the parts are touching will impact on the "closed loop" flux density.

BTW, 1.3mm is very close to 16 AWG !

[Author]

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