Accurate sheet metal cutting

[R Smith 1Participant @rsmith1]

Hello All.

I would be grateful for some advice on the best tools & equipment for making fine cuts in sheet metal. I am a long time woodworker, but when it comes to any metals, I'm pretty hopeless and clueless, so apologies for daft questions.

I am looking to experiment with making some accordion reeds, which involves cutting reed tongue blanks out of ~0.6 sheet spring steel. Ideally, the cuts shall be reasonably accurate (say, within 0.5-1.0 mm) and they shall not bend & deform the sheet steel.

A simple example would be to start with a strip of 8mm-wide spring steel, and then, along the first 40mm of the strip, cut a 1-2mm off from both edges, without making a pig's ear of the remaining ~4-mm wide strip in the middle. It seems that bog standard tin snips are unable to make such cuts without severely bending & deforming the blank.

Would something like a manual sheet nibbler work well? Some special shears perhaps?

Thank you.

[R Smith 1Participant @rsmith1]

[DC31kParticipant @dc31k]

If the maximum you want to remove from each side is 2mm, use a file.

Specifically, use a coarse file for the first 1.5mm and a fine file for the remainder.

Clamp the spring steel between two larger, stiffer pieces of metal with the line to which you will file a tiny bit (the thickness of a sheet of paper) above the clamping metal.

If you are confident, use a disk or belt sander. Glue the steel to a block of wood to make it easier to hold. Be careful not to overheat it.

[An OtherParticipant @another21905]

I wouldn't claim to be an expert, but I have made some very thin spring plate valves for a ramjet – round about 0.5mm thickness. I found the best way to cut them was to use a thin cutting wheel in a Dremel-type tool – when I bought the tool, it came with thin brown cutting wheels about 1" diameter.

It was a little difficult, since I was cutting free-hand to a stencilled pattern shaped like a daisy, but I am assuming your accordion reeds are straight, so it may be a little easier. I would suggest that perhaps you could make a small jig to clamp the steel and hold it, then cut up to the jig to get the size correct and constant ?

I found almost any type of blade cutter (snips, etc), tended to leave a very slight 'tipped-up' edge on my valve springs – my problem was that the heat of the ramjet motor heated these edges very quickly, and then they burnt away – shouldn't be a problem in an accordion, I guess, unless you are a demon player

[Dave HalfordParticipant @davehalford22513]

If you know someone with a Plasma cutter he can help.

[Clive SteerParticipant @clivesteer55943]

One way to make small thin parts is to coat the thin material with beeswax , scribe the outline of the reed and then acid etch. Laser or plasma cutting may produce hardened edges if the reeds are steel. Water jet cutting works on most materials but cannot be done at home.

I believe the rate of etching can be increased electrically.

CS

[martin haysomParticipant @martinhaysom48469]

Posted by R Smith 1 on 21/06/2023 07:44:39:

Hello All.

. It seems that bog standard tin snips are unable to make such cuts without severely bending & deforming the blank.

Thank you.

if used correctly all the distortion will be on the off cut and the job remains flat

[Ady1Participant @ady1]

Plasma and laser messes up the edges and you need good edges

A decent guillotine would do it

for really good cuts you probably need to make a special jig that holds the reed part between vice type jaws, wood or metal, and the protuding part is cut off with a guillotine or dremel or a decent small grinder with a 1mm disc

So a bench vice and a dremel/grinder and some practice would get you a few one offs

If you want no bends and very close cuts then sandwich the sheet between two pieces of sacrificial wood in the bench vice and use a good hacksaw blade. Move the arrangement as you cut each slot for maximum support for each cut.

Edited By Ady1 on 21/06/2023 18:24:17

[R Smith 1Participant @rsmith1]

Thank you very much.

Must have mentioned – I just want to hog off the material before I start fine-fitting with a file.

Filing has so far been the option that I tried, and it seems to take a lot of time, hence me looking for some way to cut.

Sanding, dremel, etc – I will probably overheat the metal and harden it.

Don't have a CNC laser or plasma cutter.

I'm using CS95 steel for the prototype, because that's what I had kicking about the workshop.

[DC31kParticipant @dc31k]

Posted by R Smith 1 on 21/06/2023 18:22:19:

Sanding, dremel, etc – I will probably overheat the metal and harden it.

Do you have a Tormek in your woodworking kit? That would do the trick.

Sanding would work with care. Apply to the disk for maybe one second and then dip in some water.

[Speedy Builder5Participant @speedybuilder5]

Easy peasy – follow this link. There may be a couple of advert videos before you get to "How to do it" bit.

Etching thin valve discs

[R Smith 1Participant @rsmith1]

No tormek – I'm an old school bugger. A piece of glass & abrasive paper to keep the edges razor sharp.

Thank you Speedy – I guess that can be the solution to mass-etch them once I've prototyped the sizes.

[Ady1Participant @ady1]

Awesome link

I wonder if he's the same pulse jet guy who was asked by the NZ government to stop giving info out on how to make your own V1 type unit

[An OtherParticipant @another21905]

Link Some more data – lots more available online. Love to have watched them plasma-cutting a hundred years ago

[R Smith 1Participant @rsmith1]

Ironically, a plasma cutter will set you back less than a clicker press with a set of custom dies…

[Kiwi BlokeParticipant @kiwibloke62605]

Ady1 – yes he is (and I don't know him, officer). A national treasure!

[Kiwi BlokeParticipant @kiwibloke62605]

R Smith 1 – There are, or used to be, people in Italy who spent their working lives making reeds. It's a specialised craft, and no doubt some of the techniques were kept pretty secret. However, videos are around that show a little of the process. You've probably already discovered that, apart from the profile of the reed having to be accurate enough to fit the aperture in the reed plate with minimal clearance, the reeds can vary in thickness along their length. And then, for bass reeds, have lumps of brass soldered to their tips. Complicated things!

I'd imagine that the blanks were guillotined and then fettled by belt sander and file – a finniky and slow job…

Good luck. I also have an accordion I'm (occasionally and very slowly) rebuilding.

[Kiwi BlokeParticipant @kiwibloke62605]

Another thought. Beware, abrasive cutting may heat the reed enough to change its temper.

[bernard towersParticipant @bernardtowers37738]

can you not sandwich the spring steel between two 4mm strips of steel and mill with carbide cutter. if stacked they will come out very clean

[R Smith 1Participant @rsmith1]

Thanks.

I should have mentioned that I've been building guitars and mandolins for a decade, so not new to creating things that make noise .

The secret knowledge bit is overrated – most things are straightforward, but one needs to be able to separate disinformation from various forum "gurus", out-of-date books and traditions from things that actually matter to making a good instrument. A lot of the time, things are done in a traditional way without anyone ever questioning why everyone's doing it that way…

Complex – yes. But it doesn't need to be more complex that it is. I'm a lot more concerned about my ability to cut accurate slots in alloy and then fine-fitting the reeds. So this will probably be a fail, but hey, it's better than wasting your time watching tv, right?

In most cases you can find all the solutions yourself by experimenting.

[R Smith 1Participant @rsmith1]

bernard – thank you for the suggestion. I've been looking for an excuse to buy a milling machine for a few years now, and that's an option. I haven't thought about the sandwich thing though.

[R Smith 1Participant @rsmith1]

Apologies for an even dafter question: I see that Axminster has the SX1 mini mill on discount.

Is there much that I need for milling aluminium (3-7mm) and thin brass(3-4mm)? Afaik I don't even need to lubricate – just stick a cutter in and go?

[Kiwi BlokeParticipant @kiwibloke62605]

Do you really need to go down what can turn out to be a very deep and expensive rabbit hole? A milling machine needs to be equipped, even for simple jobs. You'll need work-holding equipment (vice, clamps, etc.), work setting equipment (parallels, V-blocks, edge finder, etc.), drill bits and milling cutters (so many choices…), chucks, metrology equipment, and so on and so on. And then you'll need the background information about cutting speeds and feeds, and so on. You'll also need to accept the limitations – or take steps to overcome them – of a little machine that may not be the best engineered…

Thin sections of soft metals can be easily worked by hand, and accuracy can be aided by the use of improvised jigs and fixtures. Files are wonderful things, but you've got to be prepared to buy the correct ones for your application(s) and preferred way of working. Buy good makes (eg Grobet, Vallorbe), and you'll wince at the price, but they're well worth it.

I would think that most accordion reeds start as blanks, punched from spring steel sheet or strip. This would allow the wider part around the rivet hole to be formed at the same time as the thinner vibrating part., and all pretty much free from distortion. The desirable 'hand-made' reeds start as a strip, the same width as the part around the rivet hole. Their characteristic blue edge beside the rivet hole is the blue edge of the parent strip stock. In these reeds, I don't think the tongues could be punched to width, so perhaps the tongues are, in all cases, formed entirely by machining. The apertures in the reed plates are, I believe, broached. And then an old gaffer in a ramshackle Italian cottage-factory got to work with files (or a filing machine if they were flush) and abrasive belt sanders. Or you could buy them… Stick 'Carini de.na.' into your search engine: I can't remember whether bare tongues are available from there, but everything else is.

[KenLParticipant @kenl]

Am I being naive or is there really any need for complex solutions for cutting thin sheet without distorsion?

I can't believe that no-one has suggested a Monodex cutter (search on Ebay).

I haven't used one for years but ISTR that they did not distort the metal at all.

The drawback side is that you need some stamina to use them for all but the thinnest sheet.

[Kiwi BlokeParticipant @kiwibloke62605]

The OP's application is for work finer than a Monodex (or similar) can produce. Actually, quite a challenging task.

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