advice sought - what cutting bit material for cutting thin stainless steel sheet?

Hello
"tungsten carbide or diamond grit coated or carborundum?"
I need to cut a couple of circular holes (150mm dia) in some 0.5mm thick "304" grade stainless steel sheet which has been formed into a curved shape and polished (which I think means it has likely been work hardened).
I have decided upon a Dremel type of tool, perhaps with some lubricant on the work piece, and adjustable speed. I think a grinding type of bit, e.g. a 3mm cylindrical "burr", will suit. This is the sort of bit shape I hope to try:
http://i.ebayimg.com/images/g/7xsAAOSwBahVOawQ/s-l1600.jpg
or
https://cdn.ecommercedns.uk/files/2/203492/3/955073/3mm-carbide-cutting-burr-round-cylinder.jpg
I can buy them made from tungsten carbide, or diamond grit coated, or the "carborundum" type of grinding stone.
Which is likely to be best? I can see that the cost of any of the types if affordable for me and I don't need to make hundreds of cuts - I want to use which is going to give me the least heating distortion and is likely to be the fastest to cut.
Thanks for any advice on which type to choose!
DDS
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On 2/3/2017 12:24 PM, Duncan DiSaudelli wrote:

The problem I always have with burrs and grindstones is keeping them on track.
All 18-8 stainless steels are buggers for finishing with hand-held tools. The curved shape implies some work hardening, but the original sheet will have already been work hardened by rolling. The benefit from the shaping means that it will be much stiffer than a flat sheet, hence on balance easier to work.
If it was thicker, I think I might rough them out with a slitting disk in a 125 mm angle grinder. At 0.5 mm, I'd be inclined to start by using a Dremel with the fibre-reinforced slitting disk, without lubricant. The disks won't last all that long. I say no lubricant because of the difficulty of maintaining supply. You will get the fastest cut using the thin, brittle, non-reinforced disks but they will break if you apply any out-of-plane load.
One you have roughed out the cut, I would use a cylindrical abrasive bit. The ones which fit a dremel will be rather small for cleaning up a peripheral length of half a metre. You would be better off with a die grinder, and abrasive bits perhaps 25 mm diameter.
You might be able to do the stage between Dremel "rough cut" and Dremel "final finish" using a standard grinding disk on a 125 mm angle grinder. Much faster metal removal. Some care needed!
0.5 mm is *probably* just too thick to use a shears. You can get "Gilbow" type shears with curved blades to help making curved rather than straight cuts.
IIRC this "universal" type will also cut curves, at a price!
(Amazon.com product link shortened)86142651&sr=8-8&keywords=gilbow+shears
Might be worth checking if you happen to have a normal (straight) shears.
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Hello newshound

You've made some good points and your mentioning of "die grinder" has shown me that this might be a better purchase than a dremel. I can see some very affordable ones, and the bits for them are likely to be heavier duty. I remember coming across the term before but I didn't know what it meant. Now I can see it might suit me very nicely.
My plan is to fix the rotary tool (of whichever type I buy) to a bench and then, by hand, introduce to the bit and then rotate the work piece about its axis, in order to be able to control the feed rate. The axle can be bolted to the same bench and I am confident that I will be able to form a nice circle.
I think a die grinder with suitable clamping should work very well, and thanks for the advice. I shall look into the cutting disks you mentioned & I'll see what types of other cutting bits are available (I still think a burr approach might well suit this particular task).
Thanks
DDS
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On 03/02/2017 19:35, Duncan DiSaudelli wrote:

Maybe something like this?
(Amazon.com product link shortened)
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dennis@home wrote:

This is the best solution by far.
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dennis, F Murtz - I didn't realise that that sort of "nibbler" would be as affordable. I will see if it would work for my particular set of circumstances. Thanks for the suggestion and recommendation.
DDS
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Had a go using some air power tools in a garage a while ago, that above seems like a very good investment:)
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Tony Sayer




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You'll end up with a shed floor covered in tiny 1/8th. Moon chips:-)
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Big magnet;)
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wrote:

If it is a magnetic stainless steel.
G.Harman
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On 2/6/2017 12:40 PM, snipped-for-privacy@yahoo.co.uk wrote:

But 304 isn't.
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Yup. One of the speakers on my old Rover as I discovered after having a new rear wing fitted. The type of car speaker with a concentric tweeter - so no grill over the pole pieces. Which filled up nicely. ;-)
--
*I couldn't repair your brakes, so I made your horn louder *

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A discovery from 55 years ago (apprentice tour of duty in the instrument dept.) a sharp steel pointed tool (broken dart ideal) is that you can pick out bits of steel from a circular magnet.
Presumably the magnetic field is stronger at the point.

--
Tim Lamb

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On 2/3/2017 8:20 PM, dennis@home wrote:

I had one of them (from Machine Mart). The "bit" broke after rather limited use and I couldn't get a replacement. They are certainly good on steel or aluminium and should work on 0.5 stainless, but as I said before it is a really difficult material to work with in this way.
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dennis@home.?.invalid writes

I have one of those. Pretty aggressive for precision work and you obviously need a supply of compressed air.
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Tim Lamb

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On 04/02/2017 10:35, Tim Lamb wrote:

I have some air shears, they are aggressive. I had a hand operated punch that worked well, its has gone somewhere but I don't know where.
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You can get hand operated nibblers too. Preferably one where you can buy new jaws easily if cutting SS.
I've got a rather rare electric version - made by Hitachi. Does tend to run away with you. ;-)
--
*I'm not as think as you drunk I am.

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To avoid the need for compressed air couldn't you use an electric drill nibbler attachment? eg: (Amazon.com product link shortened)
Alan
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On 2/5/2017 11:33 AM, Alan Dawes wrote:

Probably a bit fiddly compared with a purpose-built tool, whether manual or powered.
There are two sorts of devices described as nibbler
https://en.wikipedia.org/wiki/Nibbler
The "shears" type is OK for making a linear cut, the punch and die type which takes out a little rectangle at a time is best if you are cutting out "features" like a square recess or a T-feature.
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Anyone still have their Gosscut metal shears?
--
Tim Lamb

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