# cut a rectangular window in a thick steel sheet?



## Florin Andrei (Jan 6, 2015)

(I've access to a mini-lathe, mini-mill, and various hand tools.)

A square-ish piece of stainless steel, 2 mm thick, size about half a page. I need to cut a rectangular "window" in the middle of it - an LCD display will be fitted into that slot. The size of the display is about 70 x 16 mm.

One thing I could think of, and it would definitely work, is to use the machine and cut a slot with rounded corners. I've a 20-piece end mill set, 2- and 4-flutes, of various sizes. I could use one of the small mills, to minimize the radius of the corners.

Then grab a file and "sharpen" the corners until they're square.  But it's going to be a slow process and probably won't look that great in the end.

Could anyone suggest a better idea? Thanks.


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## Bill C. (Jan 6, 2015)

Florin Andrei said:


> (I've access to a mini-lathe, mini-mill, and various hand tools.)
> 
> A square-ish piece of stainless steel, 2 mm thick, size about half a page. I need to cut a rectangular "window" in the middle of it - an LCD display will be fitted into that slot. The size of the display is about 70 x 16 mm.
> 
> ...



That will work.  Put a piece of plywood under it and clamp it down.  Use a 1/2" center cutting end-mill to rough out the opening.  Then use the smallest end-mill to clean up the inside perimeter. File the edges to remove sharp burrs.


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## countryguy (Jan 6, 2015)

Of course a flame head would tell ya to pop that onto the Plasma table.     I'm looking forward to learning to use a Mill to do this!  But the Plasma table is sooooo neat!  
JEff /CG


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## george wilson (Jan 6, 2015)

I advise that a 1/2" end mill may be too much for a mini mill to handle,though I have never used a mini mill. I'd use a 1/4" end mill and use the slowest possible RPM on it. Stainless will eat up your end mill if you try to cut it too fast.


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## 12bolts (Jan 6, 2015)

Good advice from George.
Drill the 4 corners (say 10 mm ish) first to give you a start hole, then mill the window out with your 1/4 end mill. Sharpen up your corners with a small endmill or file. Nice and slow RPM's, lots of dark oil, dont let the end mill rub the work.
Would expect there to be a fascia or euscutcheon on the display to cover the hole surrounds anyway?

Cheers Phil


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## DMS (Jan 7, 2015)

I agree with George, get a couple 1/4" (or 6mm) 4 flute carbide end mills. When I had my sx2, I tried to stay around 3/8" on steel, but never cut stainless on that little guy. Filing would not take long. With some care you could make it look quite good.


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## Florin Andrei (Jan 7, 2015)

Plasma would be neat, but I don't own a plasma cutter and I try to do as much as possible with my own tools and machines. This is as much a learning exercise as trying to actually finish the project.

I'll use a small-ish mill and slow speed. I've noticed already that SS is hard on drill bits, I assume it can't be too gentle on mills either.

"lots of dark oil" - does that mean I need to drip some oil ahead of the mill? Do I really need a lot, or would a few drops suffice? I assume this is for cooling. (remember, I'm new to this thing)

"dont let the end mill rub the work" - what does that mean?

The display doesn't have any kind of nice frame. I'm already thinking to try and round the corners a little on the display, maybe 1 mm or so, but I should probably banish that thought. Anyway, this is the display (OLED, not LCD, but same function). You can't see very well in that dark picture but the corners are not rounded at all - they're exactly square.

http://www.adafruit.com/products/823

It's a nice display, I'll try and do a good job with the faceplate.


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## 12bolts (Jan 7, 2015)

Florin Andrei said:


> "lots of dark oil" - does that mean I need to drip some oil ahead of the mill? Do I really need a lot, or would a few drops suffice? I assume this is for cooling. (remember, I'm new to this thing)"


Dark, (sulphorus) oil for cutting, lubricating capabilities, (no need to drown the work, my poor phrasing :whiteflag: )



Florin Andrei said:


> dont let the end mill rub the work - what does that mean?


SS work hardens easily and quickly. Make sure the tool is always cutting, (steady pressure), dont let it dwell and rub on the work. Slow RPM and steady constant feed rate.



Florin Andrei said:


> The display doesn't have any kind of nice frame.


Could you cut a neat plastic euscutcheon to suit?

Cheers Phil


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## uncle harry (Jan 7, 2015)

I often drill a series of closely spaced holes slightly away from the final desired opening. This reduces the tool forces on the cutter used to clean up the opening. This approach reduces the clamp-down pressure required to hold the thin metal.




Florin Andrei said:


> (I've access to a mini-lathe, mini-mill, and various hand tools.)
> 
> A square-ish piece of stainless steel, 2 mm thick, size about half a page. I need to cut a rectangular "window" in the middle of it - an LCD display will be fitted into that slot. The size of the display is about 70 x 16 mm.
> 
> ...


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## george wilson (Jan 7, 2015)

I should have been more thorough with my post above. Yes,keep the work moving. Do not let the cutter stay(dwell) in 1 spot,or the stainless will harden. Carbide is good. Dark cutting oil is also good.

Try a cutter much larger and your mini mill will probably shake itself to pieces.

I haven't had a mini mill,but I did own an Atlas as my first mill. It cut brass o.k.,but steel was always a bother with a cutter of much size at all. And,I'll bet it was heavier built than a mini mill.


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## Frank Ford (Jan 7, 2015)

uncle harry said:


> I often drill a series of closely spaced holes slightly away from the final desired opening. This reduces the tool forces on the cutter used to clean up the opening. This approach reduces the clamp-down pressure required to hold the thin metal.



Absolutely!  I'd "chain drill" it without a second thought, especially if it were a bigger hole. 

 Usually, for tough stuff, I'll chain drill on the mill, take it off, and chew out the pieces between the holes by plunging or whatever with an old, dead end mill I save for that kind of destruction derby.  Or, I'll drill the holes, take the part off the mill, break out some bits and feed a hacksaw blade through it, and cut the piece out by hand before sticking it back on the mill for finishing the cut.


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## epanzella (Jan 7, 2015)

As a "no mill/no plasma cutter" guy I would scribe a line and cut it out with a cutoff wheel in a 4 inch angle grinder. The short part of the rectangle would have to be grooved short, broken and filed due to the radius of the wheel if you don't have a cutoff tool for your dremel. But, I do.


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## grandpaswagon (Jan 7, 2015)

Have you considered using a Dremel and a very small cutoff wheel to square up the corners have to you drill/mill out the opening?

Should be easy to control and wouldn't take much time.  Should get results similar or better than a manual file.


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## Dave Smith (Jan 7, 2015)

epanzella said:


> As a "no mill/no plasma cutter" guy I would scribe a line and cut it out with a cutoff wheel in a 4 inch angle grinder. The short part of the rectangle would have to be grooved short, broken and filed due to the radius of the wheel if you don't have a cutoff tool for your dremel. But, I do.



my way also----I always keep a very thin cutoff disk in my dremmel type grinder and in my air angle die grinder and it doesn't matter how tough the stainless is--it zips right through it----the more you use the tool for cutting by hand--the better you get---the thinner the blade the quicker and nicer it cuts---if you are handy with them--you can cut the corners perfectly square----clamp your piece down first so you can control the grinder with both hands----Dave


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## Florin Andrei (Jan 11, 2015)

If I use a thin mill, what would be the smallest diameter that would make sense?

I've seen some very thin square end mills out there, like 1/64", but I can't possibly imagine what those are for. Is anything thinner than 1/8" useful for a straight cut like this?


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