Machining question, how to make a 3" hole in SS

snipped-for-privacy@hotmail.com (Carlos) wrote in news: snipped-for-privacy@posting.google.com:

There is *NOTHING* easy about doing anything to 304 SS. It work hardens as you attempt to machine it. It dulls cutting edges very quickly. You could try a standard hole-saw, but about 1/8" into it, it will work harden and you'll be producing only smoke and an ever increasingly hot and very dull hole saw. SS is just nasty to machine, and is the reason the shop gave you the quote they did. Tools are expensive, as is resharpening time, and you can't machine it fast. It will be expensive, and some shops would just as soon you take SS jobs elsewhere.

Hi Carlos:

I would suggest that you simply have it NC machined with an ordinary end mill. We do it all the time; it's a piece of cake. Maybe the machinist was just too busy to fit it in (or doesn't have NC). Stainless steel is a little harder to work with than plain carbon steel, but people drill it, tap it, machine it and saw it every day. #304 stainless is a very common alloy.

Another option is using a trapanning cutter, but that takes a special bit. They can also be wire EDM'ed or laser cut. I don't know how accurate the holes need to be--can you use a plasma cutter?

Don

Dear Carlos:

There is fellow in my community that cuts all kinds of shapes into 1/4"

304SS plate. He uses a water knife, driven by a CNC. Perhaps you could "rethink" your design into using a sandwich of thinner plates? Plasma cutters can do thinner stuff. I'm not sure how thick either a water knife of a plasma cutter will go...

How smooth do the edges have to be, and can you grind it there?

David A. Smith

Plasma jet or water jet. The first is widely found

Oxy cutter if a ragged edge is OK

Brian.

OP stated >>

I want to make 3 circular holes of ~3" in a piece of SS 304, 3/4" thick (maybe

1/2" thick).

Perhaps if OP backs up & lets us know what he's trying accomplish we could help him achieve his real goal.

with the goal in mind perhaps an material or process change to get the job done for a lot fewer $'s

Bob

While I agree totaly with the above comments, I f a rough hole is all that's needed and the pice can be positioned in a drill, then a maximum speed at 3" for a hole saw of about 120 rpm, useing cutting compound, and once started frequently lifting the saw and blowing the grove clear with an air line will get you through a 1/2" plate in about 15 minuets per hole. Junk a saw after it's done two holes.

Jonathan

Barnes's theorem; for every foolproof device there is a fool greater than the proof.

Thanks to everybody for your answers. The edge on two of the holes should be smooth for I was going to weld 2 flanges there. The other hole's edge is not critical. The machinist mention using NC milling to get the holes done, it might be piece of cake to do but he said it was going to take the whole day to make the holes. It needs to be one piece as opposed to several layers. I don't have plasma or water cutters. I didn't even knew water cutters existed :) Thanks to everybody for the ideas. I am thinking about what I will do.

Carlos H.

But the heat would adversely affect the corrosion resistance in the area. And that must be somewhat important or stainless steel wouldn't be used.

Welding can hurt the corrosion resistance in the area. Check into it...

Nonsense. Stainless steel is routinely welded all the time. Since it is often used in sanitary applications, welding is preferred to most other forms of joining since it provides a clean, continuous joint without leaving small crannies for contaminants to collect in. Incidentally, it is one of the easiest and cleanest materials there is to weld.

If you couldn't get stainless steel hot, what the hell *could* you do with it? Cut it with school scissors and paste it together?

Don

Nowhere did I say SS could not be welded. Nice strawman...

Suggest you read up on "carbide precipitation".

Ned Simmons

We haven't even begun to exhaust the possibilities yet (Though thanks to a writer of a private note for reminding me that hi chrome makes regular oxy-cutting a non-starter - The chrome oxide is refractory)

There's EDM and abrasive wire saw and abrasive disk and abrasive fluid and ....

Brian W

Welding can give a corrosion prone zone. Acid passivation is the routine response.

Brian W

Oh OK. I thought there'd be a remedy. Thanks.

...And I suggest you listen to someone who actually has experience with it. OK, let's get back to the real world here, kids. I've been designing stainless steel machinery and equipment for eighteen years now and in many different industries. Stainless steel is a very common material and has been around for years. It is not titanium and it is not exotic. It's used in the food industry, medicine, laboratory equipment and a lot of other places. You can machine it, tap it, weld it, form it, punch it and generally treat it like you do ordinary steel. Sure, it's a little harder to work with, but it's no big deal. The welds don't fall apart and rust; your milling cutters aren't ruined after one job.

I headed a research project on the effects of long-term exposures to high temperature of stainless steels in 1990 when I was working for Hussmann Industries. Some stainless steels, when held at high temperatures (greater than 800 F) for long periods (eight hour daily shifts for many months) and exposed to chlorine-based solvents can exibit intergranular corrosion over time. It can eventually lead to microscopic cracks and, over a long period, even leakage. Our equipment was made from thin sheet metal and could be theoretically exposed to such high temperatures if operated improperly. We switched to the lower-carbon #304L stainless steel to remedy the problem.

But again, let's get back to the real world. Unless you have some super-critical design that involves high temperatures, caustic conditions and extreme physical stresses, you simply don't need to worry about this scenario. The fact of the matter is that nearly all stainless steel is being welded and cut by the tons every day and has been for decades. And the world is not coming apart at the seams because of it. Most of it isn't even passivated.

All this poor guy wants to do is cut three simple holes in a slab of stainless for crying out loud.

Don

The observation of "carbide precipitation" is correct. Passivation is simply a surface treatment that makes corrosion attack on that surface less likely. Passivation can be accomplished by use of a non-ferrous abrasive, or an acid (not including chlorine or sulfur-based acids), and other chemicals/systems as well. If the entire surface is later attacked to remove this protective patina of "depleted free iron", the weld area will most commonly be found to be *the* most-corroded, and the first to be holed-through.

If you touch an otherwise passivated stainless steel surface with a steel tool, the stainless will start to rust. If you have a tank that is used to contain water, and a "little too much" ferric chloride is being applied upstream of this tank (a flocculation aid), all the passivation in the world won't help the welds survive.

All systems require maintenance.

David A. Smith

Dear Don Gilmore:

Passivation can be performed by abrading the surface with a non-ferrous abrasive. Grinding wheel, Scotch-brite, clean sandpaper, clean sand (not used for blasting steel parts), stuff like that. The trick is just to be sure all the exposed surfaces are so treated.

Agreed. He might need to know, but not worry, about this erudite stuff.

David A. Smith

As a rule I pay more attention to folks who offer helpful and accurate advice as opposed to trying to impress with their c.v. But since you seem to put some credence in that sort of thing, I was ending my involvement with a SS fabrication business I founded around the time you started in the field. These days I spend most of my time designing machinery for processing and fabricating refractory metals where very high temperatures are the norm.

No argument there.

The published data of the AISI puts the time for the onset of sensitization of 304 at around 1 minute @ 800F. Precipitation is detectable in the L grades in 10 to 100 hrs.

While I agree it's unusual, I have seen failures of weldments in marine environments where there were no elevated temps involved other than the original welding.

Leave out "super-critical" and replace the "and" with "or" and I'll agree. But the existence of several non-obvious failure mechanisms for SS is not, as you put it, "nonsense" -- ignore them at your peril. Ned Simmons