Cutting stainless

[neitzel]

Here's a question for the fabricators.
I have to cut a large hole (2'x3') in a stainless steel box. It will be in the door a of an instrumentation box for a window. The stainless is pretty heavy, maybe 14 gauge. The cut will be visible when the door is open.
How can I make a nice clean, straight cut on this?
I have access to a plasma cutter, but I'm worried the heat may discolor the material.
I worry that free handing a cutoff wheel on a grinder or or die grinder will not be straight enough.
Are their any other options that I'm not thinking of?

Thanks

 

[Grinder Bill]

A fine grit flap wheel will polish out the discoloration from plasma cutting; just keep the heat down.

You could also rent a metal cutting circular saw.
http://www.mytoolstore.com/milwauke/6370-21.html

 

[garfunkle24]

Why not just use the cut-off wheel and a chunk of angle iron or whatever you have as a straightedge to cut against?

 

[pirana]

Will the corners be rounded or square?

 

[APEowner]

I'd use the plasma cutter with a straight edge guide and polish out the discoloration.

 

[neitzel]

Why not just use the cut-off wheel and a chunk of angle iron or whatever you have as a straightedge to cut against?

Run a guard against the angle?

Will the corners be rounded or square?

Square. Round would work as long as the radius is 3/4" or less.

 

[neitzel]

I'd use the plasma cutter with a straight edge guide and polish out the discoloration.

How far into the stainless do you think would discolor? Their will be a frame that covers the window and extends 1/2" - 3/4" beyond.

 

[Frank The Plumber]

The plasma cutter is your best bet, put a straight edge and use it as a guide. I have used a wet saw with diamond blade, no marks.

 

[garfunkle24]

How far into the stainless do you think would discolor? Their will be a frame that covers the window and extends 1/2" - 3/4" beyond.

Not at all if you use a cut-off wheel......

 

[metal1313]

i dont have a suggestion really, but i have a question, how would a good jigsaw and proper blades be for cutting some stainless

 

[REAL HOT SCHITT]

Hi from new zealand.
I cannot nut out the hole size, but try sumfink like a "sink punch" or a carbided tipped "blue mol" or "starrett" hole cutter on drill.

Cut on low to med revs and hold real stedy to stop chatter and use water for cooling.

Do not use plasma as heat will distort metal, also brush on passivating paste (from welding gear suppliers)to clean off oxides...note; do not sniff fumes as it can lead to blindness or death. Also the acid will eat clothing.

After paste....rinse with soapy water and fine sand then polish to soot.

OH! USE THE HOLE SAW TO CUT RADIUS CORNERS AND FINE JIG-SAW FOR ST8T LINES.
IF FERROUS TOOLS COME IN CONTACT WITH STAINLESS IT WILL RUST UNLESS ITS GRADE 316 OR 316L...HOWEVER THE PASTE WILL NEUTRALISE IRON OF TOOLS.

15 YEAR STAINLESS WELDER.

 

[garfunkle24]

Run a guard against the angle?

Just hold the grinder vertically as if making a plunge cut (if workpiece is flat) and let the flat disk side run along the guide piece as you cut.

Due to the frame it doesn't really matter in this application, but you want to go slow into the corners so as not to overcut and leave an ugly notch.

Plasmas are nice for cutting shapes or cutting in bulk but I much prefer a grinder with cut-off wheel for straight cuts in general. Minimal deburring etc required.

i dont have a suggestion really, but i have a question, how would a good jigsaw and proper blades be for cutting some stainless

A cut-off wheel has a tendency to stay straight by following it's own groove. While a jigsaw would work, it is designed to do the exact opposite.

NB If you do use any kind of abrasive, use new stuff if possible or at least nothing used on ferrous metals. It is possible to contaminate the stainless workpiece and compromise it's anti-corrosive properties.

 

[bobadame]

10' of cut length, plasma torch for sure. Discoloration is easy to remove with Scotchbrite.

 

[Frank The Plumber]

i dont have a suggestion really, but i have a question, how would a good jigsaw and proper blades be for cutting some stainless

Really depends upon which grade of stainless, how thick etc, would not say it couldn't just that it may make a mess of it, There are a couple of new diamond sawzall blades that will do small amounts. They don't really last all that well on SS.

 

[gordsgarage]

My technique of choice is the plasma with a straight edge. Before I cut though I drill 4 holes presicly in each corner. This way it already sets me up for a square cut and it also gives my a nice radius on each corner. When I clamp my staight edge for the cut I ensure the staight edge is on my "good" piece, in other words, if I slip with the plasma I will only gouge into my scrap piece. Discoloration can be taken out with a flap wheel or Scotch Brite.

Gord

 

[garfunkle24]

To the OP: Do you have a plasma cutter or access to one, including compressed air etc?

If not, and you're not looking for an excuse to buy one, it becomes a very easy choice.
I assume that you have some kind of grinder you can attach a cut-off wheel to?

 

[neitzel]

To the OP: Do you have a plasma cutter or access to one, including compressed air etc?

If not, and you're not looking for an excuse to buy one, it becomes a very easy choice.
I assume that you have some kind of grinder you can attach a cut-off wheel to?

Yes, the plasma cutter and grinder are both in the shop.
I guess I need to try them both on some scrap to see what the results are.

 

[metal1313]

the stuff i have to cut is pretty thin, and bonded to wood, and since i dont have a plasma nor the funds to get one, jig saw it is. its a tiny hole anyways, just over 4ft of run.

 

[APEowner]

How far into the stainless do you think would discolor? Their will be a frame that covers the window and extends 1/2" - 3/4" beyond.

Probably not even 1/4" beyond the edge. You might get more discoloration with a cutoff wheel than you would with the plasma cutter. Since stainless has a tenancy to work harden cutting with a blade of any sort can be problematic. On mild steel I'd encourage the idea of using a hole saw to do the corners but stainless is quite sensitive to speeds and feeds so unless you can get it in a mill or a drill press where you can run the cutter slowly and provide the high cutting pressure I wouldn't bother.

 

[EdT]

I'm a big fan of trying out a new technique on something that doesn't matter before I commit to using it on the real deal. In this situation, you have six square feet of what is probably scrap at the end of the job so you could test a couple of techniques in the area that will be scrap before you do the cuts "for real".

 

[garfunkle24]

^^^Very smart advice.

 

[Vicegrip]

Good advice. Always test a method on a scrap or portion that will be a drop. I have plasma, cut off wheel loaded angle grinders and a metal saw. I use the cutoff wheels with a guide. SS is hard on the saw blade. Done right the cut off wheel can make clean sharp cuts. Guide goes on the "keep" side to protect from slips. Hold very lightly against the guide and try and cut a groove without breaking through until foil thin. Plunging through and then cutting shortens the wheel life dramatically I like to slide the wheel lightly along the guide and steel making a light groove and only after it forms put any pressure on the wheel. back and forth moving carefully but quickly not lingering. long ever deepening groove until almost through. If it is bisection rather than an L cut I stop just shy of through and bend the drop off the keep then dress off any flash with the wheel or gently with a flap wheel.

 

[Vicegrip]

the stuff i have to cut is pretty thin, and bonded to wood, and since i dont have a plasma nor the funds to get one, jig saw it is. its a tiny hole anyways, just over 4ft of run.

Plasma only cuts through metal. Metal on wood would be a mess. Stainless will eat jigsaw blades if it gets hot. It does not spread heat like carbon steel and work hardens quickly. This leads to dull burnt blue cutting tools real quick. Once a heated and hardened area forms it will dull a new even cold blade. Go very slow as in slow blade speeds and use some form of coolant. Even regular water works fine. Something as simple as another person with a spray bottle set on stream keeping the blade and cutting area soaking wet.

I myself have not had much luck with SS and jig saws. The blade speeds are high and blades go dull. Up cut blade and wood bonded thin metal might have ragged edge issues from the metal pulling up. A second shoe on the saw bottom with just a slot for the blade to move through helps. dirty trick, grind the jig saw blade to flip and fit as a down cut. i have a clamp type jig saw and use down cut blades for super fine no tears cuts. Have to go light feed rate as the saw wants to come up on the cutting stroke.

 

[steel 35]

If you want a radius, Electricians have knockouts if you have them use them for the corners then take your pick, plasma or cut offs either one works great just don't spray the arc of the plasma onto other surfaces, it doesn't clean up so well. I drop the cutoff wheels through then pull toward me and use the disk for a straight edge following a scribed line. Jig saw just take the blades out of the package and through them away it will save you a lot of grief

 

[mjb]

How far into the stainless do you think would discolor? Their will be a frame that covers the window and extends 1/2" - 3/4" beyond.

I was using my plasma cutter today and remembered this thread. I had a piece of stainless drop and figured I could take some pics of the discoloring.

Stainless

Straight edge clamped on

Fresh cut

I cleaned up the edge, but did not polish out the discolored area.

The heat affected zone is very small.

Good luck!

 

[neitzel]

I was using my plasma cutter today and remembered this thread. I had a piece of stainless drop and figured I could take some pics of the discoloring.

[Snip] [\Snip]

Good luck!

That should do well for the project I'm working on. I intend to make some cuts over the weekend while at work. I'll try to remember to take some pics.

Thanks for the examples