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Finishing plasma cut stainless steel

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locky_plasma
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Finishing plasma cut stainless steel

Postby locky_plasma » Fri Mar 15, 2013 6:05 am

Hi,

I have been asked to produce some brushed Stainless Steel letters for outdoor signage on a building. To date I have only plasma cut mild steel, although I`m sure the stainless won`t be a problem to cut once I get the parameters set, after some playing. Cutter is a miller spectrum 375 in a CNC table.

The question I have is how to achieve the brushed finish on the cut. I am assuming the parts will exhibit a small scorch area next to the cut, which will need to be buffed / polished back to match the original brushed finish. I am intending to use 316 stainless with brushed finish, although I am concerned that this appears to have a thin polycoating - how does this behave when plasma cut? I would be happy to start with another finish of sheet and then apply the brush finish, but would like some suggestions on how this might be achieved.

Assuming the sheet will be 2 or 3mm thick. I have access to a vibratory tub finisher.

Thanks in advance

Geoff

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Gamelord
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Re: Finishing plasma cut stainless steel

Postby Gamelord » Fri Mar 15, 2013 9:38 am

I cut a lot of stainless, mostly 3/16" & 1/4". The edges will be black from the cut and will need to be sanded before buffing. Also, the edges are not nearly as smooth after cutting as steel so again, sanding is a requirement. Thinner material may not be as bad but because of how hard stainless is, your best bet is to sand. I have also tried tumblers - had near zero results after tumbling for 2 days. Barely took off the mill scale. A flap disk is the easiest I have found thus far for flat surfaces. An expanding wheel on the grinder for the edges - get plenty of belts as stainless eats up the paper quite fast.

If you are using finished stainless the clean up may be a lot easier but you will still have to pay attention to the edges.

A good heavy duty grinder is your best bet. Someone posted a link to a tool that was similar to an angle grinder but had a large flap disk setup on it, like 5" wide. I am going to look into that because that may be perfect for sanding larger flat surfaces and getting a nice uniform sanding.

Sand blasting is also a good way to clean up the stainless before putting on the final brushed look.

Hope this helps.
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tdoe151
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Re: Finishing plasma cut stainless steel

Postby tdoe151 » Wed Jul 30, 2014 3:18 pm

I have made a few thing with brushed 16g stainless in the past few months. I use a dremel to grind inside the small areas and a quaternion flap disk for the outer edge. also for the burn area around the cut i use purple scotchbrite pads then i kinda blend the scoffs from that with the brushed pattern... it dulls the brushed look alittle bit but it is not to noticeable.{customers were happy with the look.PS i also follow the cutter and squeez water from a rag to cool the steel as it cuts...i think it helps with the burn and also helps with warping.
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motoguy
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Re: Finishing plasma cut stainless steel

Postby motoguy » Tue Jun 21, 2016 11:02 pm

I'll be cutting my first stainless job tomorrow or Thursday. Some 14" and 20" letters for a business. 20" will be mounted to the building exterior, 14" mounted inside, as "department" lettering. I've never cut stainless before, so I'm pretty nervous about it. 1/8" is what the customer wants. I'll be using 304. Customer is going with a "natural" finish (no polishing for me...they'll polish if they decide to go that way).

Looking into it, I already see that I underbid the job. I didn't realize stainless required the amount of post-cut cleanup mentioned above (grinding wheel for dross, the flap disk on large/smooth edges, die grinder on smaller interior edges, and buffing of the heat affected zone). Oh well, at least I'm getting paid something to learn. Next time I'll know, and I'll have most of a sheet of "free" .125 stainless to sell/cut to make up the lost $.

For this cut...I'm curious if there would be a preference for 45a shielded Hypertherm consumables, or Finecut? I don't think the narrow kerf width of the Finecut will be beneficial, but less angularity would. It's my understanding that the Finecuts offer less angularity. However, the 45a consumable will run .06 off the table (per book spec), whereas the Finecuts call for .02...which also makes me nervous.
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Gamelord
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Re: Finishing plasma cut stainless steel

Postby Gamelord » Wed Jun 22, 2016 4:19 pm

If you have excess metal, I would just run some smaller tests to see how it goes. Pick the one that looks best to you. It really does cut nice, personally I would use new consumables regardless of the condition of what you have on there. Change back to the ones you pull off for carbon steel if they are still good to go. Stainless is very prone to angularity if your consumables are the slightest bit warn. (at least that is what I have ran into). If set right, dross is not that bad, set wrong and you will have some nasty cleanup though. You always have the black burn on the edges though. 1/8" should be pretty easy to clean up though, flap disk and a few minutes on each letter should do it, dremel the hard to get inside cuts. I wouldn't worry about buffing the edges at all. If they are going to do the finishing then the hardened area next to the cuts should get cleaned off when they polish the rest of it so you may not have to worry about that either.

Let us know how it goes.
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motoguy
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Re: Finishing plasma cut stainless steel

Postby motoguy » Thu Jun 23, 2016 1:52 pm

I'm pleased to say it cut very, very well this morning. I ran the torch off the sheet on a letter, but that's user error. I'm ok with that...it's the "why the $&%^*% did it do that?" stuff that drives me nuts! Otherwise, the cut went flawlessly. I would say it cut better than most of the mild steel I've done...but I think that's because I've applied all the lessons learned on the mild steel! It was only last week that I finally found a combination of CV settings, drawing import settings, post-import node reduction, and cut rules/DTHC settings that really seem to "click" together. Hopefully the days of jagged cuts and running the torch into the metal are behind me!

I used the 45A nozzle, and all new consumables for the cut (shield, nozzle, electrode). I had to interpolate book specs for the 11 ga. I ended up using .06 kerf width, 120 ipm, .4 pierce delay, 133 volts. Raised my water level to ~1/2" below the sheet. Essentially no dross on the back. Really, none on the full-speed cut areas. Had small amounts of nastier stuff where my cut rules slowed to 40/60/80% in some of the tight curves/corners. I would not want to grind away large quantities of that stuff!

I hit all the edges (that I could reach) with my flap wheel/grinder. Going back over some of the interior cuts/corners with a dremel, will finish that after lunch

All in all, it cut way better, and cleanup is way faster than I anticipated. I'm pleasantly surprised. Now I just hope the customer decides he does NOT want standoffs...though I have a TIG in my garage, I've never TIG'd anything. I don't want these letters to be the first!
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kazlx
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Re: Finishing plasma cut stainless steel

Postby kazlx » Thu Oct 13, 2016 2:22 pm

I recently did a sign in 304. I prepped all the letters after cutting, welded standoffs on using a jig I made on my lathe and 1/8" 304 rod. I sandblasted everything and left the sides and back matte from the sandblasting and for the faces I used a belt sander and scotchbrite pad to finish.

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SeanP
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Re: Finishing plasma cut stainless steel

Postby SeanP » Thu Oct 13, 2016 4:23 pm

Nice work, sign looks great and I like your welding jig, must make one up!
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kazlx
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Re: Finishing plasma cut stainless steel

Postby kazlx » Thu Oct 13, 2016 4:31 pm

Thanks. With the 304, it's really quick and you don't even need to use filler. Just a quick, hot blast on the base metal and the post will drop in a little. Took me a few practice shots to get the technique down, but it went pretty quick and worked out great.

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SeanP
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Re: Finishing plasma cut stainless steel

Postby SeanP » Thu Oct 13, 2016 6:17 pm

kazlx wrote:Thanks. With the 304, it's really quick and you don't even need to use filler. Just a quick, hot blast on the base metal and the post will drop in a little. Took me a few practice shots to get the technique down, but it went pretty quick and worked out great.


And thankyou! that's another added bonus, nice one.
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