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Old 16-03-2009, 16:16   #1
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Bending and Welding Stainless Tubing

Hello, I have designed several projects for our boat out of stainless tubing. A small arch for our radar and antennas, and a bit larger bow pulpit with a seat, modidied life lines aft, etc...
While I do have experience bending and welding steel tubing (my son and I used to fabricate and modify Jeeps), I haven't done this with stainless yet. I have a wire feed welder (MIG), and a hydraulic bender. I am however, unfamiliar with the bending and welding charactoristics of stainless.
I would appreciate hearing from anyone who has worked with stainless tubing and fabricated boat parts with it.

Thanks! Bob
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Old 16-03-2009, 16:35   #2
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Most of the stainless welded on boats is TIG welded for beauty. The tubing will probably work harden a little faster when bending than mild steel.. so allow a little extra springback. put the weld in the tubing on the neutral axis of the bend. (ninety degrees to the outside or inside of the bend)
I believe it is preferable to use 321 SS weld wire which helps to discourage the liklihood of rusting in the weld and heat affected zone. There are some other wires too... 347? 309L? something like that.
If you can get the pieces bent up, it might be worth your while to find someone on the Seattle side to just weld it up for you.... a lot of good aircraft welders who moonight out of their garages.
I might be able to find you someone, it's been a while but have some contacts....
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Old 16-03-2009, 16:37   #3
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Also, forgot to mention... If you can find a railmaker who will electropolish it after welding it will keep it from rusting.....
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Old 16-03-2009, 16:45   #4
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stainless tubing

Well, it sounds like you already know how to bend it, and I don't think you'll find that part of it that much different from bending steel tube, except you may be working with different tubing diameters, and different wall thicknesses. Play around some, and you'll figure out how to bend it. It's stiffer. Heavier wall (.090" and up) is easier to weld but harder to bend.

You'll need a way to fishmouth the ends of the tubes... a bridgeport is best for this, but it can be done carefully with an angle grinder, then a small belt sander.

I don't think you'll be happy with a MIG... TIG is much better for stainless which will be visible, but TIG needs a good fit up, because you can't easily fill much with it. Use 308 wire for 304, but it (the 304) will discolor and stain some. You're better off with pre polished 316 tube and 316 wire. Then you just have to take care not to scratch it while bending and fitting, and polish the welds.

Best, Bob S/V Restless
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Old 16-03-2009, 16:50   #5
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Bob,

I would not disagree with Cheeckako at all but what is it you need to make?

Sometimes the details matter. I had some TIG work done on a custom two part hinge for w heavy duty swim platform that hinges on the transom. The guy that did it knew what he was doing. I would also agree in WA you have access to some folks that have done a whole lot of this high tech stuff. Making friends has rewards.

My neighbor down the street has a Newport 33. He had a 27 and I've sailed a 30. We had a guy stop buy our dock that was doing a circumnavigation in a 27 but he only got from Baltimore to Australia and decided it was too small. He wound up getting married. So proves the theory of relativity - your wife knows when the boat is too small. They may not be fancy boats but you still find a lot of them out there showing up in all kinds of places.
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Old 16-03-2009, 17:24   #6
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I also see the good stainless shops brush that powder-like acid on the weld shortly after welding, have it do it's work and then rinse with lots of water. Must be a passivating step. Any discoloration disappears with that too.

cheers
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Old 16-03-2009, 17:30   #7
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S/S tubing source

I did what you are planning to do. First go to Railmakers in Everett WA. They ship in the only last remaining quality S/S tubing (From Georgia, I believe). The owner was quite helpful and sold me the tubing making recommendations that were good. All the rest of the stainless tubing is from China and does not yield the quality for good marine applications.

Made a huge radar arch, mast safety rails and boom gallows. I learned how to do my own "electropolishing" using a current limited 24V power supply and citric acid. Learned how to use 3M pads with an air polisher to grind down and polish all the welds before electropolishing. Finall used various compounds to get that mirror finish. Lot of work but I guess it was worth it.

Using 1.25" and 1" tubing recommended by Railmakers I noticed about 7 degrees or more of springback from a 90 deg bend. Went about it gradually to discover repeatability. Used a drillpress mounted fixture with a Lennox metal hole cutter to make the various holes necessary to join the tubing at various angles required. Used a fairly slow speed on the drill press (around 80rpm) and lots of cutting oil to make the cuts. I forgot the name of the fixture but bought it online for not much $. Believe it or not stainless is very soft to cut you just have to use the correct feed speed and spindle speed to correctly load the cutter and the stainless cuts like butter. If you don't use the correct speed and load the stainless will work harden and the cutting edge will not bite in.
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Old 16-03-2009, 18:55   #8
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Thanks for all the information. I am making a radar arch, a swim platform (frame), and a larger bow pulpit. To start.
I'll contact Railmakers and check into materials. I figured I wasn't the first guy to weld up some SS for his boat!
I work at a boatyard here in PT and have access to heavy duty grinding and polishing equipment.
Thanks again!

Bob
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Old 17-03-2009, 02:30   #9
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Quote:
Originally Posted by s/v Jedi View Post
I also see the good stainless shops brush that powder-like acid on the weld shortly after welding, have it do it's work and then rinse with lots of water. Must be a passivating step. Any discoloration disappears with that too.

cheers
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I am not sure what process you saw but around here they best guys using a "pickling paste" that is extremely toxic and is very difficult to obtain outside the "inner circle". Among other things, it contains the very toxic hydrofluoric acid. See Hydrofluoric acid - Wikipedia, the free encyclopedia
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Old 17-03-2009, 10:58   #10
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Wotname: that's it but I saw it in powder-form too, becoming a paste when applied with wet brush!

cheers,
Nick.
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Old 17-03-2009, 12:20   #11
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Bob, the pickling (passivating) paste or dip is essential. If your benders use tool steel (carbon steel) they will leave fine fragments of it in the stainless, so anywhere the stainless has been worked it is liable to rust afterwards unless you passivate it. If you can do the fab work, and find a local shop to dip it and passivate it afterwards, that may be the best compromise for you, instead of playing with acids.
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Old 18-01-2010, 06:45   #12
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This may be a bit off the specific topic, but has anyone built an arch/pulpit using mild steel or aluminum and then powdercoating it? I don't feel every bit of railing or fitting needs to be stainless-shiny (I'm thinking white or light gray like my boat) and stainless-expensive.
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Old 18-01-2010, 06:51   #13
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Just remember that powder coating is quite porous in comparison to say epoxy paint.
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Old 18-01-2010, 07:18   #14
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You can buy the drillpress attatchment for cutting the tubing ends with a hole saw from Harbor Freight.I would do the fabricating and tack it together with your mig and then take it somewhere to have it tig welded, i use a local sheetmetal shop who do beautiful welds.
Anzo,i agree,not everything needs to be stainless,one of the nice things is that aluminum is 1/3rd the weight of SS so you can go with larger diameter tubing and have a more rigid structure and still be lighter.
Steve.
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Old 08-06-2010, 04:38   #15
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3 inch pulpit plates?

I am makeing grabrails and pulpit for my boat. Who supplies premade 3 inch round pulpit plates for welding. I see plenty of socket style but I just need the flat plate so I can make difrent angles. I could use 2 dozen plates 3 inch round and 3/16 thick to weld tubing to. Preferable these plates would have 3 holes pre-drilled for 1/4 20 flat head screws. If i had to I could use square or rectangular plates but round are what i realy want/need.

btw. I would like to see some pictures of your project.
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