Bending Stainless Tubing

[Jon A]

Greetings All, I am finishing up on a two year build of John Atkin's Ninigret. One of the last projects is to fashion a canopy to shade our elderly and already sun damaged skin from the sun. My question is; does anyone have experience bending thin wall 7/8" stainless pipe? Can it be done with a conventional electricians conduit bender? All my bends would be less than 90 deg so the pipe would not be tortured too much and if I could set myself up to do the bends myself, I could design things right on the boat and get the angles looking like this thing belongs. The boat is drop dead gorgeous (thank-you Mr Atkin) and I need a canopy that works but doesn't take too much away from the looks. Any input would be appreciated.

Thanks,
Jon

[AndanteEd]

First fill the pipes with tightly packed sand.

These chaps seem to make it work:

[stromborg]

Bending pipe is tough and is as much as art as science. You'll want tooling to match the pipe, the conduit bender electricians use might work but the galvanized mild steel they use is softer than stainless. Calculating the "before' and "after" lengths will take some practice, you don't want to waste a bunch of expensive tubing trimming everything to length nor do you want to come up short and have to start over.

Best of luck, pictures as you go would be nice.

It might be most economical to hire this part out, and I don't say that very often.

[jpatrick]

I believe that pre-bent tube can be purchased from various suppliers. Sail Rite is among them.

At one time I did a fair bit of emt bending for an electrical install. It takes practice to get the fits just right. Stainless tube would put up a pretty good fight.

Jeff

[coelcanth]

i've done Cro-Mo but not stainless..
more wall thickness will reduce the chance of crimping the tubing, but also be harder to bend.
i think you have a chance, but it might take some upgraded tooling.
the best conduit benders for kink-free bends are the ratcheting types with a following mandrel that cradles the tube on both sides.
https://www.zoro.com/ridgid-tube-ben...78/i/G3048202/

packing (tightly!) with sand and using heat is another option.
also, there is a low melting temp bending filler called Cerrobend that might be superior to sand.. i have no experience with those

[Canoeyawl]

It is not uncommon to just tig weld pre-made mandrel bends...
see: http://www.mandrelbends.com/mandrel-bends.html

[Peerie Maa]

It's a wooden boat, I would steam bend ash or oak. Much more salty.

[rgthom]

I remember bending steel tubing in high school shop, making go-karts and minibikes. We packed with sand and heated with a torch.

For wooden boat biminis and tents I make the supports from laminated wooden arches, cotton phenolic tubes, wooden dowels, and bimini fittings.

[the_gr8t_waldo]

conduit and pipe are measured by their inside dia., tubbing by it's outside. It dosen't take, much of a miss match, before your turning out "scrap". I've got a few miles of installed conduit in my resume... and wouldn't suggest, using an electricains hand/power bender, unless if you have a hight tollarence for fustration.

[hawkeye54]

Does anyone know if a local automotive muffler / exhaust system shop is equipped to bend tubing of that size ? I work at a 'Big-Box' store, and if I recall, we only have manual tubing benders in sizes 1/2", 3/4", and 1" . . . .



Rick

[Slacko]

I've bent a few Km's of 316L stainless small tube, 1/2" being the largest.
This was heavy wall for high pressure, no sand fill or heat, just Swagelok branded benders.
As said above, you must have the right bender for the tube or pipe you are bending.
Quality benders are marked for calculating the length of the finished pipe.

[Arlc]

I once had a welder bend some stainless tubing to make a shower rod to enclose a hot tub for a house I was building. I remember he slid another piece of tubing into where he calculated the 90 degree bends to be then used a torch and very large bending machine.
Not. something I would try at home.

[David G]

Every hobbyist or small boatbuilder I've seen try to bend stainless - even if they've experience bending other tubing - has failed. Personally - I don't need it often enough to gear up and ride the learning curve. So I just farm it out to a local artisan.

[Canoeyawl]

You can learn more about mandrel bending here: https://www.tubeformsolutions.com/bl...el-bend-a-pipe

[Jon A]

Well, Thanks all for stopping me from heading down a road that would not work. Stainless is out!!! But I still want to do this myself and my next question would be how about a frame in copper. Type K 3/4" copper tubing is relatively thick walled and is readily available and will bend easily and should be stiff enough for this. Connections could be brazed for strength. Might turn green and stain the canvas but maybe a coat of paint would help. My Ninigret is not fancy, no varnish, what they call workboat finish.
Any thoughts?

Jon

[Paul Schweiss]

The real pros bending stainless have a mandrel bender that is matched to the tubing to prevent collapse and scratching of nice polished SS. These are expensive machines, as an apprentice we did the packed sand routine, but this was a fairly gentle long bend and we had lots of hands to spread the load and do a bit of overbending so it matched the curve of the deck.
Try talking with the canvas shops, they either own a mandrel machine or job it out to someone. They can give you the minimum bend radius for your tube size and wall thickness.

[sp_clark]

...how about a frame in copper. Type K 3/4" copper tubing is relatively thick walled and is readily available and will bend easily and should be stiff enough for this.

My experience would lead me to think copper's gonna be too soft for this purpose. One good, hard blow may very well fold your canopy's frame in half in the blink of an eye.

Were I in your position I'd give a thought to how some modern bicycle frames are being made of wood these days, certainly strong enough for that application!

https://sojourn-cyclery.com/bikes/ https://connorcycles.com/

https://www.montaukhardwoodbikes.com/ https://www.htechbikes.com/wooden-bikes

https://www.puretimber.com/renovo-bikes/

And trust Nick (post #7 above) to give good advice for this.

[Dave Lesser]

You might consider red brass (alloy 230, 85% Cu, 15% Zn)

https://www.onlinemetals.com/en/product-guide/alloy/230

[sp_clark]

Red brass would be a fine substitute for SS or copper tubing. You'd want it annealed for bending, or if hard-drawn for any straight sections, that can be annealed where bends are planned.

More easily worked than SS, more durable than copper and easily brazed for connections.

[Andrew2]

Since I am a bit of a DIY tool (fill in your fav nut flavour) I made a draw bender for 3/4" and 1" ss tube. It makes nice curves up tp 90°. But, take the advice to either farm it out or buy bends and weld them into the frame. So much easier. Conduit pipe benders are not up to it , nor are the hydraulic ones that push it between two curved 'pins' Known as 'kinkers' for good reason. They work with thicker walled pipe, but not thinner stuff.

[JimConlin]

The cost of red brass and bronze pipe will be exciting.