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25-06-2022, 01:01
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#1
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Registered User
Join Date: Sep 2008
Location: On the boat, somewhere in Australia.
Boat: Swanson 42 & Kelly Peterson 44
Posts: 8,422
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Bending stainless steel tube for a bimini
Hi all,
I’m looking for ideas on bending stainless steel tube for my bimini. I will be working with 25 mm (1 inch) tube with, I think, 1.6 mm wall thickness.
It’s the stuff that gets used on most boats, the sort that comes with neat little clamps and end bits to make T joins.
I am blatantly copying a design from a friend’s boat which is plenty strong enough and looks pretty smart too.
I can weld stainless (slowly) but I’ve hit a road block when it comes to bending the stuff. It turns out the hand bender I was hoping to use has a greater radius than I’d like. It’s pretty close to 4D (4 x pipe diameter, ie. 100 mm) but I really need to get down to 2D.
Looking around online it seems that the benders capable of doing the tighter radii are all expensive electric devices.
If the worst comes to the worst I guess I can send the tubes off to be bent, or weld in elbows, but ideally I’d love to find a hand bender that can do the job. Or, learn some clever technique that I don’t know about.
I know it must be possible as I see plenty of 2D bends on biminis around me.
Can anyone point me to either a hand bender or a technique for getting these bends? I’m happy to fabricate something if needed.
Matt
__________________
Refitting… again.
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25-06-2022, 06:27
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#2
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Senior Cruiser

Join Date: Dec 2008
Location: Noank, Ct. USA
Boat: Cape Dory 31
Posts: 2,852
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Re: Bending stainless steel tube for a bimini
Perhaps it would be easiest to pay someone in the business to bend the tube to your specifications. You are not limited to sailmakers as businesses who fabricate awnings also possess the equipment. Many larger electrical contractors also bend conduit into intricate shapes and might be another non-marine source. The task is simple with an electric or hydraulic tube bender and they will have an array of mandrels. A sailmaker/marine canvass maker may be reluctant as they see you as competition whereas outside the marine industry you will be seen as a novelty and they may charge very little for the service.
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25-06-2022, 06:42
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#3
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Registered User
Join Date: Oct 2017
Location: Detroit
Boat: O'Day 30 CB
Posts: 169
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Re: Bending stainless steel tube for a bimini
40 year canvas pro here.
There is a mean, expensive, learning curve for bending tubing. You want to find someone who has done this before. For a one-off, you can easily scrap more tubing than it would cost to hire a pro. I'm not aware of any hand bender that can bend SS at 2D. Expensive power equipment will be needed.
Most areas have a shop or two that specializes in SS tubing fab. I bend 7/8" SS frames and farm out anything with bigger diameters.
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25-06-2022, 06:47
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#4
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Registered User
Join Date: Sep 2011
Location: Good question
Boat: Rafiki 37
Posts: 12,987
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Re: Bending stainless steel tube for a bimini
I designed and built my bimini, but I hired a local canvas worker to do the bends. Didn't make sense to me to try and buy the right tool for such a small need.
Took him minutes to do the job, and do it well. He got paid well, I was happy. Perfect.
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25-06-2022, 07:37
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#5
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Registered User
Join Date: Jun 2016
Location: Brisbane Australia
Boat: Schionning Waterline 1480
Posts: 1,854
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Re: Bending stainless steel tube for a bimini
I bought a cheap bender but as you point out it can only do larger bends and the roller does leave a light impression on the tube but it was neat enough that it looked intended and it was very easy to use with an extension bar for leverage and we got accurate, repeatable results - first time users.
We made 2x handrails and full width seating, cut, bent, welded, fabricated brackets and fitted in 2 days. Saved a bundle and it looks professional.
I think you might struggle to find someone to bend 50mm bends in 25x1.6 316SS. You might need to buy mandrill bends and weld them in. Our 100mm looks ok.
__________________
Regards
Dave
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25-06-2022, 09:48
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#6
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Registered User
Join Date: Jul 2015
Boat: Bruce Bingham Christina 49
Posts: 2,734
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Re: Bending stainless steel tube for a bimini
You need to use specific tubing mandrels (instead of pipe) to not get kinks in it. For 1" tubing would use a hydraulic bender. Also filling the tubing w/packed sand (and end caps) helps make smoother bends.
Successfully made some dorade guards many years ago when I had access to the correct mandrels. Tried it more recently had poor bends because I didn't have tight fitting mandrels. Out sourced it and they hit my specs perfectly.
Welding corners works has long as you can get everything back to the highly polished surface typically found in SS commercial tubing.
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25-06-2022, 10:43
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#7
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Registered User
Join Date: Aug 2006
Location: Skagit City, WA
Posts: 24,742
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Re: Bending stainless steel tube for a bimini
You are not going to do a 2" bend radius on 1" tube without an expensive bender that has a lubricated mandrel inside the tube. Even then a 2D bend is tough with out wrinkles.
Redesign your part to use the cheap conduit bender which is likely... what... 6D bend or more?
I've engineered manufacturing this stuff.
__________________
"I spent most of my money on Booze, Broads and Boats. The rest I wasted" - Elmore Leonard
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25-06-2022, 12:32
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#8
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Registered User
Join Date: Nov 2006
Location: Back in Northern California working on the Ranch
Boat: Pearson 365 Sloop Westsail 28 and 14ft.Whitehall pulling skiff.
Posts: 9,721
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Re: Bending stainless steel tube for a bimini
So this will make 7 replies in a row...farm the bends out. I know you are a DIY kinda guy. Just look at it as the money you have saved doing 95% of the work on your boat yourself. Spend a little on this one.
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"Life is not a journey to the grave with the intention of arriving safely in a pretty and well-preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming: Wow - what a ride!"
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25-06-2022, 12:57
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#9
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Registered User
Join Date: Oct 2013
Location: Lake City MN
Boat: C&C 27 Mk III
Posts: 2,083
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Re: Bending stainless steel tube for a bimini
Quote:
Originally Posted by Celestialsailor
So this will make 7 replies in a row...farm the bends out. I know you are a DIY kinda guy. Just look at it as the money you have saved doing 95% of the work on your boat yourself. Spend a little on this one.
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Sometimes it’s just “better “ to let someone else do it
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Special knowledge can be a terrible disadvantage if it leads you too far along a path that you cannot explain anymore.
Frank Herbert 'Dune'
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25-06-2022, 13:53
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#10
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Senior Cruiser

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 47,078
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Re: Bending stainless steel tube for a bimini
Quote:
Originally Posted by Cheechako
You are not going to do a 2" bend radius on 1" tube without an expensive bender that has a lubricated mandrel inside the tube. Even then a 2D bend is tough with out wrinkles.
Redesign your part to use the cheap conduit bender which is likely... what... 6D bend or more?
I've engineered manufacturing this stuff.
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Hand benders, for 1/2" [I.D.] EMT conduit have a minimum radius of 4" [8 x pipe I.D.].
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Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"
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25-06-2022, 14:01
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#11
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Registered User
Join Date: Sep 2008
Location: On the boat, somewhere in Australia.
Boat: Swanson 42 & Kelly Peterson 44
Posts: 8,422
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Re: Bending stainless steel tube for a bimini
Well, I’d call that a consensus. Seems I wasn’t missing anything, it’s going to need someone with the fancy machine or weld in the elbows.
Thanks all.
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Refitting… again.
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25-06-2022, 14:35
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#12
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Registered User
Join Date: May 2008
Location: puɐןsuǝǝnb 'ʎɐʞɔɐɯ
Boat: Nantucket Island 33
Posts: 4,856
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Re: Bending stainless steel tube for a bimini
If you fill tube with sand and cap prior to bending in a typical pipe bender, it will be less prone to kinking but still won't be able to do tight bends. If you can weld tube, you can buy mandrel bent bends. and fabricate your own sections.
If it's a bimini, you can buy cast bends and bolt the whole lot together. Costs more in parts, but is the easiest solution. Also plenty strong enough and if you aren't convinced, you can tack weld the bolted sections together after assembly for extra strength.
I've never done it, but I've seen "one off" mandrel benders made using plywood as a former. Still can't get tight bends though.
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25-06-2022, 14:56
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#13
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Registered User
Join Date: May 2011
Location: Miami
Boat: EDELCAT33
Posts: 657
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Re: Bending stainless steel tube for a bimini
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25-06-2022, 15:18
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#14
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Registered User
Join Date: Sep 2008
Location: On the boat, somewhere in Australia.
Boat: Swanson 42 & Kelly Peterson 44
Posts: 8,422
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Re: Bending stainless steel tube for a bimini
Quote:
Originally Posted by carlosproa
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My gawd, I wouldn’t trust that thing on a baby’s bassinet, let alone a blue water yacht.
And that looked like the bends were about 20D.
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25-06-2022, 15:22
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#15
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Registered User
Join Date: Sep 2008
Location: On the boat, somewhere in Australia.
Boat: Swanson 42 & Kelly Peterson 44
Posts: 8,422
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Re: Bending stainless steel tube for a bimini
Quote:
Originally Posted by Reefmagnet
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If it's a bimini, you can buy cast bends and bolt the whole lot together. Costs more in parts, but is the easiest solution. Also plenty strong enough and if you aren't convinced, you can tack weld the bolted sections together after assembly for extra strength.
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I was gifted a lot of the stainless in the form of a bimini from another boat and it came with heaps of those connectors. I’ve kept them in mind but the design I am copying doesn’t need them.
I think they may come in handy for other jobs tho. I like the idea of welding them, I’ll give that a go.
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