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Old 25-06-2022, 01:01   #1
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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
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Old 25-06-2022, 06:27   #2
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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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Old 25-06-2022, 06:42   #3
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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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Old 25-06-2022, 06:47   #4
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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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Old 25-06-2022, 07:37   #5
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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.
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Old 25-06-2022, 09:48   #6
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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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Old 25-06-2022, 10:43   #7
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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.
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Old 25-06-2022, 12:32   #8
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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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Old 25-06-2022, 12:57   #9
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Re: Bending stainless steel tube for a bimini

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Originally Posted by Celestialsailor View Post
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.


Sometimes it’s just “better “ to let someone else do it
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Old 25-06-2022, 13:53   #10
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Re: Bending stainless steel tube for a bimini

Quote:
Originally Posted by Cheechako View Post
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.
Hand benders, for 1/2" [I.D.] EMT conduit have a minimum radius of 4" [8 x pipe I.D.].
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Old 25-06-2022, 14:01   #11
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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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Old 25-06-2022, 14:35   #12
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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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Old 25-06-2022, 14:56   #13
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Re: Bending stainless steel tube for a bimini

https://www.google.com/search?q=home...nfx-LQ18s,st:0

https://youtu.be/K3C0kOZu-VM
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Old 25-06-2022, 15:18   #14
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Re: Bending stainless steel tube for a bimini



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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Old 25-06-2022, 15:22   #15
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Re: Bending stainless steel tube for a bimini

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Originally Posted by Reefmagnet View Post

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 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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