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Old 11-01-2021, 14:16   #1
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Putting an arc in bimini tubing w/o a bender

If you wanted to put a 2 - 3 inch arc in an eight foot piece of 1" stainless tubing without the benefit of a tube roller or a pipe bender, how would you suggest doing it? It has to be repeatable, I need 4 sections.



A bonus is if you can come up with a way to do it while at anchor, and just using basic hand tools.


My idea so far is to take a piece of lumber cutting the arch into it and then use clamps to slowly pull the tube to the arc in the wood. Possibly use some heat to help it relax into the shape I want.


Any help would be appreciated.
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Old 11-01-2021, 14:42   #2
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Re: putting and arc in bimini tubing w/o a bender

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Originally Posted by sguerrero1971 View Post
If you wanted to put a 2 - 3 inch arc in an eight foot piece of 1" stainless tubing without the benefit of a tube roller or a pipe bender, how would you suggest doing it? It has to be repeatable, I need 4 sections.

A bonus is if you can come up with a way to do it while at anchor, and just using basic hand tools.

My idea so far is to take a piece of lumber cutting the arch into it and then use clamps to slowly pull the tube to the arc in the wood. Possibly use some heat to help it relax into the shape I want.

Any help would be appreciated.

I have a pipe bender and I wouldn't even try to bend (say) 25mm stainless tube. Any bend I want is done by either of two guys who make up ss fittings, guards rails etc for boats. But neither of them has roller equipment for putting gentle curves in ss tubing.

There are quite a few video clips, have you had a look at them?
https://www.google.com/search?client...urving+ss+tube
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Old 11-01-2021, 15:01   #3
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Re: putting and arc in bimini tubing w/o a bender

Save yourself a lot of grief.....find a canvas shop with a tube roller and pay them to do it for you. It doesn’t take them long.

All it takes is for you to ruin one tube and you have paid for the job...
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Old 11-01-2021, 15:23   #4
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Re: putting and arc in bimini tubing w/o a bender

Hi,

I do this for a living and the advice above should be heeded. It takes too much force to reach yield strength and create an arc, especially in SS, for the material to retain that shape. Heating chromed or SS will discolor it and damage the chemistry which will allow eventual oxidation. Saw you were in FLA? Try contacting Seco South in the Tampa area- if they can't roll it for you they could likely recommend someone. Mike Nelson would be a good person to ask there. I suppose if I absolutely HAD to do it myself, without a section roller, I would need a flat very stable surface that I could weld or otherwise strongly fasten a series of stops to lock in one end and fulcrum a point on the tube and very carefully use brute strength to pull it around into a curve, gradually moving the tube along against the fulcrum point, but it's an art, not a science and takes practice. With thin walled tube you need less leverage obviously but that material will be so much more prone to kink and then you're screwed. A shop shouldn't charge more than $150 to roll a single section of 8-10 LF tubing if they have the right dies. If you decide to try it against better judgement I'd suggest finding some spare material for experimentation. Best of luck.
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Old 11-01-2021, 15:32   #5
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Re: putting and arc in bimini tubing w/o a bender

2-3 inch radius on 1" tube? Nope. Not unless you have a fancy bender, maybe even one with an inside mandrel.

You can bend typical 1" stainless with a conduit bender, but it's far bigger bend radius, probably a foot or so.
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Old 11-01-2021, 15:53   #6
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Re: putting and arc in bimini tubing w/o a bender

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Originally Posted by Cheechako View Post
2-3 inch radius on 1" tube? Nope. Not unless you have a fancy bender, maybe even one with an inside mandrel.

You can bend typical 1" stainless with a conduit bender, but it's far bigger bend radius, probably a foot or so.
I read that as 2-3" of bend over the 8 foot length, say for the top of the bimini so it doesn't look flat.

Pete
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Old 11-01-2021, 15:54   #7
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Re: putting and arc in bimini tubing w/o a bender

I totally agree with all of the above.....I wanted to build my own bimini top.....but bending the tubing on my own quickly brought home the fact to let the pro's do it..
They can bend it "Exactly" how and where you want it...impossible to do on you own..

a bimini generally requires 4 pieces of tubing...so that is 8 bends...good luck trying this on you own....save yourself....a lot...and I mean a lot of grief....by going to a canvas shop..
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Old 11-01-2021, 15:59   #8
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Re: putting and arc in bimini tubing w/o a bender

yes, forgot to add....that the 8 bends....do not include the "2-3" bend (more of a curve really) in the overhead part of the tubing, you need that so that rain water does not collect.....so, that's actually 12 bends in all.....let the shop do it !!! they will bend each section so that it will " exactly" match the others....this is important come time to sew the fabric...I did my own fabric...looked ok....but you can tell it is "homebuilt"...
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Old 11-01-2021, 16:24   #9
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Re: putting and arc in bimini tubing w/o a bender

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I read that as 2-3" of bend over the 8 foot length, say for the top of the bimini so it doesn't look flat.

Pete
Ahh Ok I see. That needs support or it will give too much in one location. You have to stress it over the modulus of elasticity and not go too far. That's why a roller bender will do it well. You can make multi passes and creep up on it.

That's a challenge. So how tight a bend radius do you need which includes "springback" to end up there? You could end up with a number of attempts, Someone who does Bimini's could do it fast and it would be worth it.

the Radius of that arc 8 ft long and 3" high is about a 32 foot radius!

OP: have you considered finding a used Bimini for the tubing?? I bought one with good fabric for $200 off Craig's list. But if you want one for the tubing.... probably dirt cheap. I have one hoop here.
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Old 11-01-2021, 16:32   #10
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Re: putting and arc in bimini tubing w/o a bender

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OP: have you considered finding a used Bimini for the tubing?? I bought one with good fabric for $200 off Craig's list. But if you want one for the tubing.... probably dirt cheap. I have one hoop here.
Which is what I did, plus used a pulpit off another yacht to finish of the lower curved sections.

I think rather than bending I would laminate a GRP roof sitting on 4 poles like Matt and Jessica did (Funjohnson) on here.

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Old 11-01-2021, 16:46   #11
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Re: putting and arc in bimini tubing w/o a bender

While I would agree with the general opinion that you should get a shop to do it, it is possible to construct a mandrel bender of sorts out of plywood to do the shallow bends required.

A search of YouTube should return relevant results.
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Old 11-01-2021, 16:59   #12
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Re: putting and arc in bimini tubing w/o a bender

First off you are going down the right road with a 4 bow top. A three bow top is a much inferior arrangement. Over 50 years I have bent maybe half a dozen frames in aluminum and SS. Takes some pretty serious equipment with SS. As others have recommended find a pro shop and spend your effort on the canvas part. One other little trick is make the two internal bows about 1" narrower for a better look. Also a larger radius on the side bends looks better IMO.

Don't know about Marathon but bet money several shops in Miami.


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Old 11-01-2021, 16:59   #13
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Re: putting and arc in bimini tubing w/o a bender

From what I have read, the best way to prevent the bar from going flat is to seal one end, fill it with sand, then seal the other end, and then do your bend using heat.
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Old 11-01-2021, 17:05   #14
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Re: putting and arc in bimini tubing w/o a bender

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Originally Posted by Cheechako View Post
2-3 inch radius on 1" tube? Nope. Not unless you have a fancy bender, maybe even one with an inside mandrel.

You can bend typical 1" stainless with a conduit bender, but it's far bigger bend radius, probably a foot or so.

Agreed! I am about to have a steering guard/grab rail and the minimum radius they can do is 8 inch (which will be fine).

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Old 11-01-2021, 17:29   #15
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Re: putting and arc in bimini tubing w/o a bender

I too bend 1" SS tubing as part of my job. 7/8" is much friendlier and easier to work, but no where near as strong.

You can bend a gentle arc by marking carefully and just bending it in a fork of a stout tree- but- it's important that all the little bends are all in the same plane, and that this plane is the same as the leg bends. It's also important that each of the frames have the same bends- which is almost impossible without dedicated equipment.

It's expensive to have a shop do this work, but it's probably more expensive to attempt a DIY solution.
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