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Old 22-06-2016, 11:36   #1
Guy
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Bending Bimini tubes

Does anyone know how to set up some rollers to curve/bend tubes for a bimini? I'm thinking some rollers bolted to the dock or some boards. I seem to remember something like that in front of a canvas shop once but I can't picture it anymore.
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Old 22-06-2016, 12:52   #2
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Re: Bending Bimini tubes

You can buy tubing benders that will likely work better than a jury rig. SS tubing can require quite a bit of leverage to bend.
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Old 22-06-2016, 13:50   #3
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Re: Bending Bimini tubes

Or just pay your local canvas shop to bend it for you. They already have the equipment and you arent likely to need to bend tubing on a regular basis.
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Old 22-06-2016, 14:13   #4
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Re: Bending Bimini tubes

If you insist on do-it-yourself bending... fill the tube with sand That will reduce the risk of "kinking" instead of making the smooth curve. (can't 100% prevent it without use of a proper pipe bender)

Common pipe bender an putting a cloth in to prevent scratches works...
But it takes a lot of figuring to know where you really should do the bend. It very easy to get a nice bend in the wrong place or at the wrong angle to a previous bend.

You can waste a lot of tubing learning...
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Old 22-06-2016, 14:19   #5
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Re: Bending Bimini tubes

A proper bender for thin walled tubing does not use rollers. It has a former one one side into which the tube fits that is the radius of the resultant curve and then it has a slide that follows the former on the opposite side. Rollers will not give a smooth curve and the tube will be wrinkled. Also, getting the correct distance between one curve and the next is almost impossible with rollers

So I second getting a professional to do the bends for you. Generally it is inexpensive and very accurate.

I know this because I tried. I eventually did all the pipework on my boat using professional bending and I have a lot of pipework (solid rails all round, full cockpit enclosure and a radar arch).
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Old 22-06-2016, 19:02   #6
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Bending Bimini tubes

I use a crowner and a Diacro bender... My canvas guy loves me because my frames match, are exact and symmetrical. I go with him to design frame and measure. I recommend finding someone who uses this method.

One local canvas shop has a simple plywood jig slightly smaller radius for spring back, a cleat to work against, crown by eyeball. They have years of experience.

Work from the center of the bow out, leave the legs a few inches long, cut with pipe cutter after test fit...lots easier to cut off!
Filling with sand does absolutely no good, it compresses and moves away from kink...a low temp melt material like bismuth, maybe on super thin wall stuff.


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Old 22-06-2016, 19:26   #7
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Re: Bending Bimini tubes

In a pinch, you make a former out of plywood screwed to another plywood board. Definitely use sand inside the tube. You won't get tight bends, though, unless you put some thought into the job. At the end of the day, bending with a mandrel bender is the way to go. Even car exhaust shops may be able to bend the stuff for you cheaply.
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Old 22-06-2016, 19:46   #8
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Re: Bending Bimini tubes

Just get an electrical conduit hand bender. Surprisingly , that's what some canvas shops use. Good bending machines are expensive. Beware that bending is a bit of an art. You will scrap some stuff. Start with lots of excess either side of the bend, you can then cut the excess off later. Write down exact dimensions of where you start etc, so you can duplicate the other side. Or you could spend $100k or so and do this: :>)
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Old 22-06-2016, 21:19   #9
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Re: Bending Bimini tubes

The sand works if the tube is FULL and you cap the ends. It has to be hard for the sand to get out.

Then when the bending is done you cut off the capped ends (because you allowed at least a few inches excess each end)

For bending small tubing to tight radii, I fill with salt so I can dissolve it out. Below 1/4 inch inner diameter the sand can get stuck in tight bends.
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Old 23-06-2016, 21:35   #10
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Re: Bending Bimini tubes

Hi:

After a failure another way, what I ended up with was a red oak disk about 12 inches in diameter to provide about a 6 inch radius. I glued up a blank, sawed it to a hexagonal shape, turned it round on my wood lathe. TThen I rough cut a groove with a gouge, followed by using a custom ground tool to finish turn a groove on the circumference to match my 7/8" 1/16" wall 304 SS tubing. I bolted this to my workbench. I screwed down a straight piece of wood 2 or 3 feet long to lead up to the disk to hold the trapped end.

I then loaded a piece of material and tried it ... just moved the workbench. Then I braced the workbench diagonally from a wall at the floor up to the top edge of the bench in line with the disk. Now I got somewhere. I managed a reasonable looking bend with a surprising amount of force needed.

Start with a piece that you figure is about 3 inches long, just to be sure. You need to carefully mark your starting position and observe what you get after performing the initial bend. The initial bend resulted in my piece growing about 1.5 inches in width, that is if I marked out for a 72 inch wide arch, I would actually get a finished width of about 75 inches. So knowing this after my first bend, I spaced my second mark at 69 inches to get a 72 inch finished arch width.

I have bent two arches for a bimini, and four arches (two bent at about a 45 degree angle) for a solar panel arch for my Tanzer 22. Each "45 degree" arches is welded below the 90 degree arch to form a truss like structure with some 3x3" 1/8" plate forming the webbing. I am happy with the bends, less so with the shaping and fitting of some of the pieces on the solar panel arch that were welded in place. It will work fine, but the joints are ugly.

If anyone requests, I can post photographs of the bending setup and the bimini frame and solar panel arch.

Boulter
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Old 24-06-2016, 10:15   #11
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Re: Bending Bimini tubes

Usually you can modify your plan to the bend radius available. Most railmakers don't use a mandrel inside the tube for bending. You can see this by looking at typical frames on other boats, slight distortion at the bend. You can also rent these as well as buy:
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Old 26-06-2016, 22:07   #12
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Re: Bending Bimini tubes

Quote:
Originally Posted by Guy View Post
Does anyone know how to set up some rollers to curve/bend tubes for a bimini? I'm thinking some rollers bolted to the dock or some boards. I seem to remember something like that in front of a canvas shop once but I can't picture it anymore.

Hi everyone,
I had a similar question when I was renovating my boat and needed to build a new bowrail out of 1" S/S tubing. I did some research on the subject and solved the problem without too many dramas. I made my own diy tube bender and in the end I had myself a brand new bowrail which I was very pleased with.

I thought I'd share my bowrail building technique on this thread too show it can be done. I have several photos of the process to upload and will post them with explanations a bit later on in the day. A bit short of time right now so, be patient, and stay tuned.

Back soon,
bony
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Old 27-06-2016, 00:38   #13
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Re: Bending Bimini tubes

Guy,

Here's a link to a new thread titled "DIY Bowrail" which I just started on CF It shows pics of my home made tubing bender. You might be able to apply the info to your bimini question.

DIY bowrail - Cruisers & Sailing Forums

bony.
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