Aluminium Sch 40 6061 tube bending for bimini frame

[chowdan]

Hey all,

As winter sets in and my drive to expand our living space a bit more and get us a bit more comfort outdoors during this time in the PNW, i think i'm ready to build out a bimini and enclosure to go with it.

Looking at using 1" sch 40 6061 T6 aluminum for the framing structure as this seems to be the cheapest. I need to double check my measurements with a bit more accuracy but i considered sailrites frame kit but i didn't like the idea of having seems/joints in the tubes.

I'm curious if anyone has used sch 40 tubing to build a bimini frame? How has it bent? I'd need to put a pretty sharp bend on the corners. I'm thinking maybe 30 degrees on the corners and then bowing the span length to get those legs closer the 90 degree turn?

I was thinking if i filled the entire length of tube with sand, throw a blow torch on it to heat it up a bit then toss it in a bender or maybe around a telephone pole or something large enough to give me the bend i need?

Anyone have opinions or thoughts?

[pdx_sailing]

6061-T6 is prone to cracking, 5086 will be easier to form. It doesn't have the strength as 6061 but after you torch it all bets are off. Have you called a local tube fabricator to see if they have the mandrels for sch40 6061-t6? It might be cheaper than you think to get the tube formed for a simple 3 bend U shape.

[chowdan]

Originally Posted by pdx_sailing

6061-T6 is prone to cracking, 5086 will be easier to form. It doesn't have the strength as 6061 but after you torch it all bets are off. Have you called a local tube fabricator to see if they have the mandrels for sch40 6061-t6? It might be cheaper than you think to get the tube formed for a simple 3 bend U shape.

Hrm i didn't think about the heat affecting the strength. I was thinking that the sand would help prevent the cracking issue though.

I haven't called around, maybe i'll pull some names this weekend and start calling to see what it'd cost to have them bend it.

As for 5086 - seems like online metals doesn't supply that in any sort of tubing, its all plate so thats out unless i can find someone locally to supply it. 6060, 6061 & 6063 in tube form and 6061 & 6063 in tube form :\ Wonder if Alaksa copper and brass in seattle can source 5086

[chowdan]

Looks like Alaska Copper & Brass can source 5086 tubing/piping.

Not sure if i need the extra wall thickness that sch 40 tubes provide - roughly 0.008" thicker.

[pdx_sailing]

yes alaskan copper and brass does have it, better prices too. Coast aluminum should be another option as well.

+.008 thickness shouldn't make a difference to the safety factor and if it does its undersized to start with.

metal scrap yards might have it as well for the best price.

[Baby tug]

You can buy 90° 45° fittings they might have a different name for them, I don’t know I guess , Weld them instead of trying bend the pipe, I know that’s what most of the fabricators I know do , Aluminum doesn’t like to bend in tight radiuses at least that’s my experience with it , I Built an aluminum hardtop for my cock pit on my Nordic tug 26 last year , i used fittings , Also aluminum can be a little tricky to Weld hiring somebody for $85 an hour is not that bad they can get a lot done in a couple hours ,
I could recommend somebody in my area to do it for you, also Alaska copper and brass is my go to place

[chowdan]

I was thinking about that. I guess I could do 45s/90s on the corner and put some bows in them.

I hadn't thought of that.

I don't think 5083 is an option from Alaska is way to expensive. They want $1100 for a 20ft tube lol Ill have to reach out to some scrap yards around and a few other suppliers around.

[RaymondR]

I have an aluminium bimini which uses some SS struts on the aft end. Like you I did not trust the fittings which are held together with a grub screw so drilled through both sides and used 1/4" SS rod peened over on the ends to better secure the fittings onto the tube.

[Panope]

Greetings Chowdan,

I could not find references to 1" schedule 40 Aluminum TUBE anywhere on-line including Alaskan Copper and Brass. I think you might be meaning to say that you want to use PIPE. Please clarify as 1" PIPE is significantly larger than 1" TUBE.

Here is 1" sch 80 6061 Aluminum PIPE with a bend radius of 12 inches that was bent COLD over a simple curved object. Pipe was NOT annealed. No pipe bender was used.



This is 1" sch 80 6061 Aluminum PIPE with a bend radius of 6 inches that was bent COLD after annealing. Bend was created by hand, over my knee without pain. This gives a very clear example of how much weaker the metal becomes after the heat treatment is removed.



The curved part of this component is 1" sch 40 6061 Aluminum PIPE with a bend radius of 12" inches that was bent COLD, without annealing, over a simple curved object. No tubing bender was used.


None of these bends shows any sign of "flattening" or "kinking" even though proper pipe benders, mandrels, or sand where NOT used.

My gut feeling during the bending process was that I was CLOSE to the minimum possible bend radius (12 inches for un-annealed, 6 inches for annealed). I never bothered to "take it past the limit" as I did not want to waste material.

The annealing process that I used was as follows:

1- Cover the area to be bent with soot from an acetylene torch with rich mixture.

2- Burn the soot away with acetylene torch with correct (no soot) mixture.

3- Be careful to not heat ANY more than necessary to remove the soot or the aluminum will turn to liquid.

Steve

[Madehn]

you might try a tubing bender that is used for electrical conduit- i used one from Home Depot to make all the bends i needed in SS tubing-- worked out fine and was not that hard to use-- had about a 3 foot handle and an arch on the bottom that held the pipe-- looked kind of like an oversized Ax only with an arched bottom instead of a straight blade. was not real expensive and worked well.-- incidently i would tend to use SS instead of aluminum- slightly heavier but much stronger- many fittings available to put on it and will never corrode. best of luck with project

[chowdan]

Originally Posted by Panope

Greetings Chowdan,

I could not find references to 1" schedule 40 Aluminum TUBE anywhere on-line including Alaskan Copper and Brass. I think you might be meaning to say that you want to use PIPE. Please clarify as 1" PIPE is significantly larger than 1" TUBE.

Here is 1" sch 80 6061 Aluminum PIPE with a bend radius of 12 inches that was bent COLD over a simple curved object. Pipe was NOT annealed. No pipe bender was used.



This is 1" sch 80 6061 Aluminum PIPE with a bend radius of 6 inches that was bent COLD after annealing. Bend was created by hand, over my knee without pain. This gives a very clear example of how much weaker the metal becomes after the heat treatment is removed.



The curved part of this component is 1" sch 40 6061 Aluminum PIPE with a bend radius of 12" inches that was bent COLD, without annealing, over a simple curved object. No tubing bender was used.


None of these bends shows any sign of "flattening" or "kinking" even though proper pipe benders, mandrels, or sand where NOT used.

My gut feeling during the bending process was that I was CLOSE to the minimum possible bend radius (12 inches for un-annealed, 6 inches for annealed). I never bothered to "take it past the limit" as I did not want to waste material.

The annealing process that I used was as follows:

1- Cover the area to be bent with soot from an acetylene torch with rich mixture.

2- Burn the soot away with acetylene torch with correct (no soot) mixture.

3- Be careful to not heat ANY more than necessary to remove the soot or the aluminum will turn to liquid.

Steve

Thank you so much Steve for commenting with some photos! You are right, i was looking at PIPE not tube.

Looking at outer diameter I think i will go with 3/4" 6061 sch 80 PIPE as it should only need a bit of grinding to fit any sort of off the shelf fittings that I need - if i dont go down the route of just custom making fittings.

I think 3/4 sch 80 pipe should be more than sufficient for strength and the cost of it is pretty reasonable.

It's good to know that you were able to bend the 1" pipe. It gives me a bit more confidence that I should be able to get the bends I am looking for without it having it kink on me. The span of the bimini will be roughly 110" +/- a few inches as I haven't taken proper measurements. Looking at your 12" radius bends, I am inclined to say that I should look towards that due to lack of a torch(though a friend of mine might still be around that has his, usually he packs up and heads south by now) and I might do a tighter bend. I wont be doing a flat "top" so I probably will only do about 30 degrees on both sides and put the remaining bend in the length of the tube to get the legs "straight".

I do appreciate you posting your images, it has helped me visualize a bit more what I'm trying to do. Your detailed explanations have been helpful as well!

[RaymondR]

When I purchased it my boat had an orthodox bimini on it with a small set of solar panels mounted on two arches over the top. The first problem I had with it was that there was no room for more panels.

In response I manufactured a horizontal support frame from aluminium, removed the panels from the frames and remounted them in the support structure and mounted the assembly on the arches.

This arrangement sufficed for a couple of years until I noticed that the cover needed replacing. Subsequent to a sever case of sticker shock I decided that the orthodox bimini was a poor design since it was not well fastened, restricted visibility, was to be expensive to maintain, restricted movement in the cockpit and did not allow rain catchment which would assist with keeping potable water in the tanks.

Consequently I decided to dispense with it, put a floor in the solar panel frame and mount it as a roof.

Whilst it no longer looks yachty, this has turned out to be one of the more practicable modifications I have made to the boat, In fact so practicable that I got rid of the yachty dodger (which had even more problems) and rebuilt it in aluminium and was able to install another 300 watts of solar into it.

It's your boat. Rebel against the orthodox. Go ferrel and rethink the project.

[chowdan]

Originally Posted by RaymondR

When I purchased it my boat had an orthodox bimini on it with a small set of solar panels mounted on two arches over the top. The first problem I had with it was that there was no room for more panels.

In response I manufactured a horizontal support frame from aluminium, removed the panels from the frames and remounted them in the support structure and mounted the assembly on the arches.

This arrangement sufficed for a couple of years until I noticed that the cover needed replacing. Subsequent to a sever case of sticker shock I decided that the orthodox bimini was a poor design since it was not well fastened, restricted visibility, was to be expensive to maintain, restricted movement in the cockpit and did not allow rain catchment which would assist with keeping potable water in the tanks.

Consequently I decided to dispense with it, put a floor in the solar panel frame and mount it as a roof.

Whilst it no longer looks yachty, this has turned out to be one of the more practicable modifications I have made to the boat, In fact so practicable that I got rid of the yachty dodger (which had even more problems) and rebuilt it in aluminium and was able to install another 300 watts of solar into it.

It's your boat. Rebel against the orthodox. Go ferrel and rethink the project.

Have any photos? Would love to see what you came up with.

I have been pondering different designs/ideas, but regardless i'll need to bend aluminum to build the structure as I'll want a curve to the top.

[RaymondR]

The dodger and the underside of the bimini.

[chowdan]

Originally Posted by RaymondR

The dodger and the underside of the bimini. Attachment 267131Attachment 267132

Thanks for those photos - Those look great. Functional for their purpose. I have been thinking about something similar, was thinking of using the FRP wall boards homedepot sells - 4x8 sheet runs about $40. I was thinking these could make up my "top" piece and i'd have curtains that i could sew up in Top Notch fabric(or sunbrella if i can find a deal). I dont expect anything fancy but being winter here in the PNW - and being a full time liveaboard while on the hook/mooring ball, it'd be nice to make use of our outdoor space a bit more without it constantly being soaking wet.

As it stands right now, I'm leaning towards having a full length pipe run up over and down at the forward end of our cockpit, with a brace coming out towards the aft of the boat, then another support that is coming out of our Atlantic Towers arch. Uncertain on the distance between the two but i may need to add an additional supporting brace to keep distances roughly 36" apart but that wont be until later.

The ideas just keep rambling through the brain as I am sick with COVID and my stackpack project has been put on hold until i get better. Hopefully this weekend I can continue to chip away at the stackpack otherwise it'll have to wait until Thanksgiving week. Once this is finished the next step is the bimini.