Source of alumin(i)um or maybe steel tubing

[offGridDownUnder]

My Greenspeed Magnum seat is welded aluminium tubing - two bent side rails connected with three cross rails. I need to duplicate it with some changes.

The tubing is 25mm OD and 2.5mm wall thickness - so 1" and 0.1" thick. The middle cross rail must be removed, so some change to stiffen the side rails is needed - larger OD, thicker wall, or double rails on each side welded together after bending into shape. The only purpose of that middle cross rail is to prevent the sides from bending inward. The seat cover is a mesh tube laced on with elastic cord, so very forgiving of modest changes to tubing size.

Heat treating isn't commonly available here outside of industrial batches, so I want material that doesn't require it, but can be welded. It's likely 6061 now, but that and 7075 are out due to the need to heat treat after fabrication.

I understand Al 5083 or 5052 will do, as will many steels. As it will be rained on, and painting the inside of the tubing isn't easy, I lean towards the Al, but happy to hear if you know a way to ensure steel won't corrode from the inside that I can afford for a one-off build.

I'd like a source to buy aluminium tubing to those specifications - can anyone tell me a reliable seller for small quantities of 5083 or 5052 tubing? 4 to 10 meters (as I may use some more for a framework to mount a roof on the trike).

Open to information about steel as well.

 

[Chalo]

7005 alloy is used for a lot of bicycle frames, because it solution heat treats at natural air cooling rates (when in bicycle frame sized cross-sections). So there are plenty of tubes available in bike-appropriate sizes. (Probably mostly in Taiwan and mainland China.)

You can get 7005 tubing from frame building suppliers in USA, but I have no knowledge of what's available domestically in Oz.

7005 Aluminum Plain Gauge

7005-T4 aluminum round plain- gauge tube sold by spec. Inquire with us for special requests or custom orders. Artificial age 7005 frames to T6 condition: age 6 hours at 200°F (+/-10°F) plus 4 hours at 320°F (+/-10°F). (Description: OD x Wall -Length)

bicycleframedepot.us

 

[Papa]

As it will be rained on, and painting the inside of the tubing isn't easy

To prevent Internal tube rusting, most frame builders use 'Frame Saver' after welding/brazing is completed.

Correct me if I'm in error, but, the end-joints of the middle (cross brace) tube on your seat frame is connected mid-ship of the side rail's bend. True? If so, you'll play hell duplicating the bend radius in 7005 (or nearly any aluminum).

My suggestion, for what it's worth... is to buy a more suitable seat frame and mount it. Maybe this one:

UTCustom Recumbent Aluminum Seat Frame

www.utahtrikes.com

 

[Papa]

Another option: Do you have a local source for some ½” EMT conduit? Assuming you have a MIG or O/A torch... fab a replacement seat frame:

Recycled Recumbents! - Seat frame construction

The first bend to make is for the 45 degree sweep at the very bottom of the seat. Set this in the bender’s clamp, mark on the bender’s start point, most of the pipe extended out over the tool. Bend to the guessed-at 45 degree point – remember that you have to bend a skosh past the mark to

sites.google.com

 

[amberwolf]

I'll second the Recycled Recumbent site; It's where I started out working on the original CrazyBike2's seat. I couldn't bend tubing so I first went with the padded-plywood version, soaked in water to soften it up for bending, screwing it to two planks I'd carved into the necessary shape as I bent it, every inch or so.

Later I welded up a seat frame for a suspended-mesh, using recycled steel tubing from a bedside potty chair. That one was used for the rest of the years of CB2's lifespan, and still exists, but nowadays (on SB Cruiser) I use a StadiumChair suspended-mesh seat since I'm not fully recumbent, just seated.