Tandem Tom

I have a chandiler project in which I need to bend the arms. They are 3/8" aluminum tubing. My idea is to fill with fine sand and bend around the forms. Wondering if applying hest would be beneficial?
Ideas would be great!
Thanks

unterhausen

some aluminums are more formable than others. You want to make sure the aluminum you have is capable of surviving bending.

There are many ways of bending something like that. You might be able to get away with a big enough radius bend without any filler. There is also freezing water or using a bending filler like cerrobend. I think there are resins that are similar.

fietsbob

My touring bike has loop stays of .049 wall x .75 OD 4130 made for building cargo bikes..

the builder buys them from a company with a powered mandrel bender, mandrel keeps the bent curve round in cross-section.

but has a floor mounted one with a long arm , for individual jobs ..



to bend thin wall tube a sand and pitch mix , maybe sand and wax would work , poured in hot then left to cool..
I used this in Art Projects with non ferrous tubes.. a malleable solid, sand alone will offer little resistance..


If the bend still ovals out, get a lot of steel ball bearings sized to fit down the inside of the tube,
and hammer on them until they fall out of the other end..

Maybe a Hydraulic Jack can apply force? the piece of course does have to be immobilized to not move from that force.

(adequate annealing heat and melting point threshold in aluminum is so close I would not try)







...

rm -rf

The right tool makes it easy.

Harbor Freight has inexpensive tubing benders. (Plumbers use these, too.)
1/4 to 3/8 inch

I got their 1/8 to 1/4 inch smaller bender to increase the bend in my V brake noodle from 90 degrees to about 110 degrees. It was very easy, and I could bend a little, test the fit, then bend slightly more -- very controllable.

This youtube video shows a fancier, precision bender in action: link.

These tools are designed to make a standard radius bend to different angles.

You can make larger radius bends by bending a little, then moving the tool up the tube and repeating. Maybe mark the tube with a sharpie for each movement distance.

You probably need a curve drawn on cardboard to match against each arm, to make it symmetrical. Test one to see if it scratches the tube finish at all, you might need something like scotch tape on the tubing. Maybe a few layers of masking tape on the tool's base hook.

Andrew R Stewart 

I spent some time at a local make it guy (jack of many trades). He has a few benders, he does mostly wrought iron stuff I think with them. One bender has pulley type forms and followers making me think it was for tubing. I suspect that there's a few fab shops in the Cleveland area with similar tooling. I'd call Dan at https://ciclipolito.wordpress.com/, he's got a lot of local contacts IIRC. Andy

fietsbob

tightly coiled steel wire , like an extension spring will slip over the thing that you want to bend..

if strong enough it will resist the Ovaling, where it wants to get wider
where you are compressing the inside and stretching the outside of the bend..

taras0000

I use spring coil benders at work all the time. Mostly for copper, but sometimes aluminum and steel as well. Adding heat can end up annealing the tube, which you may not want. Very soapy water, frozen, works very well, better than hot sand. 10-20% dish soap will do it. The problem is capping/sealing the tube, and having a freezer large enough to accommodate said tubes.

If you have non standard radii (as to most available tube benders) for your project, then you can source some pulleys with the appropriate groove diameter. You only need a small pulley as your follower wheel. You can use flat steel stock and drill out the appropriate centers for different diameter wheels. This can be easily mounted off the end of a bench/table.

Tandem Tom

Thanks for the replies!
After reading you're ideas and watching and reading some online sources I think I am ready to start.
I think I will go with sand and a limited amount of heat. I do have one of those tubing benders that I used for brake lines. That may come in handy for some tweaking.
Will report back!

fietsbob

I did say sand alone wont suppord keeping it round, it shifts easily, that is where the mix of pitch or wax wont shift,

canning wax is cheap and easily found, candle wax , etc..

Now for sand, if you fabricate a compressing clamp like a cable with 2 bolt threads on the end

you might be able to make pressure in the filling medium with washers and nuts tightening against each other..

taras0000

True. I have used plain sand before, when making bends in PVC pipe, and here it works well. No pitch or wax needed because you can fill the tube to maximum capacity and then cap it off. What little space is left is not enough to cause the bend to collapse. I do know that the soap and water method is used to make trombones horns and other brass instruments.

fietsbob

the capping with washers brought together by the internal cable clamp was a way of not letting the sand filling spill out..


I learned the pitch-mix technique from art metal working professors at Uni.

useful in making a raised image working from the back , then turning it over to detail its image

aka Chasing and Repoussé


nice hing about brass is you work it cold and anneal, it to remove work hardening then go at it another time, then repeat..





you do have a fuel bill making that heat ...





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taras0000

Just looked up Chasing and Repousse. I knew of embossing and engraving, but didn't quite know of the extent of how some techniques were done. That was really cool. It reminds me of some of the old aluminum oil rigger's hard hats that I've seen, they definitely made use of both of these techniques as well as fine surface engraving.

The heat bill things is definitely true. There are times where we have to make custom elbows and bends in large copper tube (2-6"). Often times it is time sensitive and cost prohibitive to wait on a fitting that has to be ordered in, so we make our own. Sheets of plywood and a table saw are used to make the dies, and we cap, fill, braze, and heat the tubing before using a hydraulic press to make the bends.