Bending steel tube

[Mike Hibbins 1Participant @mikehibbins1]

[Mike Hibbins 1Participant @mikehibbins1]

I need to bend some 16mm X 1mm wall steel tube to make an
exhaust for a model aircraft.

I’ve looked at commercial benders but can’t find anything 16mm.

Has anyone got any ideas??

 

Edited By David Clark 1 on 22/02/2010 15:00:18

[Alan Worland 1Participant @alanworland1]

Hi Mike,

 

I have bent smaller steel tube by filling it with copper wires

from cable – it seemed to work quite well.

Used also to be done in the old days by filling with sand

 

Alan

Edited By David Clark 1 on 22/02/2010 15:00:38

[mgjParticipant @mgj]

I have one idea- use ali instead. Used to do a lot of tuned

pipe headers in ali – softer than steel, and with these

ali-weld kits, pretty easy to join. If you are going to use ali,

make sure its not heat treated to 1/2 hard. If you want to

 use steel, anneal. (Why steel – isn’t weight a problem?)

 
However the basic procedure is tolerably simple.

Make a “blank” in soft wire first as a gauge.

Plug one end with solder or epoxy. Fill with sand.

Plug the other end and bend over formers.

Ideally the former wants to have a groove at least 50% of the

pipe dia in it to stop wall collapse. 

 
Unwise, I’m told to use copper by the way.

Something in my mind says copper and ali pistons don’t

go too well, but maybe that is only in petrol engines.

 

Edited By David Clark 1 on 22/02/2010 15:05:46

[Gordon WParticipant @gordonw]

I use lead as a filler if at all pos., sand is messy, and if heat

is needed must be very dry.

Cheap plumbers benders with ally formers are made for std.

15mm o/d pipe and are easy to file out  to 16mm if required.

For one offs formers from wood are OK.

Copper exausts make a nice noise, and should be easy to

keep away from the piston.

 

Edited By David Clark 1 on 22/02/2010 15:06:31

[Peter GainParticipant @petergain89847]

Try using “Wood’s metal”. It has a very low temp melting

point of 100c.

Use as for lead, plug one end, fill with Wood’s & bend.

Easy to melt out.

Available from Alec Tiranti.

I have not checked to see how competitive they are price wise.

 

Edited By David Clark 1 on 22/02/2010 15:06:56

[mgjParticipant @mgj]

Copper – yes it does make a nice noise, but its not the copper

in contact with the ali – its the products of combustion, copper

and ali. Get a lot of pitting on the top of the piston crown etc,

as I recall, but quite willing to be corrected..
 
May not apply to engines running on methanol.
 
I agree – sand is messy, but a 16mm tube full of solid lead or

woods metal is going to take a bit of force bending?

All you have to do is drill a small hole in each plug to let the

steam out (if any). Best to dry your sand in the oven in a tray – or

one of those big sweet tins. ( Or a few holes in the end bits you

are going to saw off.) At least with sand you can just pour it in,

without worrying about molten lead, so one might define messy

as relative?

 
16mm, if you anneal or normalise it’ll bend cold with the right

former. Might be worth choosing the right grade of steel at that.

Cold Drawn Seamless is not going to help anything!

 

Edited By David Clark 1 on 22/02/2010 15:09:16

[D.C.ClarkParticipant @d-c-clark]

Fill the pipe with water.  Freeze it, bend it, thaw it. 

Lower melting temperature than lead or Cerro alloys, safer

 and easier to work with, much cheaper. 

This time of year, in most of the Northern Hemisphere, you

don’t even need a freezer.

 
David Clark in Southern Maryland, USA

 

Edited By David Clark 1 on 22/02/2010 15:08:56

[JasonBModerator @jasonb]

You can get 16mm conduit benders,

may even be able to hire one for a day.

Jason

 

Edited By David Clark 1 on 22/02/2010 15:14:14

[Tony MartyrParticipant @tonymartyr14488]

 

I spent a happy year of my apprenticeship bending steel

and nickel-copper-iron tube into complex shapes and fitting

them to Admiralty turbines. For steel tubes we always used

fine dry sand thus – wooden plug in the tube and pour in

sand, tapped the tube over its full length, pour in more sand

and repeat until the level drops no more then drive in top

wooden plug – heat the tube in the area of the bend and pull

into shape when bright red. Now the fun bit; cut off the ‘spare

end’ complete with plug and pour sand into dry container then

heat the other end just before the pug until red hot then turn off

oxygen and blow acetylene up the tube until it explodes and

blows the plug out as a smoking projectile far down the

pipe-shop – highly satisfying!
I feel obliged to say = ‘Don’t try this at home’

For exotic (seawater resistant) and thin walled pipes we always

used lead which was much hotter work and far less fun.

Tony

 

 

Edited By David Clark 1 on 22/02/2010 15:10:12

[MichaelRParticipant @michaelr]

You could maybe get a suitable sized bending spring to fit

the tube, and give that a try, used with a simple wood former

it may do the job.

Edited By David Clark 1 on 22/02/2010 15:10:47

[Ian S CParticipant @iansc]

Mike,what radius is the bend?

[Mike Hibbins 1Participant @mikehibbins1]

Thanks for all the advice.
 
To answer one or two questions:-
The weight of steel over aluminium is not a problem, with a

70cc twin turning a 23in prop a few grams won’t make any

difference.
I’m not totally sure of the radius yet, I haven’t finished the

design of the silencer. I guess somewhere around 80mm.
 
I’m going to start experimenting with some of the techniques

suggested, I’ll let you know how I get on. 

 

Edited By David Clark 1 on 22/02/2010 15:11:12

[CirclipParticipant @circlip]

At that radius, you can almst bend it over your knee.

Seriously, by using a grooved wooden former and a grooved

wiper roller you could probably bend it in a vise.
 
 Used a “Cheap” conduit bender to form a Stainless airline

system without kinks.
 
  Regards  Ian.

Edited By David Clark 1 on 22/02/2010 15:11:39

[Ian S CParticipant @iansc]

I used 16mm steel tube(its proberbly 1.5MM), when I built
a trailer for my bike,it had the the bends built in.I use an

old tubular folding chair,saved a lot of work,and looks good.

Ian S C

 

Edited By David Clark 1 on 22/02/2010 15:12:06

[EastleighiteParticipant @eastleighite]

Use a plumbers bender with a 22mm former.
Cut 6in. pieces of 22mm copper tube in half – ‘lengthwise’,
(enough to pack out the former and slide) . 
Anneal the steel tube. in way of bend,  insert 15mm. bending 
spring and away you go.

Edited By David Clark 1 on 22/02/2010 15:39:23

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