exhaust fabrication

[trikerdrew]

Any of you metal fab guys care to tell me how the hell to bend thin gauge tube?Someone said fill tube with sand but it didn't bend well at all.Got a pipe bender which I know is made for heavier stuff but need a one off zorst and want/need to build myself.
Any ideas,constructive/enlightening would be good! :)

[badvoc]

Any of you metal fab guys care to tell me how the hell to bend thin gauge tube?Someone said fill tube with sand but it didn't bend well at all.Got a pipe bender which I know is made for heavier stuff but need a one off zorst and want/need to build myself.
Any ideas,constructive/enlightening would be good! :)

most guys I know that make exhausts buy the bends somewhere (not sure where) as in the have little bits of pipes that are just a bend, then the weld them to straight bits etc to make a pipe rather than bending a pipe to be the right size. This may not be common practise but I know a few custom builders that do it that way over here.

[dracken1]

to bend exhaust pipe you need a lot of money to buy a mandrel type bender to do the job.
as stated above buy the bends and straights and go from there. get the joins a good fit so after welding you can lenish the welds down.
most exhaust centres have contacts for bends in varios degrees and diameters :)

[Blackjack]

Mandrel bent stuff looks best, compression bent stuff is OK if it's done by some one who knows how to use the bender! trying to bend 1.5mm wall tube on a hydraulic pushthrough type pipe bender isn't going to be easy if it's possible at all!

Merlin motorsport sell bends in mild steel merlin's website and catalogue (http://www.merlinmotorsport.co.uk/)

If your using one of those afore mentioned hydraulic pipe benders, then the tube needs to be a tight fit in the shoe. Since the shoes are sized for pipe and not tube, you've got a problem. Try getting a piece of ally and annealing it by heating with a propane torch until the wooden end of a match stick leaves a BLACK (not brown, black) line when dragged across it.

The ally wants to be of a thickness that's half the difference between the OD of the tube and the width of the shoe.

Bend it into a "U" shape round the tube and stuff the whole thing in the shoe then bend it as far as you can. Pack the tube with DRY silver sand and plug the ends. Welding a plate on one and driving a wooden "carrot" in the other helps keep the sand packed nice and tight, but you may need to drill the tube and secure the carrot with a couple of screws.

First one will probably be pretty awful, but what you're trying to do is make the ally into a sleeve for the shoe, so you could quite happil;y use a piece of thick wall tube with the same OD as the exhaust stuff.....

What happens is that be cause the tube doesn't fit the shoe that's supplied with the bender, as it starts to bend the cross section deforms until it meets up with the shoe. By then its too late as the tubes going to kink now. The ally sleeve stop the "sides" of the tube from moving out and gives you a fighting chance of getting a bend in it rather than a kink. The sand packing can only do its job if its dry and fine as it needs to "flow" to adopt the new shape. Wet or coarse sand won't work, "Sharp" builders sand is no good for instance.

If you live near an abbatoir, you might be able to get horse's hoof glue. This will melt over a pot of boiling water, and pour into a warmed tube then reset. This was a traditional method of packing tubes for nice bends. Once its bent you can reheat the glue and pour it out of the tube, though when you fire it up for the first time that is probably going to stink! There's also some stuff called Serabend or Cerabend which is an alloy of lead tin and antimony (I think!) that melts a the boiling point of water which is used for the same thing. But it's expensive and if you over heat it its buggered, so melting it out with a blowlamp isn't reccomended, you really need to immerse the parts in water and boil them to ensure you don't kill the Serabend.

[devon-tony]

while on the subject of exhausts, Im currently making mine, got the bends all right, now have cut 2" out of the top part of the headers to get the whole system closer to the engine, and need to get the tops "rolled" need to get that top hat flange around the top for the collets and then the clamping plate to push on against the exhaust gasket, place that did the pipework cant do it, so what am I looking for machine wise to do it, then can ring around

thanks

Tony

[xjtriker666]

45-90 degree bends will cost ya bout 5 quids each....35-45mm.. then get some one to tig weld um for ya .......ny on impossible to bend 11/2mm wall stainy wiout havin mandrill bender....trust me i tried with clarke hydraulic bender.crushed them .........

[smeghead]

while on the subject of exhausts, Im currently making mine, got the bends all right, now have cut 2" out of the top part of the headers to get the whole system closer to the engine, and need to get the tops "rolled" need to get that top hat flange around the top for the collets and then the clamping plate to push on against the exhaust gasket, place that did the pipework cant do it, so what am I looking for machine wise to do it, then can ring around

thanks

Tony

the quickest and bestest way is to cut four pieces of tube from tube the next size up and weld these to the pipes the correct distance from the head, this will give you the flange required for the exhaust clamps to press against, if you havent got those the cut them from 1/4 plate , i would try and explain how to mark out the plate for the clamps but it went right over my head.(even the guy explaining laughed )

[trikerdrew]

Try sand as Blackjack suggests then poss s/s bends and weld up if that works out in m/steel.
Cheers :)

[guydewdney]

one way of making flanges for the ends of pipes is to use a 1/2" drive socket (for example) with a 40mm 'nut' size -

the socket is 'small' around the square, and 'big' around the 'nut'

the shoulder gives a nice curve - beat the crap out of it upsidedown in the end of the pipe (heat it first) and it 'rolls' the end round.

or just weld a washer on the end...


i use stainless steel pipe from a dairy manf place - 45 / 90 etc bends in lovely s/s. for slight bends the old slice, tig / slice / tig method works as well - but is very labour intensive.

[titusni]

most guys I know that make exhausts buy the bends somewhere (not sure where) as in the have little bits of pipes that are just a bend, then the weld them to straight bits etc to make a pipe rather than bending a pipe to be the right size. This may not be common practise but I know a few custom builders that do it that way over here.

Yeah, my trike guy's making me a new set of downpipes this weekend and he's using stock bends. He agreed that trying to bend stainless pipe was a pain in the arse.

Will be interesting to see the end result...

[Blackjack]

....<snip> trying to bend stainless pipe was a pain in the arse.

Will be interesting to see the end result...

Depends on the tube. 316L is a comedy job unless you've got a mandrel bender.

Other grades are more amenable, but it's going to depend on the quality of the bender you've got.

As for collet flanges, s'easy. All you need is a pair of mole grips. It's best if they actually say "Mole" or "Vise" grip on the side, but chinese copies will work as long as they aren't too shoddy. Just scribe a line round the end of the pipe, clamp the grips onto it so the end of the jaws line up with the scribed line, and bend it outwards. You're looking to make at least four trips around the tube to get a 90 degree bend, so don't go too far at a time. If you get a piece of the next size up (1/8" larger OD) and put a flange on that you can then saw off the appropiate length of it, and cut it in half lengthways to make the two collets.

The actual retaining flanges that go onto the head can be carved out of ally using holesaws. The big tip here is to use a big enough saw to make a groove for the collets to sit in, BEFORE you saw out the hole for the pipe itself.

So if you've got 1 1/2" pipes, you made the collets out of 1 5/8" tube and the flange on the collets can be filed or sanded to 1 3/4" OD before you cut it in half lengthways. In this case using a 1 3/4" hole saw to cut about 1/8" into the retaining flange blank, then using a 1 5/8" hole saw to do another 1/8" deep groove, followed by a 1 1/2" one to make the hole for the pipe to pass through will leave a 1/8" deep recess for the collet shoulders to sit in, though you may have to do a bit of a clean up with a small file or a dremel.

Next, how to build a steam powered timer for an automatic washing machine using old socks, a Fairy liquid bottle and some knicker elastic.*










* This article has been delayed indefinitely as the result of a rather nasty incident invovling a boiler explosion possibly related to the inability of a knicker elastic reinforced Fairy liquid bottle to retain 130 psi of steam pressure for periods greater than approx. 1.3 pico seconds......

[titusni]

Got my trike back and the new downpipes look the business - no sign that they're bends and straights welded together, the guy did a nice job :-)