How do I hydroform a tuned pipe?

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builder bob

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I've got a 25cc weed eater engine on a model boat that i'm building and I want to make a tuned pipe for it. I have a program that will make templates for the different parts of a tuned pipe so you can custom make one but I like the look of hydro formed pipes better. I also think they'd be easier to put together. so I was wondering how I could use the roll up templates that the program produces to make two flat halves that when put together and expanded, would produce the right shape. the only way I can think of is to put the pipe together in paper and mush it flat so I could trace it on some metal. any suggestions?

oh and also what is a free program to convert DXF files to PDF?
 
builder bob

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nope but I thought a power washer would work. seen it done. or I could rent a hydrostatic testing pump.
 
Doc Sprocket

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Freaky! I'd like to see your process and result. If your printer is spitting out flat templates, what do you need to do with them?

Come to think of it, I think I was the Mythbusters do it once...
 
builder bob

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I can print templates for each cone and tube which I then could tape together and moosh, then trace on two pieces of metal, weld together and put 1000 psi of water into. so far I can only print mini pipes because I haven't figured out how to convert a DXF file to PDF
 
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mckutzy

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Isnt there a formula for this kinda thing.
I got a little too late here to answer.
Have you any experience doing something like this? Why not trying the weld together method first, then get a little technical.
then again...
Weren't you having a problem getting a welder or is this why you want the h2o formed one?
 
builder bob

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yup I still need a welder but I think that the exhaust temp is low enough to use alloys that can be melted with a torch. to hydroform the pipe you bend a 1/4" of the edge down along the sides of both halves, weld the halves together on the folds, weld a valve on one end and a connection for the hose on the other, leave the valve open until the air is purged, bring the pressure inside to around 800 psi and then use a torch and hamer to get rid of wrinkles, then go up to 1000 psi.
 
builder bob

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oh great I can't even water cool it down to 500F then! I realy need to learn to weld :(. do they get the exhaust temp up because more fuel is being burned at a time?
 
builder bob

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mckutzy said:
Isnt there a formula for this kinda thing.
I got a little too late here to answer.
Have you any experience doing something like this? Why not trying the weld together method first, then get a little technical.
then again...
Weren't you having a problem getting a welder or is this why you want the h2o formed one?
Click to expand...
I though I had answered what you wrote but either you edited what was there or I missed a lot of stuff.

I have never done any hydroforming but I also have never welded and hydroforming does not need as many welds. also the regular method of construction is hard to put bends in the pipe.

I do need a welder and need to learn to weld/
 
builder bob

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they may be good quality but the r/c engines they're designed for will be faster and have a different timing angle then an old weedy engine so I don't think they'd do much. they also cost as much as getting a good stock r/c boat engine so i'd buy the engine before I'd buy the pipe. i'd also like to be able to make tuned pipes because I fly nitro planes and so I could save a few hundred on pipes.
 
FatCat

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builder bob said:
they may be good quality but the r/c engines they're designed for will be faster and have a different timing angle then an old weedy engine so I don't think they'd do much. they also cost as much as getting a good stock r/c boat engine so i'd buy the engine before I'd buy the pipe. i'd also like to be able to make tuned pipes because I fly nitro planes and so I could save a few hundred on pipes.
Click to expand...

I forgot to post the link anyway. Lol. Can't blame you for wanting to build a pipe. It's a daunting task but could be very rewarding. If you can save a buck while your at it right on. I've got quite the collection of rc myself. Always liked the big planes but I havn't gone to the sky yet.
 
builder bob

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you definitely should fly. it's crazy fun; when you take off flying a difficult plane you'll start shaking until you land. then when you bring the plane in and go sit down you feel awesome!

can someone explain to me what length each cone of the tuned pipe should be by reading this quote? "You can manually plot the cones to build a paper model or to transfer the shape onto sheet metal by using the values of R and phi noted below each cone. Plot two concentric circles (having the same center) using the two radii R. The flattened cone spans a segment with an opening angle of phi degrees between the two circles."

also, don't expansion chambers work if they're curved? can they be curved in any spot as long as all the sizes are correct?
 
FatCat

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One day I will fly. Guy who owns the local hobby store tells me I need to start with a smaller hobbico? One. I want one of those giant ones he has hanging from the ceiling. He said they're hard to fly though. He said he'd come with me and run the trainer remote. I've slacked off the rc a lot. Life's been really busy for me lately.

On pipe design here's some good reading. I'll add more links as I have time.

http://www.dragonfly75.com/motorbike/ECtheory.html
 
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So bob, you now have some good theory reading, now after you brain is hurting from this, you will need tame that pain with some welding therory.
 
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