Exhaust tube bending

Discussion in 'Motorized Bicycle Welding, Fabrication and Paintin' started by wret, May 12, 2014.

  1. wret

    wret Member

    Joined:
    Feb 24, 2014
    Messages:
    333
    Likes Received:
    9
    I tried out an idea for bending exhaust tubing with a pipe bender. I filled the tube with hardwood dowel pieces with a 1/4" hole drilled through them. The wood support prevents crushing the pipe. I got a little over aggressive and got a couple of kinks but nothing that looks like it would restrict exhaust flow.

    The wooden dowel can be easily burned by injecting some compressed air and heating a section of pipe until the wood ignites. As soon as each piece looses a little diameter, they pop right out.

    [​IMG]
    [​IMG]
     

    Attached Files:

  2. mapbike

    mapbike Active Member

    Joined:
    Mar 14, 2010
    Messages:
    5,380
    Likes Received:
    1
    Looks like that worked out real good for ya, you can also leave a piece of pipe a couple inches longer than it needs to be, solder or braze a block off cap or plate on one end, fill the pipe with sand and then braze a cap. On the other end also, then you can bend the heck outta the pipe and it wont kink because the sand gets tighter inside as it bends and keeps so more pressure forcing outward in pipe that it holds it shape good.

    Just wanted to add another way to do it here also wret, hope you don't mind and it looks like you wound up with a real nice looking pipe there.

    Map
    .wee.
     
    #2 mapbike, May 12, 2014
    Last edited: May 12, 2014
  3. wret

    wret Member

    Joined:
    Feb 24, 2014
    Messages:
    333
    Likes Received:
    9
    I'll have to get around to trying the sand method one day!
     
  4. mapbike

    mapbike Active Member

    Joined:
    Mar 14, 2010
    Messages:
    5,380
    Likes Received:
    1
    here is a short video a looked up to show it being done with only using some good gorilla duct tape to seal off the ends after the sand is put into the pipe, cant get much easier than this...

    http://youtu.be/nM11rJ6K4Ys

    MAP
    dnut
     
  5. wret

    wret Member

    Joined:
    Feb 24, 2014
    Messages:
    333
    Likes Received:
    9
  6. 2door

    2door Moderator
    Staff Member

    Joined:
    Sep 15, 2008
    Messages:
    16,301
    Likes Received:
    25
  7. allen standley

    Joined:
    Oct 22, 2011
    Messages:
    775
    Likes Received:
    15
    shows time effort and determination useful beyond the motorized bicycle world. thanks!
     
  8. curtisfox

    curtisfox Well-Known Member

    Joined:
    Dec 29, 2008
    Messages:
    4,007
    Likes Received:
    31
    Wow! This is Koool love the homade tool to fourm the hose lip.........Curt
     
  9. wret

    wret Member

    Joined:
    Feb 24, 2014
    Messages:
    333
    Likes Received:
    9
    I played around with some 3/4 conduit tubing to make a cargo rack. Using the sand filing method I got some crimping on about a 1.5 inch radius bend but not too bad. I really think could have tamped better though.

    I tried the same bend with a dowel inside the tube and the tube crimped MUCH more severely. Sand filling is clearly superior.
     
  10. mapbike

    mapbike Active Member

    Joined:
    Mar 14, 2010
    Messages:
    5,380
    Likes Received:
    1
    I'm gonna try hard packed in wet sand in some tubing when I have a chance, in my thinking the wet sand will pack in better, which should take more pressure before the pipe tries to kink in the bend area..... I may be completely wrong to think this but wet sand become pretty dense when it packs so this is my thinking.

    Map
     
  11. wret

    wret Member

    Joined:
    Feb 24, 2014
    Messages:
    333
    Likes Received:
    9
    Wet sand "seems" like it will pack better due to the lubricating effect of the water. You actually don't want any lubrication when you do the bending. You want the grains of sand locked into an uncompressible matrix.

    Also, if you use water you would limit your options for applying heat to the bend area.
     
  12. mapbike

    mapbike Active Member

    Joined:
    Mar 14, 2010
    Messages:
    5,380
    Likes Received:
    1
    Lol.... water lubrication in the sand?

    I would never need to use heat with sand in the pipe, heating the pipe would defeat the purpose and actually weaken the pipe and cause it to wrinkle at the bend point, wet sand is very dense and the strength of it will be that it will pack so firmly inside the pipe that the more the pipe bends the more outward pressure the sand will apply, this is ehat I think will allow the bend to be done with less chance of the pipe crimping at the bend, once I give it a try I will know for sure, but wet sand will pack harder and denser than dry sand and almost act as though there is something more solid inside the pjpe as it bends.

    We shall see.....lol....!
     
  13. Davezilla

    Davezilla New Member

    Joined:
    Mar 15, 2014
    Messages:
    2,708
    Likes Received:
    1
    It looks like the sand method is good but it has to be tampped in there really good before attempting the bend. Wet sand might pack in better especially if you're using a much shorter section of tubing than that guy in the video, but worth experimenting with.
    I was going to get some Cerro Bend stuff a few years ago but didn't really have an excuse to buy it but I've seen that stuff in action and it leaves no kinks or wrinkles, and it's ultra low melting point makes it practical for home use or smaller scale projects like these bikes' exhaust systems.

    A while back I needed to replace some fuel line on one of my bikes and it takes a preformed hose with some really tight raduis bends in it, (dealer item only and Very expensive because of that) the regular hose would kink badly before going around the bends it needed to so I devised the idea to put a section of insulated 8 gauge solid copper wire inside the fuel line hose, then dip it in boiling water, take it out and bend to shape, let cool then remove the wire (wd40 helps a LOT here) and the hose held it's shape just perfectly.
    This works best with those clear or transparent colored fuel line hoses and you can get the bend radius as tight as needed without any worry of kinking or collapsing.

    I know this is off the real subject, but since we're talking about bending stuff without kinking it, it's worth sharing.... especially if someone has to route some 1/4" or 5/16" fuel line that needs a 1/2" radius bend and it keeps trying to kink shut. Hopefully someone can find this little tidbit helpful too...
     
  14. curtisfox

    curtisfox Well-Known Member

    Joined:
    Dec 29, 2008
    Messages:
    4,007
    Likes Received:
    31
    Awesome! Thanks that is good to know. I could of used that a while back. I ended up making a full circle loop to avoid the kink.........Curt
     
  15. wret

    wret Member

    Joined:
    Feb 24, 2014
    Messages:
    333
    Likes Received:
    9
    I had some scrap tubing pieces so I decided to perform a little experiment comparing the tube bending discussed here.

    Wooden dowel
    Sand
    Wet sand
    Sand / Heat
    Sand with welded bolts

    Here are the bends:

    [​IMG]
     

    Attached Files:

  16. Rump Rocket

    Rump Rocket New Member

    Joined:
    May 21, 2014
    Messages:
    26
    Likes Received:
    0
    Pipe benders are low cost on Flea-Bay, I guess it all depends on needs.
     
  17. mapbike

    mapbike Active Member

    Joined:
    Mar 14, 2010
    Messages:
    5,380
    Likes Received:
    1
    Looks like you had fun...

    Map
     
  18. CTripps

    CTripps Active Member

    Joined:
    Aug 22, 2011
    Messages:
    1,311
    Likes Received:
    0
    A neighbour of mine mentioned that salt is also a good 'tube filler' for bending. He prefers it over sand, as he knows he can get all the salt out of the pipe with hot water. Either way, looks like a good way to go about bending conduit.
     
  19. 2door

    2door Moderator
    Staff Member

    Joined:
    Sep 15, 2008
    Messages:
    16,301
    Likes Received:
    25
    Depending on how you 'cap' the ends of your pipe, but if it is capped sufficiently to keep the sand from squeezing out, I'd suggest you don't heat wet sand.

    Can you say, 'pipe bomb'? The steam that would be generated would make that a potentially dangerous thing to do. Even if it doesn't go 'boom' it might force the sand out under pressure. That could be nasty. Be careful, guys.

    Tom
     
  20. maniac57

    maniac57 Old, Fat, and still faster than you

    Joined:
    Oct 8, 2011
    Messages:
    4,486
    Likes Received:
    3
    Try filling a section with water and freezing it. Still needs capped ends but not sealed. Only one end needs to be sealed if you stand it up freezing it.
    Caps still play a part in holding pressure as you bend, but if you can hold the column from popping out the end it works.
     

Share This Page