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Thread: Talented engineering folks.... Thin all chromemolly

  1. #1
    Registered User fantapants's Avatar
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    Talented engineering folks.... Thin all chromemolly

    So this is far and away beyond my pay grade gentlemen.

    Im good at joining the metels with fire and electricity

    But I'm curious to pick he brains Of The smarter gentlemen here regarding some specorocwlly ideas I have with chromemolly tubing

    Im lookong to make some racing frames this gear and have curious ideas regarding aero shaped tubing. There is a supply ( although limited) of aero shaped chromemolly but as I found out it is darling expensive. The aus guys I found only stock 1.6 mm and want 300 a m.

    A can get a limited selection of bike specific shaped tubes from the states for 70 a length. But I wanted more variety in sizing and liked the idea of a aus supplier.

    This leads me to my possibly stupid question.

    How do the smart boys think thin wall chromemolly (0.9 and 1.2 mm) would cope with cold shaping into aero form through pressing and die shaping?

    Would be done in lengths of between 700 and 900 mm.

    I "know" it's been done before on some well documented frame builds in the 90s before carbon became the go to. But to my knowledge they were simply squashed in a vice to a oval.

    Anyways. Any one with input feel free to yell at me or tell me im a genious lol

    Sent from my HTC 2PS6200 using Tapatalk
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    http://www.performanceforums.com/for...#post842594902 - making little toys for the big boys

  2. #2
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    Have done it before years ago at uni with 0.9 wall 4130 using a set of rollers. Was half inch and three-quarter tubing that we used. Ended up with a stadium shape rather than an oval, and had to be careful that the tube didn't twist in the rollers and leave you with a bit of a corkscrew. Couldn't compress the tube too far either otherwise the sides started to go concave into a figure-8 profile.

    In short, go for it. Just try on a few shorter lengths first to test the compression limits.

  3. #3
    Registered User fantapants's Avatar
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    Ooh that's positive

    Thanks man

    Sent from my HTC 2PS6200 using Tapatalk
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    http://www.performanceforums.com/for...#post842594902 - making little toys for the big boys

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    Just re-read your post. I had assumed you wanted oval tubing, not streamlined. Should still be possible, just more cumbersome. Go Gear Racing and Performance Metals should stock the streamlined stuff, no idea on pricing though.

    As an aside, we found it was more cost effective to get tubing laser profiled in the States and sent to Aus rather than buying material in Aus and notching it by hand. Convenient if you have a CAD model of your frame(s), less so if you are working it out on the fly.

    Edit: Something like this http://vr3.ca
    Machined not laser cut, but it was a while ago and I don't remember. Can assist with CAD stuff if required to meet their requirements if you choose to go down that path. Less time shaping tube = more time welding.
    Last edited by ricardo; 07-01-18 at 06:34 AM.

  5. #5
    Registered User dave1600's Avatar
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    If you'e going to try doing it with rollers, perhaps packing the pipe with sand as per sand bending exhaust pipe may help prevent it from collapsing into a figure 8 shape or otherwise deforming where you don't want it to deform ?

    The ideal way would probably be to "draw" it over a mandrel. The mandrel would slowly transform from inside diameter of the tube to the inside shape of the finished shaped tube, maintaining the same circumference to prevent having to stretch the tube as well as shaping it. You would need to find some way of forcing the pipe over the mandrel. Perhaps using a bottle jack or porta power or similar ? Rig up some sort of arrangement so you can mount the jack in line / parallel with the tube and "push" it onto the mandrel ? I do this to make exhaust pipes for the old Datsun which have to change from the rectangular exhaust port shape to round. Its a little easier though as it transforms over an inch or two so you can use a press to force a small length of pipe over the mandrel, your difficulty will be doing it to longer lengths will mean a press won't work.

    Just thoughts, obviously need to be fleshed out a little......
    Last edited by dave1600; 07-01-18 at 06:37 AM.

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    It's cheap as chips from Aircraft Spruce in the US, not worth mucking around trying to get it right yourself. Given that it is being sold for aircraft use it should be reasonably well made and not likely to fail.
    I reckon it would be quite hard to form into a uniform shape without significant setup costs unless you have access to some serious metal working tools

  7. #7
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    Another vote for Aircraft Spruce. I use them all the time for cheap 4130 in thin section or sheet form. 4130 is actually kinda hard to find locally for me-4142 bar and 4140 tube are in every scrap bin, but 4130 is much more weldable and less prone to cracking in thin section-so it's naturally more difficult to find!

  8. #8
    Registered User fantapants's Avatar
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    Yeah have a chat with our lord and Savior bill and he pointed me in the direction of the spruce guys. Prices see good so I'll try getting some lengths off them

    Thanks for the advice lads

    Sent from my HTC 2PS6200 using Tapatalk
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    http://www.performanceforums.com/for...#post842594902 - making little toys for the big boys

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