Frame material questions

Discussion in 'Motorized Bicycle Welding, Fabrication and Paintin' started by jokesonu, Aug 24, 2011.

  1. jokesonu

    jokesonu New Member

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    Some of you build your own frames. I would like to chop and stretch existing frame parts. What do you guys like for tubing? Is mild carbon dom tubing ok or do I have to go with chromoly? I can't find that locally. What wall thickness do you use? I am a good welder and would be using my tig, but I never tried this before. I want a longer wheelbase about 52 inches. Sure I could buy one but what fun would that be? Any advice or links would be appreciated.
     
  2. 42blue15

    42blue15 New Member

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    Mild steel is okay, not quite as stiff as cro-mo.
    Also, the DOM I have seen is not the same wall thicknesses (not as thin-wall) as the cro-mo usually is.

    For just one frame, it wouldn't be much to mail-order the tubing from somewhere online. You'd only need 3 or 4 pieces a couple feet long, at the most... That way you could first cut a donor frame up, and then order the cro-mo tubing that most-closely matches the frame's own tubes.
     
  3. culvercityclassic

    culvercityclassic Well-Known Member

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    I would get mild steel .065. That's what I have used to make a complete frame for my race bike. It does not cost much so you could get 20 ft for under 20 bucks. Practice before you start.
     
  4. jokesonu

    jokesonu New Member

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    Thanks Culver. .065 wow that's thin but I never been accused of underbuilding anything. We don't have real bike shops here in hooterville but I found a scrap pile of old bikes and frames in a pile ten feet high and thirty feet across. I pulled an old ten speed frame no wheels just a three piece crank with alloy chain rings and noticed it was tig welded so I gave it the ping test and I think its chrome moly it pings like a bell.

    I guess I have the start of a rat rod. The back half anyway. I'll practice welding mild to the rest of it and use 70 s2 filler and beat it with a bfh see how it holds up.
     
  5. 2nu2noBetter

    2nu2noBetter New Member

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    new here, but not to cycling in general. If you get CroMo tubing, do yourself a favour and do not buy butted tubing, as it is thinner in the middle than the ends. Single gauge CroMo is just easier to deal (as in weld) with. Low temperature fillet brazing does not weaken the materials as much as MIG or TIG. Maybe tack the pieces together and then braze?

    Hi-Ten steel is only about 15% heavier than Cro-Mo for a given strength, so if very expensive, just get what you can get, or hack up a salvage frame to get tubing and modify the frame you want to.
     
  6. retromike3

    retromike3 New Member

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    The main problem I see is not the material as the way you have to set the frame up or "tack" or "pin" it so that you get the correct angles and spacing. The book I got a few years ago was "the Pateriek Manual for frame builders". It show the complete steps from a to z on building a bike frame.

    As for My motor bicycle I started with a old Giant mountain bike frame and swapped the rear dropouts and changed the fork length ect, to get to the point were I was happy with the handling and placement of the wheels ect. I started by going to the local used bike place in Portland OR. The place is called "City Bikes" and for about forty bucks I had a strait frame to start with. The least amount you can pick up a set of frame tubes from a place like NOVA is about a hundred and fifty bucks and then your still not really set up to build a frame.

    The first bicycle frame I put together I did not do a very good job, but if you have the skills of a good welder than the most thing you have to deal with is the design of the frame. Its not super easy job to set up. I have a little program on my Iphone called "Size My Bike" and I am hoping it will get me a starting point for my next frame I will be putting together.

    there it a show on the Discovery Channel called "Cafe Racer TV" and they always start with a old motor cycle frame and then modify it to make it work for their needs. I have yet on that show to see them start fresh with just a set of tubes.

    For me I like steel because its very reliable I can guess when its going to get in trouble and can modify my design to suite.

    I like the stout CRMO tubing that my bike is made out of and on these kind of bikes I like to overbuild just for safety sake.

    the first frame I put together I made my own jig out of square one inch tubing and it did OK because all I did was to hold the steer the seat tube and the rear dropouts in alinement but my new jig holds all of the tubes right were they need to be.

    the first frame I put together was a set of TANGE Number three strait gage tubing with Columbus lugs and it took me about a week to get it right and even then I was not totally happy with the way it came out. Well its been about five or ten frames since then(including repairs) and I feel a little more confident now.

    as for material I say go with steel its been working for over a hundred years and it seems to do the job for me.


    mike
     
  7. jokesonu

    jokesonu New Member

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    Thanks for the advice retromike. I can see where the fixturing is the hard part. I wouldn't start with all new tubes anyway. I'll play with some junk frames and see what I come with. No hurry on my part. I want to start with a straight mountain bike type frame which I haven't even found yet. I'd sure like to see a picture of your fixture you made though.
     
  8. DaveC

    DaveC Member

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    I have what is basically a table frame I built. I've used it for many things. Made of 1x1 square tubing 5 feet long 4 feet high and 18" wide with frameing for another shelf 3 feet below the top. Just an open frame for welding things up. I'm thinking of useing this as a frame jig when I go to cut my frame up. I can tack weld rods from the holder frame to the bike frame to keep things in alignment. All the cutting and extending is in the front of the bike so the back half will be braced with 6 rods to keep things from moving around during welding, just have to grind the welds when I'm finished..weld

    Plan is to build this over the winter and have it ready for the car show this spring :)
     

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