Bolt together frame?

Discussion in 'Photos & Bicycle Builds' started by cmb271, Jan 9, 2016.

?

Is it a good idea in concept to secure a frame together with nuts and bolts compared to welding?

Poll closed Feb 27, 2016.
  1. No, It's not strucuturally sound.

    20.0%
  2. Yes, If done properly

    80.0%
  1. cmb271

    cmb271 Member

    I maybe trying to reinvent the wheel right now but when it comes to frames do the they have to be welded, I've always wanted a motorized bicycle that had a more of a cruiser look to it and while a beach cruiser comes close I wonder what if you where to drop the bottom bar where the engine mounts to lower so there's more clearance. I always want to improve something and it dawned on me that to build my perfect bike I would have to build the frame and while I can mentally build a frame in my head I realize that I don't want to purchase and learn how to weld just so I can build a single frame.

    If I was to build a frame using square tubing what's stopping me from instead of using welds to secure the tubing together instead using harden steel bolts with rubber cushioning with a lock washer and a double nut tightening scheme to secure square tubing together. I understand this runs the risk of snapping a bolt under the vibrations but hypothetically if you where to cushion the vibration of the engine would it be feasible to build an entire frame using bent square tubing and a series of speciality nuts and bolts? I want to build a custom frame but I doubt I have the time or financial backing to both learn and acquire the equipment needed to weld and while I know I can just go to a private welder I have a bigger plan in mind and I want to prove something to myself.
     

  2. JimL

    JimL New Member

    Look up monocoque motorcycle in a google search. Such things have been done, but hardware attachments must be rock solid..no rubber, perfect pin fit or rivet fit, and similar to aircraft construction methods.

    Any possible movement at a bolt or impact-set rivet point will result in failure. The best process is to drill each hole undersize and then precision ream to a shouldered bolt fit. If you have bolt threads touching inside of the holes in your steel or aluminum, the threads will begin cutting the frame material with engine vibration.

    Shouldered machine bolts, precision fit, are remarkably strong for this type of construction. I built my own "homemade" lift gate (600 lb capacity on a $49 Harbor Freight winch) for the back of my Toyota flatbead. The entire parallelogram hinging mechanisms have run on these hardened shouldered bolts for over six years.

    You can buy those shouldered bolts in very small sizes!

    P.S. Consider choosing bolt shoulder size that matches a commonly available "automotive engine valve guide reamer" size. That way you can get a reasonable cost hand reamer (or low speed drill operated) which will give you perfect fit holes. Use a few drops of Tap Magic as you work. Serious Industrial Hardware stores are your friend for these type of projects. Also, use tubing spacers inside your square tube to prevent crushing. I use bolt shoulder length sizes that allows the shoulder to finish slightly sub-surface through the bolt clamped material. The nut actually locks both the bolt AND the material by its flat washer against the end zone of the shoulder.
     
    Last edited: Jan 9, 2016
    Timbone likes this.
  3. Timbone

    Timbone Active Member

    CMB, we are thinking along the same lines. There's no reason to think that a bicycle or motorcycle frame MUST be welded.

    I have a particular idea in mind, and I have started work on some basic blueprints, for a workable frame that would require minimum welding. The biggest problems to solved, as I see it, are a very secure headtube union and, if made into a softtail, the application for swingarm tubing.

    Keep in mind that many motorcycles include the engine as a structural member. There are no limits to what can be done.
     
  4. butre

    butre Well-Known Member

    They don't weld together bridges.
     
  5. wheelbender6

    wheelbender6 Well-Known Member

    The bolt-together frames can be done. Use aircraft lock nuts (with the nylon in them).
    There is a guy that makes recumbent bikes using a 4x4 cedar post for the frame.
    Many ways to skin a cat.
     
  6. JimL

    JimL New Member

    Good point about the wooden frame. There are a lot of fun and interesting ideas on this forum.

    Here is a neat little car that worked very well with a plywood frame. I got to test drive one, back in the summer of '66, at the Ring.

    https://en.wikipedia.org/wiki/Marcos_GT
     
  7. sbest

    sbest Active Member

    I had a 1967 Honda Dream that was a pressed steel frame.

    [​IMG]
    [​IMG]

    Remarkably strong and twist resistant.
    Something similar could be done with aluminum and bolts or adhesive and rivets.
    This guy has it nailed:
    [​IMG]

    Even easier, go cardboard:
    https://en.wikipedia.org/wiki/Cardboard_bicycle
    [​IMG]

    Steve
     
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