(MBBO#6 Class 2) Twist of Lemon

Discussion in 'MBBO 2017 BIKES' started by tjwilson, Sep 4, 2017.

  1. tjwilson

    tjwilson Pro Member

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    Frame Details

    frameWeldCleanup01.jpg

    frameWeldCleanup02.jpg

    frameWeldCleanup03.jpg

    Frame Pre-Seat Area Additions and Trim

    framePreSeatMods.jpg
     
  2. tjwilson

    tjwilson Pro Member

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    Seat Area

    My thought for now is to eventually add sheet metal to make the inner seat pan integral to the frame.

    Struts for added strength.

    seatStrutAdds.jpg

    Additional pieces to complete rear of seat.

    seatEndPieces.jpg

    Trimming, fitting and welding seat end.

    seatEnd01.jpg

    seatEnd02.jpg

    seatEnd03.jpg

    Seat Corners

    I capped the end of the rear horizontal tube with solid bar. This gave me enough material to go back and grind / shape the corners. Similar to how I rounded the front of the seat cantilever tubes.

    seatEnd04.jpg

    Seat Top Side Tubes

    seatEnd05.jpg
     
  3. tjwilson

    tjwilson Pro Member

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    Frame and Mock-up

    So I've made it to the point where I can finally test the strength of the frame's design. And... result is not quite what I had hoped for. The seat area seems more than strong enough. Problem looks to be flexing in the lower front part of the frame. This area basically forms a rectangle verses a typical triangle so is not as strong. The leverage created because of the top tube / seat connection point location relative to the lower frame is creating enough force to pull the head tube up and distort that rectangle. Not a terrible amount of movement but would make for a very squishy ride feel, not to mention the fatigue to the frame over time. Plan "B" is to add a second curved sweep piece to each side between the seat and cantilever tubes. That should reduce the leverage and hopefully tighten everything up (fingers crossed).

    While trimming and fitting the frame pieces I held up a second curved piece in that area (not trusting the design and in anticipation of having to make design modifications). Actually looked pretty good!

    Frame Overview

    That odd tube coming out of the bottom of the head tube probably needs a little explaining. I have the headset installed upside down so that I can insert a tube where the handle bar stem will eventually go. This slips into the fixture to hold the trail angle.

    frameOverview.jpg

    Mock-up

    The clearance between the rear tire and frame is real tight. The drop out slots will require some lengthening.

    mockup01.jpg

    mockup02.jpg
     
  4. Scribble

    Scribble

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    Well I already know who the winner is, this thing is gorgeous :eek:.
     
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  5. GuitarlCarl

    GuitarlCarl

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    I love the LOOK of the lower point in front of the BB, but will it be too close to the ground? I'm wondering about a subtle bend up in the lower tube in front of the BB (mirroring the subtle bend in the mid tube) and taking an inch or two out of the front curved down tube to the point... I can see cruising and turning sharp with the point dipping down and impaling the ground. There's gotta be close to 3" of clearance now, but is that enough?

    Carl.
     
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  6. Chad T

    Chad T

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    Really mind blowing...love the stance with the rake and tire stagger.
     
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  7. RustySprockets

    RustySprockets

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    Would small gussets help eliminate the undesirable flex?
     
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  8. GuitarlCarl

    GuitarlCarl

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    I have noticed frames often spring apart when cut. Makes me believe they are assembled under pressure. Similar to the roof trusses in your house, which are forced into place in a jig and then fastened together. Makes them stronger somehow. This could work on a bike frame too.

    Carl.
     
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  9. RustySprockets

    RustySprockets

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    Ooo...pre-stressed structures. What an innovative idea!
     
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  10. OneHorsePower

    OneHorsePower

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    Amazing ! :43::41:
     
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  11. tjwilson

    tjwilson Pro Member

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    Thanks. Clearance is just over that, somewhere between 3" to 3 1/2". Should be able to catapult pretty far if I time hitting the lower point and front disc brake just right! But yeah, could be an issue. Not sure how far the front will dip with the springer fork. I might have to limit the amount of travel. I can probably round the very front of the point and gain another half inch without changing the overall look too much if I need to. The cruiser I built for the WBO has about the same clearance. I have quite a few miles on that and haven't scraped the bottom tube... yet. Guess because I know I'm going to be the primary, or only, rider and that I'm aware of just how low it is, I'm willing to gamble that it won't be a problem. Definitely something I'll pay extra attention to on the initial test ride.
     
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  12. tjwilson

    tjwilson Pro Member

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    They probably would. Not sure that I could come up with gussets I'd be happy with though. If the curved side additions don't work that will be my next step.
     
  13. tjwilson

    tjwilson Pro Member

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    The Fork

    With nearly as many pieces as the entire frame, fabricating the fork was pretty time consuming.

    Tubing for fork polished, filled with sand, capped and put through the roller.

    forkTubing.jpg

    Fork Dropouts

    frontDropouts.jpg

    The Fixture

    The fork fixture with dropouts and pivot tubes held in location.

    fixture01.jpg

    Fitting and tack welding fork tubes.

    fixture02.jpg

    fixture03.jpg

    fixture04.jpg

    fixture05.jpg

    Dropout gusset template and cut pieces.

    fixture06.jpg

    Welded Forks

    forksWelded.jpg
     
  14. tjwilson

    tjwilson Pro Member

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    Mock-up with Fork

    mockupWithFork01.jpg

    mockupWithFork02.jpg

    mockupWithFork03.jpg

    While fitting the tubes that formed the fork I checked and adjusted the tubing positions against the frame. This helped make sure that the tubes would flow the way I wanted them to. In the process of these tweaks I failed to notice that the location of the front cross tube ended up low enough that it now interfered with the front tire! Luckily not by much. I should be able to dish out the bottom of the cross tube to create enough clearance.

    lowerBarInterference.jpg
     
  15. Chad T

    Chad T

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    Wow man wow!! Can't wait to see the rest of it...:43:
     
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  16. tjwilson

    tjwilson Pro Member

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    Fork Spring

    Didn't know exactly what I was going to do for the fork spring and mounting hardware. I orded a springer head kit thinking I may end up only using the spring. Looks like I'll be able to use most of it. I put the spring perch in a hydraulic pipe bender and bent it down to the angle I needed. The springer yoke comes up short even when flipped but I should be able to make something up that will work. Not sure if I've created a situation where there is now too much leverage, hopefully not. At a minimum I'll be using a grade eight replacement for the spring bolt.

    spring01.jpg

    spring02.jpg
     
  17. CRASH

    CRASH

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    This is rolling art. I love watching this come together! Gorgeous!
     
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  18. RustyGold

    RustyGold

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    ...exactly...what...he...said...:43::43:...x2 :grin:

    Jason
     
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  19. Dr. Tankenstein

    Dr. Tankenstein

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    First off, love the design of this bike.
    I see what you mean about leverage, the pivot action may force the spring down instead of back.... I guess if the front ‘legs’ of the fork were longer, it would bring the spring into a more parallel position and possibly enable use of the stock yoke?
    Since this is such a radical design, have you tried placing the spring perch under the bottom bearing race? At least then the fork legs would be moving in a downward direction and so would the spring...I’m no engineer, just play one....in my head.
    Really looking forward to the rest of this build.



    Sent from my iPhone using Tapatalk
     
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  20. The Renaissance Man

    The Renaissance Man __CERTIFIED DIVER__ (Open Water & Open Dumpster) Pro Member

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    Just now reading through this for the first time. When I saw @tjwilson listed next to the thread, I knew what to expect and you didn't disappoint! Subscribed!
     
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