(MBBO#6 Class 2) Twist of Lemon

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

  1. Chad T

    Chad T

    Joined:
    Sep 7, 2014
    Messages:
    2,751
    Location:
    Columbus OH
    Ah yeah I see that now...:39:...needs to be more square with the arc of that pivot point...what about lowering the mounting point of the spring so the spring is in a nice line with the top tube?..:cool2:...+ maybe a longer spring?
     
    Last edited: Oct 18, 2017
    tjwilson likes this.
  2. Dr. Tankenstein

    Dr. Tankenstein

    Joined:
    May 20, 2009
    Messages:
    5,618
    Location:
    Marietta, GA
    Maybe bend the perch to 90 degrees and point it down? I’m sure with your design skills, you’ll figure out a much more elegant solution than I could.....


    Sent from my iPhone using Tapatalk
     
    tjwilson likes this.
  3. tjwilson

    tjwilson Pro Member

    Joined:
    Jan 15, 2016
    Messages:
    359
    Thanks!

    Yeah, exactly... I hadn't really looked at how the original springer actually worked before designing the forks. Seems to be a recurring theme, making design decisions solely based on aesthetics! I had assumed it worked like a shock and the spring action was guided by the bolt. Taking a closer look the yoke/crown dosen't even touch the bolt in the original intended application. The hole the bolt runs through is 1/4" larger in diameter than the bolt. And, the fork pivot point is behind the spring front and pulls back on it. I've placed the fork pivot point in front of the spring and now I'm trying to push it.

    Hmmmm.... Sounds like an interesting possibility that I hadn't considered.
     
  4. tjwilson

    tjwilson Pro Member

    Joined:
    Jan 15, 2016
    Messages:
    359
    Thank you very much! I'm really happy with they way things are going so far and having a lot of fun with it.
     
    The Renaissance Man likes this.
  5. tjwilson

    tjwilson Pro Member

    Joined:
    Jan 15, 2016
    Messages:
    359
    Lowering the mounting point and maybe swapping the spring out for a longer spring, or mountain bike shock, might be the solution.
     
    Chad T and Dr. Tankenstein like this.
  6. tjwilson

    tjwilson Pro Member

    Joined:
    Jan 15, 2016
    Messages:
    359
    That would be really interesting combined with your suggestion of mounting the spring below the bottom bearings. Imagine a tie rod from the forks running to a lever that has a pivot point below the bottom bearings. The lever action then pulls down on a spring that runs parallel to the head tube. Maybe a little too Rube Goldberg for this bike, but I can definitely imagine an entire bike designed around that idea!
     
  7. tjwilson

    tjwilson Pro Member

    Joined:
    Jan 15, 2016
    Messages:
    359
    Spent a couple hours making up a rough crown/yoke to test if the fork spring would work and try to determine what direction I may need to go in with a potential re-design. Surprise, it worked as originally intended! I wasn't able to see any movement lateral to the direction of compression and the spring bolt cleared the holes without interference. Now I just need to make something that looks a little less "utilitarian".

    I included a small section of tube that the spring slips over in the design but it didn't behave like that was even necessary. I got curious enough to do a little searching online because it seemed so counter intuitive that this wouldn't try to buckle when compressed. Turns out the answer is in plain sight. Apparently the barrel shape of the spring keeps forces linear to the direction of compression minimizing any side forces. Amazing how something that seems so minor can have such an effect on how things act mechanically.

    Test Crown/Yoke

    testCrownYoke.jpg

    The "at rest" vs "compressed" differences are a little hard to see in the images. There's probably a half inch spring travel back and about three quarters of an inch dip at the front point of the frame.

    At Rest / Compressed Side View

    sideAtRestCompressed.jpg

    At Rest / Compressed Front Three Quarter View

    frnt3qtrAtRestCompressed.jpg
     
  8. The Renaissance Man

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

    Joined:
    Nov 24, 2012
    Messages:
    7,116
    Location:
    The Tropics of Alabama
    Glad it works!
     
    tjwilson likes this.
  9. Dr. Tankenstein

    Dr. Tankenstein

    Joined:
    May 20, 2009
    Messages:
    5,618
    Location:
    Marietta, GA
    I knew you’d find a simple/stylish solution.
    Really looking forward this one continuing.


    Sent from my iPhone using Tapatalk
     
    tjwilson likes this.
  10. tjwilson

    tjwilson Pro Member

    Joined:
    Jan 15, 2016
    Messages:
    359
    Been busy working on finishing up final frame and fork details.

    Rear Brakes

    Aligning and tack welding cantilever brake posts.

    rearBrakePosts.jpg

    A couple shots with the brake levers. I've read that center pull cantilever brakes aren't the best because of the angle that the cable pulls from. More up and away then pulling the pads in towards the rim. I've kind of made the situation worse by setting up the levers to reach in, past the tire width, to hit the rim with the pads. Haven't tested them yet but I suspect they may only offer a suggestion of slowing down. I think I'll be glad I'm using a disc up front.

    rearBrakeLevers.jpg

    Rear Brake Cable Stop

    rearBrakeCableStop.jpg

    Rear Cross Brace

    rearCrossBrace.jpg
     
    Scribble, léocwc, RustyGold and 2 others like this.
  11. tjwilson

    tjwilson Pro Member

    Joined:
    Jan 15, 2016
    Messages:
    359
    Kickstand Mount

    Drilled a hole in the bottom of the frame, welded in a nut, cut off a mount from a donor, and welded that in place. Side benefit is that the mount plate should help strengthen the chain stay / frame connection.

    kickStandMount.jpg

    Side Frame Additions

    I needed to stiffen the frame, there was just too much flex even after completing all tack welds. I had been putting this off because I wasn't exactly sure there wasn't a better solution. I even tried tack welding a temp straight bar across the bottom of the frame that tied into the bottom bracket. That didn't work, the frame really needed the second side curves. In the end I'm pretty happy with the look of the added tubes. And, they've eliminated the excessive flex.

    frameSideAdds01.jpg

    frameSideAdds02.jpg

    frameSideAdds03.jpg
     
  12. tjwilson

    tjwilson Pro Member

    Joined:
    Jan 15, 2016
    Messages:
    359
    Front Tire Clearance

    The front cross bar on the forks ended up too low and required a clearance notch. I ground clearance into the tube and welded in a curved piece to fill the resulting hole.

    frntTireClearance01.jpg

    frntTireClearance02.jpg

    Front Brake Caliper Mount

    I used the pad adjustment screw to clamp the caliper to the disc. I then created a template and cut a mount out of 3/16" plate.

    frntCaliperMount01.jpg

    frntCaliperMount02.jpg

    frntCaliperMount03.jpg
     
  13. tjwilson

    tjwilson Pro Member

    Joined:
    Jan 15, 2016
    Messages:
    359
    Final Springer Crown

    This ended up being very similar to the test piece that I made earlier. Just a little thinner with closed ends and a couple rounded corners.

    springerCrown01.jpg

    springerCrown02.jpg

    springerCrown03.jpg
     
  14. The Renaissance Man

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

    Joined:
    Nov 24, 2012
    Messages:
    7,116
    Location:
    The Tropics of Alabama
    The bike is looking good, but I couldn't help but notice the nice looking fence rails also!
    [​IMG]

    As always, it's fun to watch your builds. Keep 'em coming!
     
  15. Chad T

    Chad T

    Joined:
    Sep 7, 2014
    Messages:
    2,751
    Location:
    Columbus OH
    This is really coming along nicely. Front brake should stop you well if the rear doesn't but you could move the bosses in or use a wider canti to get more power. Hopefully it's like the springer and not as much of an issue as it appears to be....but it's an amazing piece of art even if it doesn't do a skid.
     
    tjwilson likes this.
  16. tjwilson

    tjwilson Pro Member

    Joined:
    Jan 15, 2016
    Messages:
    359
    Wider levers would be an easy switch if it's a problem, hadn't considered that. No skids would save on tire replacement costs though!
     
    Chad T likes this.
  17. GuitarlCarl

    GuitarlCarl

    Joined:
    Sep 14, 2013
    Messages:
    5,302
    Location:
    Bradley Illinoiz
    AHH, but are those handlebars wide enough for you to fly through them when the front wheel locks up?
    All kidding aside, discs on the back would really be ideal but a costly change at this point in the build.
    Looks friggin' awesome no matter what you decide.

    Carl.
     
    tjwilson likes this.
  18. tjwilson

    tjwilson Pro Member

    Joined:
    Jan 15, 2016
    Messages:
    359
    Thanks. Yeah, hopefully I won't regret not putting a disc on the back. No room to make it through the bars so I should probably practice my forward summersault dismount technique.
     
    Chad T, Troyminator and GuitarlCarl like this.
  19. JNOACK

    JNOACK

    Joined:
    Aug 26, 2016
    Messages:
    180
    Just wow! I've been so busy I haven't checked this in a while. I'm going to come back and read it all very closely as soon as I get my bike done. Great work!!
     
    tjwilson likes this.
  20. CRASH

    CRASH

    Joined:
    Jun 11, 2012
    Messages:
    4,308
    Location:
    Visalia, CA
    This is really something special! I've thoroughly enjoyed watching this come together, and all the little details. I can't wait to see the finished product!
     
    tjwilson and Chad T like this.

Share This Page