Shortbow

Discussion in 'BUILT FROM SCRATCH' started by tjwilson, Oct 15, 2019.

  1. The Renaissance Man

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

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    Good idea.
     
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  2. GuitarlCarl

    GuitarlCarl

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    It"s basically what that 350 dollar kickbender is...
     
  3. tjwilson

    tjwilson Pro Member

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    Thank you very much. When I first posted I realized I'd included an underscore in your username. I made a quick edit as soon as it went up. Probably why you didn't get an alert. I've barely started and can't wait to see how its going to run.

    I'm thinking I should be close, but okay, on clearance. You might be looking at the dimensions on the drawing? The bb to ground is actually just under nine and a half inches. The drawing shows the dimension to the top of the frame jig.
     
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  4. tjwilson

    tjwilson Pro Member

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    You've got the wheels turning for a version 2.0! Not only would sides help prevent crushing the tubes, they would also keep the tubing perpendicular to the bend. Great idea, thanks.
     
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  5. tjwilson

    tjwilson Pro Member

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    Tire Combo

    I've been struggling a little to get build time in on this. I did have time to mount and checkout the tire combination though. That rear tire is huge. It's also amazing how light it is, far lighter than it looks.

    01_tiresMounted.jpg
     
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  6. sandman

    sandman

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    Cool build . You should be able to float on water with those tires .
     
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  7. Chad T

    Chad T

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    Love that tire combo!:inlove:

    So 140 cranks are the same as a Fastback. Those aren't too bad actually. I was thinking that was the early Stingray size. 155 might be the sweet spot for crank size and there is a decent selection (lots of BMX) of those. 170 might be a bit long for the short wheelbase. Tempting though as 90% of 3 pc cranks come in that size.
     
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  8. tjwilson

    tjwilson Pro Member

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    155 might be better. I like the shorter cranks when riding the Fastback. Though when @OddJob originally suggested longer cranks I decided to go all out with the 170s. If I can squeak the frame past those I'll have plenty of room to switch out to shorter cranks later if I want.
     
  9. Psychographic

    Psychographic

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    Those wheels and tires are going to look so good on that frame!
     
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  10. léocwc

    léocwc

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    beautiful project:41:
     
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  11. tjwilson

    tjwilson Pro Member

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    Steering Tube

    Seems about half of the builds I do require either a shortening or lengthening of the steer tube. Sections of steel angle in a vise haven't failed me yet to keep everything straight.

    01_steerTube.jpg

    02_steerTube.jpg

    03_steerTube.jpg

    04_steerTube.jpg

    05_steerTube.jpg

    06_steerTube.jpg
     
  12. tjwilson

    tjwilson Pro Member

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    Seat Tube

    There really aren't many tubes that make up this frame. Good because it should be light(er). Bad because there's few places to hide a bend that might be a little off. The center/seat tube for this frame has a "J" bend to it. Took three attempts to get one I was happy with!

    01_tubesBent.jpg

    Upper and lower seat tube connection.

    02_seatTubeJoint.jpg

    03_seatTubeJoint.jpg

    The seat stem required a thicker wall tube than I wanted to use for the entire seat tube. I trimmed the bent tube and added a thicker wall tube section to the top. There isn't a lot of adjustment travel to the seat stem. I'm shooting to have just enough stem depth to securely hold the stem and adjust height, if needed, by trimming the stem from the bottom.

    04_seaTubeTop.jpg

    05_seatTubeTopDone.jpg
     
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  13. tjwilson

    tjwilson Pro Member

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    Top Tube

    I designed the frame so that the top tube attached to the seat tube pretty much the entire length of the stem depth. I'm hoping this will create a rigid enough connection to hold up to the leverage of the seat stem. Fingers crossed.

    01_topTubeAdd.jpg

    02_topTubeTacked.jpg

    Had to lean the mounted tires up against the fixture for a quick look.

    03_topTubeWtires.jpg
     
  14. OddJob

    OddJob

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    Nasa called, they want you to come back to your old job. :nerd:
     
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  15. tjwilson

    tjwilson Pro Member

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    :bigsmile:
     
  16. Psychographic

    Psychographic

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    I just love watching a mastercraftsman at work. This is definitely my favorite bike in the build off and it isn't even a full frame yet.
     
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  17. tjwilson

    tjwilson Pro Member

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    Chain-stays

    I showed them above in the overall bent tubing image but here they are again.

    01_initialBends.jpg

    This was how I originally intended to use these tubes. The first bend wrapping around the tire and slipping between the chainring and tire.

    03_originalOrientation.jpg

    On closer look this wasn't going to work. The frame is designed with the chain-stays kicked up towards the back and running downhill. I like the look but it causes interference with the chain if the tubes are left this way (circled the area in a top/side view drawing below).

    02_chainInterference.jpg

    I decided to rotate the tubes and add a new bend at the front to get the tube between the tire and chainring. This gave me chain clearance as well as let the chain-stay run parallel to the rear rotor. Should make it easier to create a bracket for a caliper when I get to that.

    04_revisedOrientation.jpg

    05_additionalBends.jpg

    This new bend doesn't quite slip past the tire and crank as well as the fist.

    06_preChainringClearance.jpg

    Did a little work with a hammer to flatten things out. I suspect I may be cutting the flat section out and welding in a new piece to push the tube back even more.

    07_postChainringClearance.jpg
     
  18. tjwilson

    tjwilson Pro Member

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    Rear Drop-outs

    Needed to finalize the drop-outs before going any further with the chain-stays. Made a template, traced that to a couple of sandwiched pieces of 3/16" mild steel, and cut and ground away what I didn't want.

    01_template.jpg

    02_ready4cutShape.jpg

    03_roughDropouts.jpg
     
  19. tjwilson

    tjwilson Pro Member

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    Back to the Chain-stays

    The diameter of the die for my tubing roller is just a little bigger than the tire cross section. Made for a great reference when fitting the chain-stays to the bottom bracket.

    01_fit2bb.jpg

    I used the hydraulic tubing bender to pinch the back ends of the chain-stays. Here's a before and after.

    02_preEndPinch.jpg

    03_postEndPinch.jpg

    Then trimmed to final length.

    04_cut2finalLength.jpg

    Gorilla and painter's tape fixturing.

    05_ready4tack.jpg

    Chain-stays and bottom bracket tacked up.

    06_tackedBBchainstays.jpg
     

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  20. MattiThundrrr

    MattiThundrrr

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    Like. Very like.
     
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