(MBBO#05 Class 2) Flashback GT - Done!

tjwilson

Pro Member
Jan 15, 2016
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A weekend spent whittling metal and trying to coax tight fitments between tubes. Doesn't look like a whole lot of progress. Baby steps, but all steps are going forward so far. Also picked up a seat and a couple hi-rise handlebars at a local swap meet. The seat upper and lower pans will provide a good start for the final seat. As for the bars, I had been thinking of modifying a set of drop bars to hi-rise. The ones I found will provide a good back-up if I run out of time plus, the price was right.

headtube06.jpg


headtube07.jpg


headtube08.jpg


fitment01.jpg


fitment02.jpg


fitment03.jpg

fitment04.jpg
 
Jan 9, 2013
1,251
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Los Angeles
Killer fitment. You have patience for sure... i tend to cheat short taper grafts just to avoid the amount of time... but the outcome is worth it.. very cool.
*edit... get it finished with a tig and leave the welds... no reason hide that kind of work! Itll lool slick regaurdless and gives other fabricators something to stop and drop jaw at ;)
 

tjwilson

Pro Member
Jan 15, 2016
523
2,196
58
Killer fitment. You have patience for sure... i tend to cheat short taper grafts just to avoid the amount of time... but the outcome is worth it.. very cool.
*edit... get it finished with a tig and leave the welds... no reason hide that kind of work! Itll lool slick regaurdless and gives other fabricators something to stop and drop jaw at ;)
Thanks! I know there's going to be a lot of stress in that area. Figure if I have a tight fit I'll increase the odds of getting at least a couple areas with strong welds. I'd love to get into TIG. There's even a maker space nearby that I've used in the past for powder coating. Like a club membership with training and every kind of metal working machinery imaginable. Some day.
 

tjwilson

Pro Member
Jan 15, 2016
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A little more progress on the frame backbone. A few molten metal caulk gun (MIG) weld close ups. Should probably spend some of my fitment time doing a few more practice welds.

weld01.jpg


weld02.jpg


weld03.jpg


Overview of the jig setup I'm using. Managed to keep things surprisingly straight.

frankenjig.jpg


Initial clean-up of the welds. Didn't want to spend too much time till I prove out some of my design assumptions. Need to make sure everything will actually be strong enough before making it look pretty.

weldcleanup01.jpg


weldcleanup02.jpg


weldcleanup03.jpg


Bottom bracket prep and fit.

bb01.jpg


bb02.jpg


MTB rear that will be donating pieces for the chain/side/seat stays.

reartubing.jpg


The ambitious plans for the weekend are to end up with a rolling frame!
 

tjwilson

Pro Member
Jan 15, 2016
523
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I like your jig set up. Looks like you have some nice curvy tubing for your rear 'triangle'....although using the word 'angle' on your build is a stretch! :bigsmile: Everything flows nicely!
Thanks. For the price of a few pieces of 1x1 tubing and some clamps the jig seems to be working well. The proof will be once it's standing on it's own with the wheels.
 

tjwilson

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Jan 15, 2016
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Things didn't go quite as quickly as hoped this weekend. Got about a third done of what I planned. Not a real surprise, pretty much typical. Here's some detailed documentation of minor progress ;)

Rear triangle chop and straighten. Needed to reduce the distance between chainstay sides by about an inch. Dimpled the sides a little in the process but those will be easy to fill later. Top left is before, top right after, bottom in process.

chainstayBend.jpg


Template for dropouts

dropoutTemplate.jpg


Dropouts

dropouts.jpg


Positioned in jig

droptoutPositioned.jpg


Chainstay to BB connection

chainstayBB01.jpg


chainstayBB02.jpg


chainstay.jpg


Fitment still needs a little finessing. I'll probably add a small gusset to each side to help strengthen it up.
 

tjwilson

Pro Member
Jan 15, 2016
523
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Had the chance to get some work in yesterday. Still need to fabricate the side / seat stays but, here it is to date.

Bottom bracket and dropout welds.

weld01BB.jpg


weld02Dropout.jpg


Frame pulled from the fixture.

frameInProcess.jpg


With wheels and checking for straightness.

sideRearview.jpg


A couple shots with handlebars.

threeQTRviews.jpg
 

tjwilson

Pro Member
Jan 15, 2016
523
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The chain stays required a little massaging for sprocket and crank clearance.

Sprocket interference.

sprocketInterference01.jpg


Added a dimple with a small section of half inch tube and a hammer while the chain stays were clamped and backed.

sprocketInterference02.jpg


Left crank interference.

leftPedalInterference01.jpg


Flattening chain stay with clamp and piece of 2x4.

leftPedalInterference02.jpg


leftPedalInterference03.jpg


Overview of clearances. Should be okay if I don't use too many layers of paint!

clearanceOverview.jpg


Side view with crank, sprocket and chain.

sideviewDrivetrain.jpg
 
Jan 9, 2013
1,251
1,541
Los Angeles
It really gorgeous... I do think it'll triangulate well with the seat pan and other bars.. a few gussets and it'll displace effectively..
I'd be more interested in how the stays deal with all those dimples.. from my understanding of the draft, it seems like there would be a great deal of torque going on down there at all times, I don't have experience with how they would perform because the wall structure in my mind is "compromised". I'm no used to building at this scale..
On a Harley that would be a fatigue point so it's a no no..
But it's a bike and not vibrating itself to death constantly also :bigsmile:..
Regardless I'm in awe:)... It's a beauty