Shortbow

tjwilson

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Totally honored to even be mentioned in connection to this. That looks like a killer selection. 10 speed is a great way to go. Not as expensive as 11 and better selection than 9.

I like the idea of longer cranks with the gearing you have. You'd need a smaller front ring to make them little egg beaters fun. Can you raise the bb a bit to give you some more clearance?

Sorry it took me so long to chime in...must have been a snag with the tag. Never got an alert. Looking cool..:thumbsup:...dig the wheel/tire selection too.
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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tjwilson

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Well my friend, I have used a tool to bend offsets in thinwall electrical conduit. We always called it a kickbender and it would bend a "kick" in a stub so that the conduit running along a wall would offset into an electrical box. Looks almost identical to what you were trying to bend they only cost 2 - 300 bucks...
View attachment 108513
You could hand bend it with a conduit bender KOTA style, hand benders are cheap at 40-50 bucks, even cheaper at a pawn shop... But I think your tubing roller should be able to do that offset bend.
I too use duct tape to plug and salt to fill...

Hey I wonder if you could fab your die to include curved mandrel like sides made from pipe?

Carl.
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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tjwilson

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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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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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tjwilson

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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.
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.
 

tjwilson

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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
 

tjwilson

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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
 
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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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tjwilson

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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
 

tjwilson

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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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