5. Frame stretch and rake...

A blow by blow photographic account of chopping from stock to chop... This projcet has been given its own forum due to the large number of photos it contains making uploading slow for those of you still on "dial up".
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Prof
Founder, Choppers Australia
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Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
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5. Frame stretch and rake...

Post by Prof » Mon Nov 06, 2006 10:12 am

Chopping frame to add some rake... That's why its called a chopper baby!

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Step 1... set bike on blocks to get correct height (allowing for weight of motor and rider to drop bike ½")

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Step 2... Mark and cut down tubes and top tube. Use a tube cutter to mark cutting line. This ensures your cut will be perpendicular.

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Crikey. Did we really want to do this!!!!


Step 3... Mount front end with extended forks (ours are 4") onto cut off section and sit against rear of top down tube. This will show us how much extra length we need in front down tubes (forgot to take a picture of whole set up... sorry). .

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Slugs for down tubes are 55mm. Tack welded them into bottom down tubes. Can now sit top down tubes back on and bend steering head back so to tube can be rejoined. these slugs are solid and will be preheated at time of final welding. Alternative is to drill them out so they are about 3 times wall thickness of down tubes. this is to ensure strong welds.

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Cut part way through tubes just under steering head assembly to provide a nice sharp and unobtrusive bend.

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Bending done, check degrees of rake. Stock was measured at 30. Now will be 36 degrees

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Here's slug to rejoin top tube. Tubes meet at a 5-10 degree angle so linished a bit off bottom of slug after turning it lathe. Slot in top of tube is so we could retract slug all way into tube to allow other half to to line up. Drilled hole in top of slug is to allow us to push it forward into position. All slugs will be welded around join and then plug welded.

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Before final fitting Michael cut off ugly fork stop set up and any other protrusions as well as welding up a number of holes no longer needed.

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Frame is tack welded and tried for size. Not bad! What we've done so far to frame has increased wheelbase by about 5".

This will make a significant improvement to stability and ride. Six degree rake (30 to 36 degrees) on this bike has increased trail by 1 3/8" from 4 1/4" to 5 5/8 "which means steadier steering. Safety on the road is increased as wheel is both harder to deflect when hitting an unexpected object and returns to its original line more definitely and quickly.

Advantage?... less riding effort and greater likelihood of staying upright when hitting the inevitable gravel on a corner or unexpected lump of wood in one's path.

This stabiltiy at cruising speed means slower handling at low speed so less speed around roundabouts and T junctions, but lane changing is not affected. If alignment is maintained by careful constrution, you can sit back no hands at any speed above 40kmh...
Chopit'nrideit... Prof

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