Saturday, 8 October 2011

Numbers and the Frame Jig

I have now done enough research on the frame to be happy with my chosen figures, the dimensions have chosen are ones that I either know to work, or are features fom other bikes I have ridden that I liked and wanted to incorporate into my own design, or are more feasible for me to construct with fairly basic engineering tools as most of the build will be in my shed. Welding it will most likely be done at my dads workshop though as there is a TIG welding set there and that opportunity shouldn't be missed.

The angles I have chosen are in my first blog, but here they are again, all inches and millimetres
Head Tube Angle - 65 degrees
Seat Tube Angle - 74 degrees
Wheelsbase - 45 inches/ 1143mm
Chainstays - 17 inches / 432mm
Front Centre - 28 inches / 711mm
Seat tube - 16 inches / 406mm
Rear Wheel Travel - 6 inches / 152mm
Shock Stroke - 2.25 inches / 57mm
Pivot to Rear Axle - 20 inches / 508mm
Pivot to Shock mount - 7.6 inches / 193mm
Pivot Location - 3.9 inches / 99mm above line of wheelbase, 5 inches / 12.7mm outside the BB centre
BB Height - 0.25 inches / 6.35mm below line of wheelbase

Did a cleaner Drawing of the main points on the design

Frame Drawing, done with Pencil, Ruler and Protractor, No CAD here

Once i knew what size and shape it was going to be i could then set about making up a jig. Jigs are needed to ensure that things go together in line and to the shape they were designed. i proably could do it freehand, the stuff i make at work isn't jigged and my angles have to be +/- 0.3 of a degree which i ahchieve regularly, when you consider a top end frame like the trek session 88 is only done to 0.5 degree tolerance it gives you some perspective.

My jig needs to hold the following parts tightly in position, in a way that still allows access for a welding torch:
Head tube, Seat tube, Bottom Bracket and dropouts once the swingarm is welded up seperately. this will need its own jig. WORK!
So here are the pictures of the finished article:
Full jig

Full Jig on kitchen floor.

Fork length Adjustment, currently set at 546mm for a Marzocchi 55 set at 160mm travel

Fork height adjustment via an old boxxer crown

BB clamp piece. think I'm going to revise this as it isn't how I really want it

Rear Dropout jig holder. this is part i'm pretty happy with. is simple, square and goes about its job quietly

 I put my hardtail frame in the jig just to alignment check it. Everything seems good.

And again led down, just to show off the angles and how it goes in.

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