Custom built fork fixture on a budget

June 22, 2010 · 3 comments

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The front fork fixture is complete and works alright. It took awhile to figure out how to build but I think I can re-use it for many projects to come.

The fixture has to hold the fork such that all the critical points are in line with each other for brazing. There are production fixtures available but I’m building electric bikes on a budget so I have to make my own fixtures to save money. The fixture in the photo was built using parts I had around the shop so it was basically free except for the time it took to create.

The front fork presents some interesting alignment issues. There are multiple alignment points that must be as close as possible such that when the wheel is installed it is equidistant between the fork blades and is in line with the steering column. The fork blades must also be parallel to each other so that it is not twisted. The dropouts must be held at the correct height and level and the correct distance apart. It’s like a 3D balancing act. The fixture holds all of these alignment points while the dropouts are brazed. It will also hold the fork blades while brazing them in the crown as well. In my case I was just chopping a pre-built fork so all I had to do was braze the dropouts.

Building fixtures is a great way to learn how to build a frame and fork. It makes you think about the important alignment points. However, even with the best fixture, alignment is not guaranteed. Metal when heated expands and changes structure. This can cause alignment issues during and after brazing or welding. There is no substitute for alignment checking throughout the build process.

{ 3 comments… read them below or add one }

1 Gene June 22, 2010 at 3:17 pm

Yes, alignment issues with the forks are always a big issue. I often take my bike apart to store it and realigning the handlebars with the forks is always guesswork. Is there any way you can make some guide marks that would be incredibly obvious to even the most casual observer in reassembling the bike. Great work. gene

2 pdxebiker June 22, 2010 at 4:16 pm

Nice job, Dan! It’s great to get insight into how frames are built. I’m eager to see what you’re doing with the ShortHopper concept!

3 Dan June 22, 2010 at 9:41 pm

@Gene – The way I like to line up the bars with the fork is to lay a straight edge across the forks without the wheel. Sight down the bars to the straight edge. If they look parallel, its aligned. This is easier than trying to sight the wheel perpendicular to the bars.

@pdxebiker – Thanks. Building frames is very satisfying. Stay tuned for more ShortHopper. The geometry and drawing are complete. Today I chopped an old frame to get it ready to reassemble. I’m still trying to decide what ebike kit to use.

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