Hi
I am drawing my first bicycle frame,
When i draw the fork, its parts including crown and headset.
How do you know the detail size of those parts?
Should I need to buy all parts before I draw frame?
I will build frame by TIG.

thank you!

Knowing the actual parts' dimensions is step #1 . Saying that it is very possibly to draw most all of the important frame aspects without the crown, bb shell, tube diameters, etc. After all it's really about the body's contact points first. But until the real parts' sizes are included the plans are only body specific.

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Paragon has engineering drawings of their parts on their website. Otherwise, you are on your own, and actual parts are a really good idea

OK I know what to do.
I will buy parts first!
Thank you!

Lacking a jig to bend the blades, of the finished fork. , get an angled fork crown to use straight blades..