Omiak

So I'm planning to build a frame designed around 451 (20") wheels. I was hoping to build a lugged straight blade fork as this seems to be an easier route than building a fillet brazed fork.

I was looking at this set of fork blades (with a lugged crown and socketed dropous) when I realized that the taper length is a few cm longer than the blade length that my design requires.

NOVA CRMO ROAD Fork Blade 24mm Oval 0.9mm Wall :: TUBES STEEL :: Nova Cycles Supply Inc.

I'm assuming that if I cut into the taper on either end I'm going to have problems getting the fork blade to fit properly into the crown socket or dropout socket. I've been looking for other fork blades but I'm finding that most don't list the length of the taper. Does any framebuilding supplier make fork blades designed for smaller wheels (maybe a recumbent or bmx set would work?) Would it be best to just build a fillet brazed fork? Could I maybe get away with using the lugged for crown and brazing in slot style dropouts?

For reference here's a rough mockup of the design I'm working on:

Adroit Track Minivelo | www.bikecad.ca

Any advise would be appreciated.

Thanks.

zandoval 

Is this the problem? I am not sure I understand...

tuz

I've built two forks with 20x2.0" (ISO 406) wheels, so roughly the save size if you have small tires. I used plate dropouts (slotted blade) and trimmed as much as possible on the small end. It was close. And I used curved blades, which adds a bit of length.

I'm not aware of shorter tapered blades (290mm seems standard).

You can also make a double plate crown and fillet it, but it's a lot of work. Using a sloped crown will save you some length.

Omiak

Yeah, those blades are 390mm long but the tapered part (the part that gradually changes size) is 290mm. My design calls for fork blades that are less than 265mm in length. If I cut into the part where the blade is tapering then I assume I'll have an end that is either to small to properly fit into the crown, or too big to properly fit into the socketed dropout (depending on which end I'm cutting from).

Live Wire 

Yeah, I doubt you'll be able to use the socketed drops on this if you want to use a lugged crown.
Just use plate drops like tuz suggested.

Omiak

Sounds good. Thanks for the help you guys.

unterhausen

You can cut almost 4 inches from the un-tapered part of the crown before it doesn't fit into the crown. Your problem would be getting a dropout to fit, but there are some pretty wide plate style dropouts. Socketed dropouts are a pain to deal with anyway, and in your case it isn't going to work.

BenCooper

I make 16" (349) forks using Columbus SL0I16V1 blades from Ceeway - I chop a bit off the bottom end and use 12mm plug dropouts.

duanedr 

Can you cut from both ends of the blades and get where you need to be? 100mm from the top and 30mm from the bottom should get you close enough to use the plate dropouts.

MassiveD

Usually you can cut some from the top since there is parallel material up there also. You have to consider the effect on fork stiffness, the trim from the top will give a fork that is less stiff, and the trim from the tip will lead to a fork that is stiffer. You would stay better within the parameter of stiffness set in a longer blade set, if you trimmed everything from the butt, of course you have your issue there.

Bike Fridays are said to be made out of conventional seat stays, which suggest the idea of butt trimming if you imagine what would be left after significant butt trimming.

Of course, if you are using reasonable tires, say 32s or 35s, stiff blades may not be a problem, and BMX blades can be radically stiff. One local store sells them, and they are built like tanks, in a number of interesting configurations. The ones designed for multi level foot pegs are particularly intriguing for front racks on tourers.

BenCooper

I cut 55mm off the bottom of the Columbus blades. Short forks are going to be a lot stiffer than long forks anyhow.

MassiveD

That is why you don't want to make maters worse by triming from the tip. If it could be avoided.

BenCooper

Stiff forks aren't a bad thing necessarily.

Andrew R Stewart 

Especially if the tires are wider and use less then really high pressures. Andy.

BenCooper

Yes, though actually small-wheeled bikes often go the other way, with high pressure tyres. Then they have flexibility higher up, with suspension.