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Framebuilders Thinking about a custom frame? Lugged vs Fillet Brazed. Different Frame materials? Newvex or Pacenti Lugs? why get a custom Road, Mountain, or Track Frame? Got a question about framebuilding? Lets discuss framebuilding at it's finest.

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Old 01-29-12, 02:42 PM   #1
john hawrylak
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Bend of the Fork

How is the bend in the fork specified for a nice looking curve?? Is it up to the individual frame builder or are there standard curves that look nicer than simple bend in the fork in 1 location?? Looking for a custom frame fork with low trail front geometry and approximately 63 mm offset. With that much offset, the shape of the fork bend needs to be considered.

There are 5 examples I can think of.

1. I know Grant Peterson at Rivendell makes a point of how nice the A Homer Hilsen fork is bent AND the bend costs more than a standard bend. The AHH fork bend is somewhat nicer than the Sam Hillborne.

2. The mid 70’s Paramount Touring forks have a nice bend to them. Nicer than the lower price models.

3. The line drawing of a French model in BQ Winter 2011, Overview of Frame Geometry, has a nice bend to it.

4. The Velo Orange Rando frame has a sharp bend at one location and is not a nice looking as the above.

5. Higher end Raleigh’s seem to have nice curve in the fork.

What makes for a pleasing curve and how does one specify it for a custom fork with an offset of approximately 63 mm??
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Old 01-29-12, 02:57 PM   #2
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I'd say there are three "basic" kinds of bends. The most common is probably the "continental" style where the blade is gradually curved, starting from about the midpoint of the blades. Then there's the French/British style where the bend is sharper and occurs primarily in the lower third or quarter of the blade. And then there's the "kink" which is just a short, sharp bend about 3/4 from the top, with a straight section above and below the bend.

Most builders and most benders make the Continental bend. It's easy to make. The Brit/French bend is tougher, especially once you get into the 6+ cm. neghborhood. The blade has to be well supported, or it will collapse. I went through a number of iterations (and blades!) before getting it right. And, due to a recent "improvement" in my jig, I've now made several "kinked" bends, which work fine but really look cheap. You'll find the same "kink" on lower priced (but still good quality) stuff from Asia, like the older V/O forks, because it's the easiest bend to make, especially if you're using a machine to make a hundred at a time.

IMO they're all about equally functional. Jan/BQ believes that the British/French style is the most comfortable and has pretty convincing numbers to back it up, but I personally can't feel a difference. I think 95% of ride comfort comes from the tires.

So IMO fork bend is all about aesthetics. Most people seem to like the Continental bend, if they think about it at all. With the resurrection of the French rando stuff, the Brit/French bend is coming back into vogue, and I personally think it's the best looking. And of course, the mass-produced "kink" blades that most people (well, the few people who give a rat's ass about any of it) find ugly.

How do you ask the builder for what you want? In plain English, I guess. If someone came to me and said "Hey, I want a fork with a tight bend at the bottom, like Singer used" or "I'd like one of those long bends like I had on my old Bianchi road bike" then I'd know just what he wanted. And, as always, a picture is worth a thousand words. A photocopy of that French line drawing doesn't leave much room for error on your builder's part...
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Old 01-29-12, 03:33 PM   #3
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For me, a visually appealing fork is one where the curve extends all the way to the dropout. It's much easier for manufacturers to rake the blades after brazing them into the crown, but this results in a straight section between the dropout and where the rake begins:



In order to get the curve to extend all the way to the dropout, the blades are raked before brazing, and the straight section remaining at the dropout end is trimmed off before attaching the dropouts:



The radius of the bend may be large, as above or smaller:

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Old 01-30-12, 09:23 AM   #4
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To add some numbers to the above good info, typically the bend radius for the gradual "italian" bend is about 12 inch. For the nice French or British bend, the radius is some sort of gradual compound 5-6-9 inches curve.

Six jours I made my mandrel out of a slab of spruce, with a hand-filed groove. Radius is compound 5-6 inches. Seems to work allright but I haven't tried a rake bigger than 6 cm.
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Old 01-30-12, 10:15 AM   #5
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it's not so much the radius, but as John says, where the radius ends. To most people, a good looking fork has radius ending at the dropouts, not 50% of the way up the fork. From a functional viewpoint, it's not so important
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Old 01-30-12, 10:41 AM   #6
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If you want to go the route of making a bending jig, I made mine by using two pieces of maple, cutting the curve I wanted, and putting a 45 degree chamfer on the inside faces with a router. I then glued them together. To me, that was easier than filing the groove. Depending on the tools you have available, a bending jig is easy and fairly cheap. If you donate it to your framebuilder, he might even cut you a deal on the fork.
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Old 01-30-12, 12:29 PM   #7
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I made my jig from aluminum jigplate.
Instead of a simple radius, the bending form has an involute curve. This results in a "continental" style bend with a uniformly decreasing radius to the dropout.
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Old 01-30-12, 12:40 PM   #8
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Aesthetically, I prefer a larger radius bend. Nova sells the Hammill Engineering fork raking tool which comes standard with a 10" ramp, but an 8" ramp is available as an option. I went with the 10" ramp because like the more graceful curve of the larger radius.

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Old 01-30-12, 05:58 PM   #9
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Thanks to all the posters, very good info and J Thompson's & Stans pictures were great.

2 follow up questions:
1. John Thompsn's pictures #2 ans #3. #2 appears to be a Continental bend and #3 appears to be a French/Brit form Six Jours classification??? Also, is #2 appears to be a longer radius???

2 Aesthetically, it seems preferable to have the tube bend all the ways to the drop out as Unterhausen stated and Stans picture shows??
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Old 01-30-12, 06:31 PM   #10
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Quote:
Originally Posted by john hawrylak View Post
1. John Thompsn's pictures #2 ans #3. #2 appears to be a Continental bend and #3 appears to be a French/Brit form Six Jours classification??? Also, is #2 appears to be a longer radius???
IMO.

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Originally Posted by john hawrylak View Post
2 Aesthetically, it seems preferable to have the tube bend all the ways to the drop out as Unterhausen stated and Stans picture shows??
Well, I think so, and a lot of other folks seem to think so. But isn't that kind of like asking if blue is an aesthetically pleasing color?
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Old 01-31-12, 06:32 PM   #11
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curvaceous

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Originally Posted by Scooper View Post
Nova sells the Hammill Engineering fork raking tool which comes standard with a 10" ramp,
but an 8" ramp is available as an option.
sweet.
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