Kirk Frameworks - Page 49

David Kirk · #**721** 11-08-2016, 05:25 PM

Seamless fork crown.

dave

Climb01742 · #**722** 11-08-2016, 07:49 PM

Damn, that's pretty. Simple and elegant.

sparky33 · #**723** 11-09-2016, 10:15 AM

Quote:

Originally Posted by Climb01742

Damn, that's pretty. Simple and elegant.

Exactly.

MRB · #**724** 11-09-2016, 02:05 PM

Hi Dave, I though that your preference was to NOT build unicrown forks? As they could be too flexy or not rigid enough? Can you elaborate?

None-the-less, that is a beautiful fork. Organic looking, just like your fillet brazed frames. Good work. A+

soulspinner · #**725** 11-09-2016, 03:39 PM

Quote:

Originally Posted by MRB

Hi Dave, I though that your preference was to NOT build unicrown forks? As they could be too flexy or not rigid enough? Can you elaborate?

None-the-less, that is a beautiful fork. Organic looking, just like your fillet brazed frames. Good work. A+

That one appears to have a stout top section...

David Kirk · #**726** 11-09-2016, 04:22 PM

It is not a unicrown fork and I still think unicrowns are a very bad design.

This is a traditional crown-and-blades set up but the crown is internal to the blades....so instead of the blade slipping into the crown the crown slides into the blade. If you look very carefully you can see the straight silver line that is the seam where the crown and blade meet.

This fork will be mated to a special fillet frame I'll be bringing to NAHBS this winter in Salt Lake City. I had a free afternoon being held up waiting for a shipment of stuff needed to build the current frame in the queue so I dove into this part of the show bike project.

UPS should be here any minute with the stuff I need to get back onto my customer bike and until then I'm going for a ride during our super rare 60° November day.

dave

weisan · #**727** 11-10-2016, 06:35 AM

so so smoooth...

Clydesdale · #**728** 11-14-2016, 04:57 PM

Outstanding!

Wakatel_Luum · #**729** 11-14-2016, 08:53 PM

I'm curious as to why it is thought unicrown forks are bad?

David Kirk · #**730** 11-15-2016, 10:44 AM

Quote:

Originally Posted by Wakatel_Luum

I'm curious as to why it is thought unicrown forks are bad?

The problem with a unicrown fork starts with how the blades are made. Typically they start with a tapered round tube and then bend it nearly 90° at the top so that it can properly meet the steerer. In order for the round tube to survive the bending process the wall thickness needs to be very thick otherwise it will wrinkle or collapse. When the tube is bent the wall thickness at the outside of the bend becomes a good bit thinner. So....you end up with a fork blade that is thicker and heavier than the needs presented by the rider and it's only that way so that it will bend during forming without failing.

The other thing that happens when you bend a tube is that it becomes ovalized in cross section.

This means that the upper part of the blade (area here it is bent) is oval in cross section making the tube less stiff laterally and relatively more stiff fore/aft. Combine this with the fact that the outer wall thickness of the blade was thin (making it less stiff sideways) and you get a blade that is stiff in the fore/aft direction, soft laterally, and otherwise heavier than need be.

So...compared to a lugged fork a unicrown is heavier, stiffer fore/aft and softer sideways. All downsides and no upsides. Well that's not really true. The upside is that a unicrown fork can be tig welded. But from a riding standpoint having a heavy fork that is stiffer than need be fore/aft and softer than it should be laterally is not a good thing.

Sorry for such a long answer - the coffee hasn't kicked in yet.

dave