Fork build questions
So I've been daydreaming about building a fork for a while. I've got a fork crown from an old Bontrager mtb fork. Maybe its a Tange Switchblade fork crown, I'm not sure. They're both essentially the same thing. They were straight blade, tapered and very elegant. I would like to build a semi-replica of these super cool forks but with a twist. I'd like to build it to accomodate touring needs. In other words, I want dual eyelets, cantilever mounts, and mid-fork lowrider mounts.
Anyway - Been looking at stuff at Nova Cycle Supply and am a little confused.
My crown measures 1" (25.4mm) with a dial caliper where the round tubes bolt into it. The only round, straight fork blades are called out as 24 mm x .9mm x 390mm long. The smaller end measures 12.5 mm with 1.8 mm wall. 290mm long taper: http://www.cycle-frames.com/bicycle-...ACK-ROUND.html
The dropouts I'm considering are these: http://www.cycle-frames.com/bicycle-...-W-2-EYES.html
12 mm plug, 14 mm lip.
My questions are these:
Is the fork tubing measured on the ID and wall thickness or OD and wall?
If it is called out based on ID, then I may be in luck. The dropouts with their 12 mm plug will fit right into the end of the fork. The large end at 24mm ID (presumably) and .9 mm wall gives an OD of 25.8mm. Of course they would have to be cut to length (fitting to a 1985 Peugeot Canyon Express MTB) and kitted out with canti bosses and the lowrider mounts, but overall this should be a really simple build if the fork blade dimensions are measured on the ID of the tube.
The dropouts plugs will have .5 mm clearance for braze material to wick into. Is this an acceptable joint thickness for safety's sake?
Lastly, will these be durable enough to be used in a touring type application? I don't know when I'll ever actually take a tour, but the bike is in the process of being converted over with that end in mind.
I have a highly accomplished welder here and I have utmost confidence in his abilities to do a good job.
I've never done this kind of work before so if I'm waaayy off base let me know.
One other thing: Where the fork bolts into the crown is the thinnest of the material. I'm a little leery of this so was planning on brazing in some reinforcement to the ID that would extend maybe 1-1/2" to 2" into the ID. Is this a good or a bad idea. I can spin something up in a lathe to be a very close tolerance fit......
Last edited by Smokinapankake; 02-02-12 at 03:47 PM.
Reason: Added info
don't you need to sleeve the outside of a round blade in order to have it fit your crown? I have seen a discussion of these forks recently, I think you can still find the blades occasionally.
The plug style dropouts are a bit of a thesis. You have to find a point on the taper of the blade where they fit inside. So with the dropouts you have chosen, you will have to cut some part off the small end of the blades. You can also mount the dropout in a lathe and reduce the size of the plug. I have done this and it works ok.
I am not familiar with the fork you want to use. If it is not required to rake the blades, I would use constant diameter tubing and use plate style dropouts like is generally done on segmented mtb forks. For example, see this post The finished blade is in this post
Henry James sells 1 inch diameter fork blades that are tapered in two different wall thicknesses from True Temper.
25.4 Round Priced Per Pair
1.0/.7 14.0 V 422 KIT-FB-7 $26.90/pr|$25.80|$24.20|$19.85 428
1.3/.9 14.0 V 422 KIT-FB-4 $21.35/pr|$20.50|$19.20|$15.75 596
So are they measured OD and wall thickness?
I'd considered finding a pair of legs to replace with but the down side is that they did not feature any eyelets on the dropouts nor did they feature a mid fork lowrider braze-on.
I prefer the look of a tapered fork; those large diameter constant diameter forks look clumsy to my eye.
Thanks for that info about Henry James; I'll have to look around their website to see what is available. Would like to get it all at once if you know what I mean....
yes, OD and thickness. As I mentioned, you have to figure out how much of the taper to cut off to match what you want the plug to be
Originally Posted by Smokinapankake
Thanks for the help; it may be a little while before I get some time to go forward with this project. There will be photos when I do, though!