Instructables
Picture of Bare Bones Bicycle Fork Jig
jighorz.jpg
In the spirit of my other framebuilding Instructables, here's a simple design for a jig for building forks. It's such an obvious design there must be others out there like it.

This jig is easily made from 8020 extrusion and connectors. The rest of the small parts and materials are all available from McMaster Carr. For tools you will need at least a drill press, drills, and some metric taps.

Yes, I know that's a carbon fork in the picture. Shame on me. It was close by when I took the picture.

Step 1: Tools and Materials

Materials:

1 - 8020 #1530L extrusion, 24" (28" if you're building 29er suspension-corrected forks)
1 - 8020 #1530L extrusion, 6"
2 - 8020 #4350 4-hole 90deg Joining Plate
1 - 8020 #3330 Universal Pivot Nub
4 - 8020 #3879 Economy Double T-nuts, M8
15 - M8 x 16mm button head socket cap screws (8020 #3813)
15 - M8 washers (8020# 3860)
1 - M6 x ~20mm socket head allen screw
2 - M5 x ~10 pan head allen screws, like used on SPD cleats
2 - M5 by ~10 socket head allen screws
1 - 1"x1.5"x1/8"t rectangular aluminum tubing, about 2"
1 - 1" (or close) aluminum round bar stock - about 6"
1 - Aluminum V-block McMC# 20065A8
1 - Toggle clamp McMC# 5126a17
1 - front axle from junked hub
4- axle locknuts from junked hubs

Tools:

Drill press or milling machine
Calipers
Layout fluid (optional but helps)
M8 tap
M6 tap
M5 tap
Countersink bit

McMC = McMaster Carr

8020 = 8020, but they sell through local distributors. Check their website for the nearest distributor. If you can't find one nearby, I can heartily recommend F & L Industrial Solutions.

Step 2: General Game Plan

Picture of General Game Plan
Here's the general plan:

1) modify the pivot piece to turn it into the dummy axle
2) tap the end of the shorter piece of extrusion and mount the dummy axle
3) modify the v-block to mount the clamp
4) prepare the Park stand mount
5) drill the access holes in the main extrusion beam
6) assemble the jig
7) align the V-block
 
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mikepearson2 years ago
I really like the simplicity of the jig, having just used an anvil jig on a frame & fork building course.

Once the fork crown, steerer and legs are brazed I presume you can just braze the dropouts on without too much of an issue with distortion? Do you just lock them in place on the dummy axle with some big old nuts?
drwelby (author)  mikepearson2 years ago
I put the dropouts in the legs first.
proparc6 years ago
The spirit just hit me again. You could use the same 8020 piece that holds the front axle because it already has the 2 counterbored holes for the 2 channels. Simply slide it back and forth to register the blades, quick line up with a T square and walla! Granted not everyone is into registering the fork blades, but it's just a suggestion for those of us who do.
proparc6 years ago
drwelby, you did it!! I caught your act over at Frameforum.com. You are the man!! A simple attachment to "register" the fork blades should easily be attached somewhere along the center. In fact-hold on, I feel the spirit of Autocad coming over me again. Because there is no center channel,how about a block with a, say a 45 degree slope on top. As it moves back and forth along the 2 outer channels in the main extrusion, it would register with the slope in the fork blades. Easy peasy lemon squeezy.
Mexicoman6 years ago
Nice alignment jig. I doubt many folks realize all the geometry that goes into bicycle and motorcycle forks or how the rake, caster and trail effects handling. In my reckless youth, I had a shop that straightened motorcycle frames and forks after light collisions. We charged quite a lot because of the difficulty in checking accuracy of the alignment, not necessarily the work of pushing metal around with hydraulics. Although we were expensive, we were still 40% to 60& below that of complete frame replacement. I very much like what you have done. Welding causes heat, and heat distorts and warps metals. You need a positive lock jig to retain the positioning you desire while welding an cooling takes place. Very fine instructable. Well done!
leebryuk6 years ago
Nice Job. How well do your forks hold up for? I always have that fear a set of forks will leave the party on me. I am interested in building my own bike in the future. I avoided carbon for years thanks to the early poor quality control. Seems to be fixed though. Good job, and keep the bike stuff coming. Lee
Doctor What6 years ago
what's this for?? sry to sound stupid.
drwelby (author)  Doctor What6 years ago
It's a jig to hold the parts of a bicycle fork in alignment while you braze or weld it together.
oh...
Lftndbt6 years ago
Nice design! :)