1 of spring material
1 of sheet metal 3 1/16" x 3"
1 of 1/2" PVC nipple 6" length
2 of 1/2" PVC threaded caps
2 of #10-24 machine screws
2 of #10-24 hex nuts
2 of #10-24 wing nuts
4 of #10 washers
4 of pipe clamps
#10-24 Screw Tap
#10 sized screws were selected because they can fit crimpable ring terminals.
Step 1: Create Drilling Template
Using an index card and triangle tool:
1. Put the PVC cap onto the middle of the index card, don't worry about it being perfect.
2. Trace the cap around the index card.
3. Draw tangent lines perpendicular to one another around the traced cap circle.
4. Draw lines from corner to corner of the square formed by the tangent lines.
5. The intersection of these two lines is the center of the traced circle.
Step 2: Drill & Thread Cap
2. Center the template below the drill press bit.
3. Cover the cap with masking tape to prevent wandering.
4. Drill the cap with an appropriately sized bit at high speed, slowly push down.
5. With no power applied to the drill press, rotate the tap into the newly formed cap-hole.
Step 3: Cap Assembly
2. Use a screwdriver and wrench to attach the hex nut.
3. Slide on a washer.
4. Slide on the terminal ring / wire.
5. Slide on another washer.
6. Screw on a wingnut.
Step 4: Widening the Inside
To widen the inside of pipe, convert a screwdriver with a good grip into a round sanding tool:
1. Use masking tape to attach tape to the screwdriver.
2. Slowly rotate the tool into the pipe.
3. Test with batteries until they slide through easily.
Note that this process can take a long time (20+ minutes) and the sandpaper may need cleaning off with a brush.
Step 5: Sizing the End Caps
1. Screw on one of the end caps completely.
2. Put in 3 AA test batteries.
3. Unscrew the end cap until the the top most battery lies below the opening as pictured.
4. The battery should NOT be flush or protruding from the opening.
5. Use threading / plumbing tape to cover off limits threads as pictured.
Step 6: Cartridge Assembly
1 x PVC Nipple
1 x Spring
2 x End Terminals
3 x AA batteries
To color code the cartridge, use:
1 x Red Sharpie
1 x Black Sharpie
For the spring, try finding an OSH (Orchard Supply Hardware) as they distrubute Centry Springs products. You'll probably need to modify the spring a bit, so that it coils towards the center on both ends. The spring I used came from a broken solder sucker tool.
Pictured is how to assemble the cartridge from left to right, top to bottom. After this step, it's ready for testing, and can supply power through its terminals.
Step 7: Shaping Metal Clips
Each holder is 13/16" at the center rectangle with 3/4" wide wings the stretch 1 1/4".
Cutting / Shaping:
1. Use tin snips to cut.
2. Use a rubber mallet & hose clamps to have the base of the holders conform to the bicycle frame.
3. Protect the bicycle frame with masking tape.
I'm fairly certain the temperatures were too low to temper the metal, however. If you're not using a zinc-plated or stainless sheet, you can heat it up on your stove and immerse it in mineral oil. This gives it a black finish.
Step 8: Attaching Clips
1. Use friction tape to prevent pipe clamps from scratching the frame surface.
2. Use foam tape underneath the clip to prevent it from scratching the frame.
3. Use pipe clamps to secure the clips to the bicycle frame.