I recently inherited several sets of broken venetian blinds (children and the elderly are hard on venetian blinds). Most of them were easy to fix - but one pair took a some thinking to repair.
The stub for the adjustment "wand" had broken inside the gearbox. When I talked to friends they all had different ideas about how it could be fixed. I realized this seemingly simple repair was trickier than most people realized.
Ideas for repair (and problems) included
- Superglue (would break just like the original)
- E6000 (magic stuff, but not for this project)
- Tape (not enough shaft left to adhere to)
- Sleeve (again, not enough stub left to get a bite on)
- Screw (would unscrew or pull out)
- 3d printing (fun, but a lot of trouble to measure)
- Ordering replacement parts (no clue who made it)
I thought a simple "key slot" with a new insert would work, and be easy to make. But when I tried to explain my idea, I found the concept of a key-slot was unknown to my friends. And I also noticed it sounded more complicated when I used words to describe it. Even photos didn't explain it well.
So I decided to do an illustrated guide using Fusion 360.
Step 1: Identify the Problem
These blinds used a common worm-gear mechanism to rotate the main shaft. The spiral worm-gear is operated by rotating a short stub that extended from the gear. The gear/stub sits inside a gear-box. Both the top of the gear and the area where the stub and gear meet had a groove cut into them so that the part would ride securely in a groove in the case. This kept the gear/stub in place, but it also made the connection very weak - the stub's shaft was only 1/4" thick. And instead of nylon or PETG, this stub/gear was made of a brittle, clear acrylic. The shaft stub had sheared and broken completely off after only a few uses.
I had to find a way to either reattach the stub, or find a replacement for the stub. Originally, I intended to cut a tabbed slot in both the gear and stub, then epoxy them back together with a flat-bar stiffener inside the slot. But after feeling the way the plastic cut, after just a few seconds of cutting into the brittle plastic, I decided it would just break again at another spot.
So I stopped and rethought the solution. I knew I had to have some kind of key-slot mechanism. Otherwise the two parts would just rotate around the central shaft. But a full slot would weaken the structure too much. Maybe if I just drilled a tiny though-hole and cut a shallow key-way on both sides (top/bottom) of the gear it would remain strong enough. Then just run a wire through the hole and bend the ends to fit in the keyway.
I tried it - the plastic gear held together and the wire is stiff enough to remain snuggly in place while operating.
Step 2: Extract the Parts
With this set of blinds, the gearbox was wedged into the top channel (trough / head-rail / valance?) of the blinds and one edge was clipped onto one edge of the channel. Every style of blind is slightly different, so you might also need tpo remove screws or clips.
To remove this gear-box I had to pull apart the two sides of the trough to dislodge the gear box, then dislodge one of the "spools." This freed the gearbox enough so that I could pull the wand-stub out of the penetration, then remove it from the main shaft.
Three screws held the gearbox together. Once I unscrewed the cover I could simply lift out the gears.
Step 3: Drilling and Key-Slot
Remove the worm gear from the case. Hold it securely in a vise or sturdy pair of pliers. Be sure it's secure while you drill.
Use a drill or Dremel and a very small drill-bit, Create one hole all the way through the gear. This hole should be slightly off-center.
Now drill a shallow slot on both ends of the gear. You need these slots. They act as keyways, keep the parts rigidly connected and prevent the parts from rotating around each other. Without the slots, the wire will simply rotate inside the gear without turning (driving) the gear.
Step 4: Wire Connector
Cut a piece of stiff wire. I used copper wire, but aluminum art-wire (armature) or a coated wire would probably look better.
Basically, you bend the wire to form a big loop with the ends sitting in the slots you just drilled. The long end of the loop will be attached to the adjustment-wand, so be sure the wire is long enough to protrude from the upper trough of the blinds once it's installed in the gear-box.
Bend one end of the wire into a small shepherd's crook. Fit the wire through the hole and seat the end of the bent part into the slot.
Keeping the bent wire seated in the top slot, bend the other end of the wire until the other end also rests in the slot that is on the opposite end of the gear.
Reinstall the gear into the gear-box.
Reinstall the gear-box onto the main-shaft and position it into the upper trough.
Be sure the new wire loop extends far enough to attach the wand.
Snap the gear-box, spools and shaft back into place.
Attach the wand to the new wire loop and reinstall the blinds.
If you want to, you can place a short piece of drinking straw or another kind of sleeve over the wire to hide it and make it look more professional.
That's it - the repair is done and you can once again control the sun... well kind of.