Canon i80 Bubble Jet printer gear fixed
We hadn't used this portable printer much, but then I came up with an application. On testing, it started to work, then made terrible noises. Others have seen the same cracking failure of the two-part metal-nylon paper-feed gear (e.g. http://youtu.be/HvR47ZOuYNA). I believe the manufacturer forgot to allow for shrinkage of the nylon. The core is metal, and the plastic became stressed as it shrank down around the core. It was okay for a few years, but eventually the stress pulled the gear apart.
There is some mechanical repair information available online, but no schematics or other electronic repair guidance. Since it was electrically functioning, I just had to try a mechanical repair. I am very pleased with the results.
How I fixed the gear
1) Stop-drilled stress relief holes at the ends of three cracks: the main one and two others I found under a microscope.
2) Extracted the metal core (the stop holes allowed me to manipulate the plastic without growing the cracks). I measured the core and estimated how much to reduce its diameter to allow the crack gap to close, starting with 2% from the shrinkage tables for nylon.
3) Ground the core down from 12.7 mm to 12.3 mm. Ground the taper on both ends. Found that I needed to deepen three vertical grooves as well. Reamed out the plastic part to give more relief. This took 4-5 fittings; the cracks didn't get much worse and the part stayed together. I was satisfied when the crack closed under light pressure and there was still enough friction in the core (due to the three grooves) to drive the gear.
4) Drilled holes across the gap and closed them with dental ligature wire, with the twists in a groove on the metal gear side.
How I got the gear off
Getting to the gear isn't easy. I found some helpful info from the Parts Catalog (photos show some part relationships) and Service Manual (some advice on assembly).
http://elektrotanya.com/canon_i_80.zip/download.html
I suggest you take photos as you work to help identify what goes back where. I turned the printer over once, and parts fell out. My photos showed me where they belonged.
1) Remove three hinged lids by bending them in the middle slightly.
2) Remove Bluetooth adapter if present.
3) Remove screws at back.
4) Remove screws at front edge.
5) Press lock tabs and remove dark plastic corners at back.
6) Press lock tabs and pull up on top cover from the back.
7) With top cover partially open, use a tool to press on the lock tab under the paper feed button in the center section and lift the cover toward the front.
Getting to the gear means taking the chassis out only partially. Stop dismantling as soon as you have access to the gear. That way, you can avoid dealing with all the many connectors and cables.
8) Untape the Bluetooth socket's cable where it's attached to the bottom case.
9) Remove the paper lifting plate. Looking from the back, on the left side there is a latching tab. Press the pin toward the outside and swing the lever to the back. Release two springs and pull the plate out. (Service manual advises replacing it with small tabs above paper return tabs. I didn't see them. Maybe it depends on the state of the machine at shutdown.)
10) Under the battery, there is a metal shield. Untape the wires passing over it, then remove four screws at plastic tank, center back edge of plate, forward and down near circuit board, and on the right above the USB port. Pull out the shield enough to remove another screw on the right at bottom that anchors a bracket to the base.
11) There are two release tabs. From the back, one is on the left, inside next to the carriage motor (revealed under the removed lifting plate), and the other is on the right, outside between the USB port and the brass motor gear. Also pry the shell away from the power connector, and now you can lift the back of the chassis out of the case, and pull back slightly to free the front edge. Just lift it enough to get the gears clear of the case and prop it up.
12) Pry the right gear off its shaft.
13) Use fine-tipped tools to open and release the plastic split ring holding the cracked gear on its shaft. (I use dental tools.) Maybe add some tape over the work area to reduce its fly-away range. I did find mine eventually, but Canon considers it throw-away.
14) You can now slide off the gear, helping the cogged belt slip off the metal core on the inner side. Take a photo of the area; to put the gear back, you may have to remove and reassemble the cogged belt's idler pulley.
If you have questions, please contact me.