The most common failure in a Copal motor is the first gear, the plastic gear connecting to the brass gear on the rotor axle. This one wears out first, because it makes the most revolutions.
Usually we replace it with a gear salvaged from another broken motor (or replace the motor, if that is easier).
Recently I found kkpmo.com, a Polish manufacturer of gears for model cars, trains, etc. that can make gears to measure. So I thought I give it a try and repair a motor using these gears.
Quick conclusion:
Is it possible? Yes! I fixed two motors, one from a Copal AP-110 and one from a Copal 602.
Is it easy? Not really. These gears are very, very small. But with the right tools and a steady hand it can be done.
Here are the old, the new and the parts for the Copal AP-110 motor:
And here it is in action:
And now in detail:
Step 1: order the gears
You need two gears, one with 10 teeth and the other with 40 teeth, both module 0.25 (M0.25).
You can order them here: https://shop.kkpmo.com/index.php?cat...8f483kcvldelk3
Drill hole diameter: 1.0 mm (maybe 1.2 would work, but I did not dare to try).
Width of the 40 teeth gear: 1.0 mm.
Width of the 10 teeth gear: 2.5 mm (but better check yourself as this may differ per motor).
For the material you can choose POM or brass. I used POM as I thought it would be easier to work with (and the original was plastic), but as you can read below the difficulty glueing, I’m now in doubt. Would brass be better? Not sure…
The cost is about 3 euro per gear and 6.15 euro shipping worldwide.
I got hem about 3 weeks after ordering (there is no tracking provided, just be patient).
The quality is flawless! They measure exactly as requested and fit perfectly to the the other gears in the motor.
Step 2: correct the bore diameter
I ordered the gears with 1.0 mm bore while the axis diameter is around 1.1 to 1.2 mm diameter. So you need a 1.1 or 1.2 mm drill and probably also a very small needle file. I did not have such a small file at hand, so I improvised one from a paperclip. I straightened the paperclip and then roughened it up by firmly rolling it between two large flat files.
Step 3: glue the two gears together
This step I’m struggling with.
The plastic used, Polyoxymethylene (POM), is very difficult to bond. I used superglue, and that worked, but with difficulties. For a good alignment I found it necessary to place the gears on the axis, but then too easily you also glue the gears to the axis. Lightly oiling the axis helped a bit to prevent this, but then you have to be careful not to get the oil on the contact surface. Another problem is that the glue is very fluid and capillary forces easily draw it into the teeth of the small gear, so use as little as possible. (It does not bond very well to the plastic it is easy to remove it afterwards using a needle, but it’s all extra work.)
Step 4: create spacers if needed
For one motor I created a spacer from scrap plastic (see photo above), for the other I reused part of the old gear. Later I found that you can also buy “micro shaft sleeves” from the same site.
Note that there is no need to attach them to the gears.
All and all I’m happy with the result! The method of glueing the gears needs improvement, the rest is fairly easy. I still have material for three more gears, so let’s see what a little practice will bring.
It does not run away and does not immediately stick to everything.
Comment