I've decided to share with you guys what Dottor Walkman has decided to share with me. I hope I can interpret his descriptions well enough. I think it would be selfish to keep it to myself especially since I think there is much to be learned and one can never know enough and I certainly believe there is much to be learned from this.

Of course, every collector knows the Sony WM-DD series of cassette players. Wonderful players, no doubt about it. Over the years, they have proven themselves to be as reliable as it gets, which is even more true and relevant in the world of today, where quality has gone downhill no matter where you look. All of this would be great if there wasn't for one fatal flaw and it is, of course, the failure of the center mechanical gear. The reasons for this phenomena lie in the aging process of the plastic mold, or better said, material fatigue. Cyclic repeated load on the material as well as changes of the amterial properties, the most important one being tensile/compression strength, that happens over time cause breakage of the plastic gear rim. This can also be endorsed by temperature influences, especially lower temperatures, that make the material stiffer and unable to extend to accomodate the far more rigid and temperature-stable inner metal part. Anyway, I won't be discussing material resistance theory here but rather talk about the ways to resolve this serious problem.

So, let's begin! On the first picture you can see a standard center gear of the Sony WM-DD series player, in this case a WM-DC2, that has cracked. The crack is obvious and is approximately 2-3mm in length. The situation looks rather desperate, don't you think so?

The cracked center gear.

The second picture shows two broken gears as the subject of this procedure. As you can see, the picture also shows all the necessary tools to perform this complex task:

The necessary tools to perform the task.

Voila! The gear has been successfully put together. This can easily be understated as an easy task. To perform this procedure and to perform it accurately, you need the special tools and the knowledge to use them. Treating the very soft plastic mold is nothing like wood, alumium or steel work and you need good craftsmanship to carry this out. Dottor Walkman does not use any kind of epoxy molds to insert into the cracked rim but a composite plastic mass. The composite is a two-component material based on cyanide-acrylic mixture that has appropriate mechanical properties such as strength and chemical properties such as cohesiveness. This makes the procedure much more complex but the end result makes it worthwhile. This also means the differences from gear to gear are a lot more consistent.

The crack filled with cynice-acrylic composite.

Now that we have repaired the gear and made sure it's condition is no less than excellent, it looks like this one.

The center gear, precisely repaired.

If you thought this is everything, you thought wrong. Since every serious collector is an enthusiast (in some cases this is really an understatement), we don't do the things we do just for the function, we do it for the soul. That's why the gear has to be painted. Black paint that is fade-proof and resistant to mechanical loads such as the ones that happen in a gear transmission system is used and it is looking beautiful.

The gear, painted.

In the end, the gears are not complete untill they are returned to their owners, in this case, two DC2 cassette players. This picture shows a disassembled DC2 with unpainted gear installed...

Disassembled DC2 with unpainted gear installed.

... and this one shows the other DC2 beauty with a painted gear installed.

The DC2 beauty with a painted gear installed.

Finally, you can see an interesting animation with all the three stages of the center gear:

I think this is very impressive work to say the least. Enthusiasm is always a good place to start but as we all know, it is not really enough and it takes a lot more to accomplish this. The level of experties Dottor walkman shown here (and showed on several occasions before, and on other types of equipment) really makes me change my perspective on things. As part of my profession I am bound to know mathematics and structural design but still, I could not carry this out. Not in a million years.

Here are two examples of Dottor Walkman's amazing work on the DD center gear.

The gears have been restored to a point of being equal to new. In fact, eliminating the tension stress along the rim will ensure longer service life than the original gear had.

The composite material used is not commercially available, only the chemicals, and as far as I know, Dottor Walkman is the only one using it. The composite has excellent mechanical properties such as strength (it is an isotropic material so strength applies to both tension and compression) and chemical properties such as cohesiveness. In short, when hardened it will ensure long term reliability and stability with respect to mechanical and temperature load.As can be seen, the material is formed and finishd to marginal tolerances which is quite remarkable.

If someone is interested in restoring center gears for the DD series, I am sure Dottor Walkman would be happy to do it for you.

In addition, I would like to post a link to a video Dottor Walkman has made where he is showing the two DC2 machines in question. The one on the left has the unpainted gear installed and the one on the right has a painted gear installed. My italian is terrible but I was able to understand the most, I hope you will too.

I hope everyone is doing well and as much as I would like to say thank you to Dottor walkman, I also have to thank Plop and Renzgi to their contribution to my peace of mind.

Cheers guys and cheers Dottor Walkman!

Article by stereo2go's user Tuna. Originally published here.