Dollfie Dream III Shoulder Reinforcement Project

About a year ago, Volks introduced the completely redesigned Dollfie Dream Type III body as a replacement to the Dollfie Dream Type II body.  The type III body promised increased articulation, the ability for the arm to hold up heavy objects, etc etc.  In a nut shell, the type III body delivered what it promised; however, at the same time, there were some design trade-off that wasn’t readily apparent to most of us at that time.  In the course of introducing new movement range and capability, the new body became weaker, reports of broken shoulder joints started circulating the internet within months of the introduction of the new body.  I have always handled my DD girls with great care and had so far been free of any incident until about a month ago when I was getting Sakuya ready for my California trip.  I noticed some cracks started to develop when I pulled her arms out to change her dress… I was devastated, my most beloved Sakuya chan now has a cracked shoulder joint!!!   It took me a few minutes to overcome my sadness, then I realize as a mechanical engineer with 16 years of working experience, I owe myself a full blown investigation!  After taking a closer look at the shoulder joint, I finally realized why we are seeing cracked shoulders…

Full scale image can be found here http://www.flickr.com/photos/wolfheinrichsworld/8126361372/in/photostream

After the close up inspection, whoever designed the new shoulder joint failed to follow the most basic design rules for a plastic boss…..

In general, the outside diameter of a boss need to be 2 times the diameter of the inside diameter…

Source: http://www.efunda.com/designstandards/plastic_design/boss.cfm

In order to withstand the hoop stress during the shoulder insertion, O_bneeds to be 2X of O_i; so let’s do a little fact checking here:

The outside diameter of the DD III Shoulder joint is 0.591″, check.

The diameter of the DD III shoulder is….. 0.320″, check.

If we follow the design rules, the outside diameter of the shoulder joint should have been 0.640″, unfortunately based on my measurement above, it failed to meet the basic design rules.  So why didn’t Volks just make the boss thicker?  Well, they already did!  The boss diameter of the prototype Dollfie Dream Sister was even smaller!!!  There are traces of tool modification still readily visible to trained eyes…. What we see right now is already an improved version, but unfortunately, it’s still not enough…. So how did Volks mess this up?  Well, there is a reason for that too, since a properly designed plastic part need to maintain uniform thickness so it’s not like they can just increase the diameter as they please.  Now, I am not making excuses for Volks, the person who designed this part need to get fired…. and there are ways to redesign this part but that’s outside the scope of this blog post.  The next obvious question that comes to mind is, how did DD II overcome this problem?  Good question, so let’s take a look at DD II.

As you can see here, while the DD II doesn’t quite meet the 2x factor, but it is still significantly better than DD III.  And upon closer inspection, the DD II design actually employ a separate reinforcement ring to increase the overall boss diameter to an acceptable level, unlike the DD III.  So, after all these talk, what can we do about it?  Excellent question!

Over the course of the past month, one of my most trusted 3rd party Dollfie Dream accessories suppliers, Cool Cat Collection Shop, the group also responsible for a huge selection of premium Dollfie Dream dresses under the Le chat de neige label came to the rescue!

DD Sakuya here wearing one of my most favorite dresses from Le chat de neige, Cool Cats Collection.

The “Fortified Shoulder Joint Aluminum Alloy Sheath“, introduced just earlier this month, is most likely one of the best after market solutions to minimize the chance of cracking due to normal handling.

As you can see here, the aluminum alloy sheath just slip over the original shoulder part, thus protecting the shoulder part from cracking.  In reality, this solution basically mimic what was already implemented in DD II.

A courtesy measurement indicate that the reinforced shoulder is now well over the 2x factor, and not to mention aluminum alloy has significantly stronger yield strength than most plastic resin. In my opinion, this reinforcement sheath is a great insurance against the weakness of the DD III body, I seriously recommend everyone to get this and help minimize any unintended damages since I strongly believe that no matter how careful you are, it’s only a matter of time before microcracks begin to develop.  A similar weakness also exist at the hip joint, but I think it’s self evident by this point that the hip reinforcement ring, also introduced by Cool Cat will only help!

In addition, Cool Cat also introduce a new DD III replacement neck joint, that works very similarly to my earlier blog post on Dollfie Dream Neck Joint Replacement.  I do believe they have thickened the neck shaft just a tiny bit to retain the head better than the DD II version.

Now Sakuya chan is all fixed up and happy ♥

That’s it for now, but next time I am going to continue my Dollfie Dream III Instrumentality Project by introducing my own custom designed components (compatible with older DDS body)!  Here is a little sneak preview!

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