Dummy 13 - Fixing Loose Joints

Has your Dummy 13 been “Chalk Lined”? 
Too weak in the knees to even stand up?

After printing your Dummy 13 or other articulated model, you may have a loss in stiffness of the model when the 3D printed joints wear or stretch. This can happen even if you use PETG. Eventually the model may not even be able to stand on its own. You may also notice that the limbs, hands or feet won’t stay in a position you want them to. It’s not hard to understand why this happens. Both parts of the joint are hollow, made with various infill parameters. After a short time, both parts can stretch to seek a “normalization”. 

This happened to my prints. So I have been looking for a substance I could apply to the joints to make them stiffer. I remembered as a child, getting pine sap on my hands. It was very tacky. That’s when it hit me.

There is a simple repair!

This method can prevent new models from eventually “slipping” and the same method will restore older models to be just like new. This is done by adding a tackifier to the loosened joints and sockets.

In our case, the tackifier will be gum rosin powder. It is made from Slash Pine, native to the southern United States. By adding a tiny amount of gum rosin to the joints, it provides just enough friction to keep the model’s joints from slipping. You don’t need much. Add too much and it will be difficult to move. A light dusting is all that is needed. It’s better to add less, than to add too much.

Instructions

3D print the Rosin Applicator stl file. Add a 1 mm x 3.2 mm x 75 mm diameter rubber band as shown in the photo. You will have to stretch it to get it in the grooves.

Dip the rosin applicator tip into the gum rosin. The rubber band will pick up a small amount of rosin. Apply the rosin to the whole inside of the ball socket. Rub the applicator around the inside to distribute the rosin and apply some force to the rubber band tip, forcing the rosin into the layer lines. You don’t want any clumps of rosin. It should just look like it is covered with a light dusting. That’s it! See pictures.

Reassemble the joint and move the parts around to fully distribute the rosin. You will notice that the joint is slightly stiffer and it should stay in whatever position you move it to. If it is still too loose, then apply a little more rosin.

Happy with the results?! Let others know. Share a picture of your restored Dummy 13.

Gum Rosin

https://www.amazon.com/Creekwood-Naturals-Powdered-American-Powder/dp/B07DG1YT2V/ref=mp_s_a_1_14?crid=2JCRIFFBY8T5I&dib=eyJ2IjoiMSJ9.PXWD1yNqZTRJ_6ci83beJBJE6RNheU1bH6U0ttmTnsYZHm4MuZdmpUUfzjDv_hOIKYq4oos_qCNHHeVAr00X0jx9bLtc6SplZtSAe0t-hs7R63ubFqzDuxenOzPhGqwxYISuyV5I3E5E2MYE357FrWG619nXhq8KFHBizMHGGGH03ftReQqCteVCQGS0eUi9ndtqODnfwoQK-5zpaLHNfQ.CI-m84-EKfly5oyheMsIXJDddqvzUOhokPVjh43wFMA&dib_tag=se&keywords=pine+rosin&qid=1726782121&sprefix=pine+rosin+%2Caps%2C155&sr=8-14 

Printed with PETG.

No supports needed.

Cheers,

Printium 3D