Impossible repairs: Fixing a broken tail

In another post, I said that it's not possible to repair any welded joints in the dinosaur's skeleton. The only viable exception to this, out of necessity, is the tail.

Here's a side view of the tail of a dinosaur, one of the small two legged versions that forms the basis of the Velociraptor, Dragon, Dilophosaur, Spinosaur etc:

Let's have a close up look at how the tail attaches:

There's a screw head which sits in a hole at the top and a wing screw which holds the tail on at the bottom. The tail itself has a long thin plate with two wires welded to it. This is a fine example of poor design combined with poor engineering creating a component that is simply built to fail.

As you walk along in your dinosaur, the tail swings from side to side. It's even a feature of the puppet and audiences love it. Every time the tail swings, the metal wires flex, and they flex around the weakest, stiffest point which is the weld on the back of the nut that the top screw head goes into.

Eventually, the wire snaps by the weld.

This is also a good example of how much extra strain is imposed on the skeleton when the foam and skin are added. The broken wire ends up about 3cm away from the weld. It's now impossible to repair the weld directly and if you did, it would simply break again anyway for the same reason. Welding the tip of a wire onto the back of a nut is a really, really bad idea. It couldn't have been any weaker unless they had made the whole thing from wet spaghetti. You can see from this photo that the wire is welded onto the back of the nut and the nut is welded to the steel plate with three tiny spot welds.

What it really needs is an articulating joint, a joint which moves and allows the tail to swing without stressing the joint.

The solution is to introduce an additional mild steel bracket to bridge the gap between the mounting plate and the broken top wire. This also has the benefit of providing flexibility at the point of greatest stress.

Mild steel is relatively soft, easy to work with, easy to weld and flexible. It will bend a lot before it breaks, and you can see stress marks forming when it's reaching breaking point which makes it possible to predict failures. The stainless steel that is used to build the puppets will break suddenly and without warning.

Think of it like the strain relief on the charging cable for your phone or laptop - the thicker section of wire at the point where the wire is most likely to bend and break.

The L shaped bracket is simply positioned in the gap between the mounting plate and the broken wire and welded where you can see the orange sections.

If you're wondering how to get round the problem of the foam catching fire then you pretty much can't. You can only reduce its impact. My approach is to wet the foam around the weld with water and then cover all the exposed foam with something heatproof such as aluminium foil or a glassfibre mat that a plumber would use to protect your skirting board from their gas blow torch when fitting a radiator valve. Then, weld quickly and keep a lot of water on hand. You'll be surprised at how quickly the foam catches fire. I'm surprised at how they get these things past import safety regulations.