Disaster at Battledown - again

'Again', because previously I clumsily destroyed the signal at Battledown. This time there is a bigger disaster.

When I built the flyover bridge I used wire for the handrails (visible in the photograph). These were cyanoacrylate glued to the struts here and there (it looked great). Over time the wire between fixing points had become distorted and the plastic cracked at some fixing points.

Clearly the temperature coefficients of plastic and wire being different lead to stress during changes in ambient temperature between summer and winter.

I decided to replace the wire handrails with 3d printed versions using the same plastic resin. It was difficult gluing the new handrails in place, due to access restrictions and the use of cheap cyanoacrylate glue that did not want to stick. Nevertheless, I did get them fixed on one side of the bridge.

The nearside was even more difficult as I had to lean over the bridge to view the inside face. Positioning myself precariously I slipped and fell onto the bridge which caused the side to break away.

What to do about it?

I had never been happy with my choice of 3d printing resin (Anycubic Water Wash Resin +) as it produces very brittle models and tends to warp. It may be ok for 'blocky' models but not for those with a lot of thin plate sections. This, together with the replacement handrails that still drooped between fixings (see photo), I decided to remake the bridge using a better suited resin.

First though, I changed the design to integrate the handrails such that they are fixed to every strut. Also, I thickened some girder plates to reduce (in theory) warping.

With regard to resin choice I would like to keep the water washable aspect. I came across a review comparing several water washable resins. The one that gave the best toughness combined with good pliability was Nova3D Washable Mecha Resin.

First thing I noticed was the greater viscosity compared to Anycubic. Also, the resin does not run off the prints so well resulting in a little more waste to wash off. 

I first printed a batch of small bridge components (cross bracings) that were quick to print so that I can check the results before printing more complex components.

They printed perfectly and after curing in the sun for an hour the supports were cut away. Improved pliability was evident but I still managed to break leg(s) off quite a few whilst removing the supports. This might be because the the parts are very thin (0.33mm).

To Part 2.