Disaster at Battledown #2

 More experiences using Nova3D Washable Mecha Resin.

I do like the fact that resin particles washed off settle at the bottom of the water tank rather than remaining suspended in the water.

I do not like the excessive warping that occurs in thin plate sections, which is what this bridge is mostly composed of. But, the situation seems to be recoverable.

Within minutes of being out of the print chamber and with supports still in place warping occurs that is quite worrying to see. (It's like those tinsel fish that curl up from the heat of  your palm). The material is also floppy like rubber. Even after curing in a UV light chamber for a few minutes the steady march of warping continues. I since read that warping is due to uneven shrinkage during the curing process.

What I had to do was carefully tie down components where areas have warped and then cure on a shelf in sunlight. Once fully cured the parts become hard with some flexibility that resists breakage.

These larger pieces were less problematical. Where warping was present I found heating with a hair dryer then moving and holding the warped part to the correct position until cooled eliminated the fault.

Before I started I wondered if the new imbedded handrails would print correctly. Well, they did! The two bent pieces at the end will reform when joined up to the next bridge part handrails.

The jury is out on the suitability of this resin. The next part to print could exhibit insurmountable warping due to its style requirements.

To Part 1.

A Card Kit for June

Swanage Signal Box (pre heritage)

View the Card Kit here.

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.