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Sunday 12 May 2024

Project 24 - Battledown Flyover #5 (disaster recovery)

The floor is in four parts. At the front of the photo is the East End and above it one of the centre sections.

The East End was printed first. The deck sides cracked and broke away as I removed the resin support structure and the deck surface is rippled and pitted. Both defects are not a show stopper because they are hidden when the bridge is assembled.

For printing, the part was angled 10 degrees for both X and Y. This is my usual setting. After further research I learnt that models with a large flat area are best printed at 45 degrees. This was set for the centre section and to my surprise fewer supports were created by Lychee and the deck printed without ripples. However, it still suffered from fractures of the deck sides and now the trapezoid plates as well. I could fabricate some infills so, still viable.

It was at this point I test fitted the deck to the two bridge sides and discovered to my horror that the width of the deck is too narrow compared to the prototype. It needs an extra 10mm. Well that was a show stopper. I had to rework the design to widen the deck and at the same time I doubled the thickness of the deck and trapezoid plates in the hope they would not fracture.

The East End floor was reprinted and came out much cleaner, except for some deformation of the bottom girder flanges, which can be corrected with plastic infills. The deformation is due to inadequate supports at the ends so, I added more to the East End floor and centre section designs. The reprinted centre section formed perfectly.

I am having doubts about using water washable resin due to its brittleness. Also, the usual method of leaving the dirty water in full sun for a couple of days to let the resin cure and fall out of the water is not too successful. The water tends to hold onto the resin. I believe IPA would separate itself more readily and whilst IPA can be used instead of water if I went that way I would probably move to a more pliable resin as well.

To Part 6


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