3D Printing a Melodica (8) – Soft sticky prints
21 October 2014
The parts have arrived…
I eventually decided to send my 3D files over to a printing company based in the west midlands of England, 3D Alchemy. I learnt from the previous test pieces that printing in plastic (ABS) would not provide the surface quality I needed, so I opted to pay twice the price and have it printed in resin on an Eden 500V printer, using Polyjet technology (resin cured with ultraviolet light).
A week later, the parts had arrived – all 34 of them, and it really was amazing to see them in their realised form, finally holding them in my hands, after months of virtual tweaking on the computer.
Soft sticky prints?
I put all the parts together, and was delighted to see that the keys work well, and the Yamaha reed plates fitted perfectly in the reed chamber. Just one problem. I noticed that the parts were a bit sticky, and seemed soft and chalky. I thought perhaps they would dry out over the next few days.
I already had a sample key made using this ‘Polyjet’ material which is strong and plastic-like, so I presumed it would harden into something similar. But when I attached the springs, which put a light pressure on the keys, I found that after a number of hours, they had all buckled. All but one – the original sample key was still rigid.
A design fault?
I contacted the 3d Printing company, who asked that I send all the parts back for them to check. They explained that these parts were absolutely fine and that it was the design of the key which needed looking at, as they had bent at the weakest point, where the thickness was just 1mm. It seems the reason the identical sample key had not bent was because it had been printed in white and not in blue. I had no idea that the two colours would produce something so different – the blue, soft, bendable and chalky, and the white, hard, rigid and smooth.
As a courtesy, they kindly offered a 50% refund for the bent keys, and applied some extra ultra violet curing on the main body and air chamber cover, to make it stronger. The parts returned with a stronger plastic-like texture, similar to the white sample key.