You know, I’m embarrassed to say this…but in 23 years of designing plastic products, I’ve never had to put on a drawing a definition of a polish level. I’ve always just handed a sample to the toolmaker and said replicate this, or gave it a subjective definition of “high polish” or “mirror finish”.
So, I have no clue what SPI definitions relate to a surface finish of something like a Lego Brick.
Google hasn’t come up, quickly, with a layman’s example of polish definitions.
Anyone help me out here?
Hope this helps.
Without looking at samples, Legos I would imagine are (just guessing):
SPI Finish A3 – 718H or S136 Hardness 32HRC
(Generally called “Normal Glossy” in China)
Have you also tried a Mold-Tech catalog? Usually they have texture finishes, i assume they would also have polish finishes.
That is one of the links I found when Googling about. It gives quantitative descriptions based on grit and materials used, but there is no real world comparison.
Ironically, from the descriptions, I was assuming SPI A3 was what was used for Lego blocks as well.
The mold-tech catalog I use does not have different glossy finishes. It’s more for textures and varying degrees of matte. Not sure if there’s a bigger MT catalog available, though. I think the one we had was like $400-500.
This is a concurrent thread: Mold Texture (Mold-Tech)
For a clear polycarbonate “window”, I used SPI-A2.
Then there is this handy chart,
Probably A3, usually when doing high polish you only go higher when it is a part with optical properties.
A3 finishes are more usually resistant to scratches as well compared to an A1. A1 parts are so smooth that even the slightest abrasion during handling or use will quickly scuff the surface of your plastic.
Moldtech is definitely not gloss and SPI surface definition. MT and Yick Sang are chemical etching process providing consistent surface textures.