Injection molding SPI surface finishes

Knowledge Base Appendix Injection molding SPI surface finishes

SPI Mold Finishes

Learn more about the Injection molding surface finishes, in the main article here.

Finish	*SPI standard**	Finishing Method	Typical surface roughness Ra (μm)
Super High Glossy finish	A-1	Grade #3, 6000 Grit Diamond Buff	0.012 to 0.025
High Glossy finish	A-2	Grade #6, 3000 Grit Diamond Buff	0.025 to 0.05
Normal Glossy finish	A-3	Grade #15, 1200 Grit Diamond Buff	0.05 to 0.10
Fine Semi-glossy finish	B-1	600 Grit Paper	0.05 to 0.10
Medium Semi-glossy finish	B-2	400 Grit Paper	0.10 to 0.15
Normal Semi-glossy finish	B-3	320 Grit Paper	0.28 to 0.32
Fine Matte finish	C-1	600 Grit Stone	0.35 to 0.40
Medium Matte finish	C-2	400 Grit Stone	0.45 to 0.55
Normal Matte finish	C-3	320 Grit Stone	0.63 to 0.70
Satin Textured finish	D-1	Dry Blast Glass Bead #11	0.80 to 1.00
Dull Textured finish	D-2	Dry Blast #240 Oxide	1.00 to 2.80
Rough Textured finish	D-3	Dry Blast #24 Oxide	3.20 to 18.0
As machined	-	Finished to the machinist's discretion	3.20 (with visible machining marks)

^{* : SPI (Society of Plastic Industry) standards}

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Material recommendations

Not every mold finish produces the same results with every material. Use the tables below as guidelines to select the right mold finish/material combination for your application.

Glossy finish

Material	A-1	A-2	A-3
ABS	Average	Average	Good
Polypropylene (PP)	Not recommended	Average	Average
Polystyrene (PS)	Average	Average	Good
HDPE	Not recommended	Average	Average
Nylon	Average	Average	Good
Polycarbonate (PC)	Average	Good	Excellent
Polyurethane (TPU)	Not recommended	Not recommended	Not recommended
Acrylic	Excellent	Excellent	Excellent

Semi-glossy finish

Material	B-1	B-2	B-3
ABS	Good	Good	Excellent
Polypropylene (PP)	Good	Good	Excellent
Polystyrene (PS)	Excellent	Excellent	Excellent
HDPE	Good	Good	Excellent
Nylon	Good	Excellent	Excellent
Polycarbonate (PC)	Good	Good	Average
Polyurethane (TPU)	Not recommended	Average	Average
Acrylic	Good	Good	Good

Matte finish

Material	C-1	C-2	C-3
ABS	Excellent	Excellent	Excellent
Polypropylene (PP)	Excellent	Excellent	Excellent
Polystyrene (PS)	Excellent	Excellent	Excellent
HDPE	Excellent	Excellent	Excellent
Nylon	Excellent	Excellent	Excellent
Polycarbonate (PC)	Average	Not recommended	Not recommended
Polyurethane (TPU)	Good	Good	Good
Acrylic	Good	Good	Good

Textured finish

Material	D-1	D-2	D-3
ABS	Excellent	Excellent	Good
Polypropylene (PP)	Excellent	Excellent	Excellent
Polystyrene (PS)	Excellent	Excellent	Good
HDPE	Excellent	Excellent	Excellent
Nylon	Excellent	Excellent	Good
Polycarbonate (PC)	Excellent	Not recommended	Not recommended
Polyurethane (TPU)	Excellent	Excellent	Good
Acrylic	Average	Average	Average

Standard drill bit sizes for CNC machining (conversion tables)

Tables of the standard drill bit sizes (metric, fractional inch, and wire gauge) commonly used in CNC machining.

Standard blank sizes for CNC machining (sheets & rods)

Tables of the standard blank sizes (sheets & rods) commonly used in CNC machining.