How Do I Achieve Proper SPI Mold Finish Standards?
To achieve proper SPI A1 or SPI A2 surface finishes, follow the steps outlined below with Falcon Tool finishing stones, diamond compounds, miniature brushes, and felt and rotary tools. When you follow these steps closely and consistently, you will routinely achieve proper SPI mold finish standards.
SPI Surface Finish Chart
Refer to the SPI Surface Finish Chart to determine the ideal tools and finish for your application.
Step-by-Step Guide to Achieving Proper SPI Mold Finish Standards
We list 11 steps here, but several of them are reminders to clean the surface as it is essential to do so between each step. Without proper, thorough cleaning between steps, you run the risk of residue carrying over and causing problems throughout the process.
1. Find a clean area of the shop.
You want an area far away from other machining and polishing operations. Dust and grit floating around can have a massive negative impact on the final finish during the metal polishing process. Do your mold polishing away from any airborne dust and debris.
2. Bring all stoning marks to a 600 grit or finer finish on the mold surface.
The type of metal, amount of material, and condition of your mold determine the type of finishing stones required to get your stoning marks to 600 grit or finer. This will achieve an SPI C1 surface finish. Take a look at our finishing stone application chart to determine which abrasive stone you should be using.
3. Clean the surface of your tool between each step.
Use Polishing Lubricant & Diamond Thinner with a very soft tissue to make sure your tool surface is clean. You don’t want any residue left behind and carrying over into the next step. We can’t stress this enough. This is essential.
4. Remove the stoning marks.
Use a miniature brush on a rotary tool with Grade #30 Mahogany or Grand #15 Brown Diamond Compound. Polishing Lubricant & Diamond Thinner will thin the slurry to extend the life of the diamond compound. Use a slow speed (5,000-15,000 RPM) in a rotary pattern, applying light pressure to the mold surface. Heavy pressure can over-stress the mold surface and lead to a condition called orange peel.
5. Completely clean the mold surface.
Use Polishing Lubricant & Diamond Thinner with a very soft tissue to eliminate unwanted scratches.
6. Remove the brush marks from the mold surface.
Use a medium-to-hard Mandrel Mounted Felt Bob with Grade #15 Brown or Grade #9 Red Diamond Compound to remove all brush marks on the surface from the previous steps.
7. Completely clean the mold surface.
Remove all previous-grade diamond compound used.
8. Move to the next polishing level.
Use a Grade #9 Red Diamond Compound or Grade #6 Yellow Diamond Compound with a felt bob, stepping down to a medium or soft felt.
9. Completely clean the mold surface.
Remove all previous-grade diamond compound used.
10. Achieve SPI A2 finish.
Using a soft felt bob with a Grade #3 Green Diamond Compound, you will reach an SPI A2 finish on the mold surface.
11. Achieve SPI A1 finish, if desired.
If you need an SPI A1 finish, of course the next step is to once again completely clean the mold surface. Then, use a Grade #1 Blue Diamond Compound or Grade #1/2 Grey Diamond Compound with a soft felt bob to get your SPI A1 finish.