Ad Hoc Tumbling Group

Ad Hoc Tumbling Group Message

Date: Tuesday, March 18, 2025
Time: Social Time 7:00 pm, Meeting Starts at 7:30 pm
Speaker: Group Discussion
Topic: Grit
Location: Virtually via Zoom Link sent to members via email

The 2025 GMS Rock Tumbling Contest is well underway, with participants diligently transforming rough stones into polished gems. Tumblers are churning, and anticipation is building as the May 1st 2025 deadline for submitting your tumbled masterpieces fast approaches!

Beyond the excitement of the contest, I take this opportunity to answer the age-old question that echoes through the hallowed halls of rock tumbling: What's the best grit for tumbling rocks?

The topic surfaced during a recent GMS field trip, highlighting the diverse approaches and opinions within the rock-tumbling world. It's a question that can spark lively debate, as the "best" grit is often subjective and dependent on a variety of factors, including:

The type of rock tumbled: Softer stones require finer grits than harder materials.

Individual tumbling preferences: Some tumblers prefer a slower, gentler approach, while others aim for a quicker process.

The desired level of polish: Achieving a mirror-like shine requires a different strategy than simply smoothing rough edges.

While there's no single definitive answer, here's a breakdown of the common grit stages and their general purposes, which can help guide your grit selection:

Coarse Grit (typically 60-90 Silicon Carbide): This is the workhorse of the tumbling process, used to aggressively grind down rough edges, remove imperfections, and shape the rocks. It's crucial for creating a smooth, rounded form.

Medium Grit (typically 120-220 Silicon Carbide): This stage refines the shaping from the coarse grit, smoothing out scratches and preparing the rocks for polishing.

Fine Grit (typically 500-600 Silicon Carbide or Aluminum Oxide): This grit continues the smoothing process, removing any remaining pits and scratches. It’s a critical step towards achieving a smooth, pre-polished surface.

Pre-Polish (Typically Aluminum Oxide): This stage prepares the rocks for the final polish. It further refines the surface, minimizing tiny imperfections that can detract from the final shine.

Polish (Various, including Aluminum Oxide, Cerium Oxide, Tin Oxide): This final step brings out the luster and brilliance in your stones. The type of polish used often depends on the specific rock being tumbled.

Ultimately, the best grit for you will depend on experimentation and personal preference. Don't be afraid to try different grits and techniques to discover what works best for your rocks and your desired outcome.

As the 2025 GMS Rock Tumbling Contest nears its conclusion, remember to carefully consider your grit choices and strive for that perfect tumble. Good luck to all contestants! We eagerly await the unveiling of your polished creations.

Curious to learn more? Join our ad-hoc Tumbling Group Zoom meetings! We gather on the 3rd Tuesday in January, March, May, July, September, and November to share ideas, tricks, and stories from our experiences. Be part of this exciting community where every stone has a tale waiting to be told!

Tim Hellinger
Co-Chair (co-chair open volunteers)