Polishing soft metals isn’t just about getting them to be shiny. It’s about avoiding a gritty disaster where one wrong move and your tumbling media is stuck in every hole, slot, and crevice. That’s why selecting dry tumbling grit is quite a critical decision. It is about choosing the right size, shape, and material to achieve the perfectionism you are looking for.
Opting for finishes such as burnished brass, mirror-finish aluminum, and smooth-as-glass copper requires a deep knowledge of your grit. Today, we are going to explore the grainy underworld of dry tumbling grit.
Why Grit Size is Important
If you’ve got a soft metal part, such as a brass, aluminum, or copper part, it is something beautiful that deserves better than a scratched-up, tarnished fate. You load it into your tumbler with some corn cob grit (a classic choice for dry tumbling) and expect great results. But suddenly, grit gets wedged in the slots and lodged in the holes. Cleaning this grit out is quite tedious and time-consuming. So what went wrong?
You used the same medium grit size that worked for bigger, simpler parts. Because when parts get more complex and intricate, your grit needs to get smarter, not just smaller.
The Conundrum of Dry Tumbling Grit
How will you get it right? Not too big, not too small, and just right.
Option 1: Go Big
One solution is to use larger grit. Bigger particles are less likely to get stuck in tiny spaces. They roll over the details instead of crawling inside. But is the problem solved? As that larger grit starts to break down (all grit breaks down eventually), it becomes smaller. Once it shrinks, it starts slipping into all those narrow areas you were trying to avoid. So you’re back where you started.
Option 2: Go Small
The other option is to use very fine grit. It’s so small and light that it won’t wedge into holes at all. However, fine grit lacks the weight and impact to actually burnish your metal. It just floats around, accomplishing very little. Worse, it can pack into tight spots, settling in like fine sand at the bottom of a bottle.
This is the paradox of dry tumbling grit: the wrong size makes a mess, and even the right size might not do the job well enough.
Grit, Mesh, and Microns
Grit Size: You must have seen terms like 60/90 or 500F. This is grit size and refers to how coarse the particles are. A low number (like 60) means big, aggressive particles. A high number (like 800) means fine, gentle ones.
Mesh: This is a little more technical. It refers to the screen size used to separate particles. For instance, 1000 mesh = 1000 grit. The terms are mostly interchangeable at lower grades.
Microns: They are used for ultra-fine abrasives. Unlike grit, bigger numbers mean bigger particles here. 120 grit ≈ 100 microns. 600 grit ≈ 25 microns.
To burnish brass with just the right grit, you must know these numbers well. Understand what each unit means. Dry tumbling grit is the math of metallurgy.
Choosing Your Grit Material
Different jobs call for different abrasives. Here’s a run of the grit lineup:
Corn Cob Grit
A classic for dry tumbling grit, especially with soft metals. It cleans and polishes without removing too much material. It is safe and gentle, but choose your size wisely.
Silicon Carbide
This is a hardcore grit with a Mohs rank of 9+. It is sharp and aggressive, and every break creates a new edge. It is best for rough shaping or when your metal needs quite some work.
Boron Carbide
It is even harder than silicon carbide and expensive, too. Though it is messy, it is ideal for polishing gemstones like corundum. It’s not typically used for metals unless you like to splurge.
Aluminum Oxide (Alumina)
This grit is reliable. It is sharp but controlled and great for pre-polish and final polish stages. It breaks down into rounded edges, which is ideal when you want refinement without scratches.
Cerium Oxide
This soft grit is best for glass and quartz (Mohs 5–7). It is not ideal for metals.
Tin Oxide
This grit of submicron size is used as a final polish material. It is the dry tumbling grit used for luxury treatment.
Chrome Oxide
Chrome oxide is perfect for jade and green stones. It is less common in metalwork but is a useful specialist.
Diamond Powder
A Mohs 10 grit, it sits at the apex of the grit pyramid. It is expensive and sold by the carat. Use it if you’re polishing corundum or just want to feel fancy.
Sapphire Powder
Sapphire powder is a synthetic polishing abrasive made from high-purity aluminum oxide (Al₂O₃)—the same chemical compound that forms natural sapphires. It is great for polishing hard metals and is a bit of a hidden gem in the grit world.
No One-Size-Fits-All Solution
The reality is that there’s no universal answer in the dry tumbling grit world. Every part, every project, every metal demands a custom approach. Selecting dry tumbling grit is about the balance of the following:
- What’s the geometry of your part?
- How fragile is your material?
- How polished does the final result need to be?
- How much time do you have to clean out media?
Your Grit Guide: Kramer Industries
If you are still overwhelmed, it’s time to talk to the experts at Kramer Industries. For over a century, Kramer has been the go-to source for tumbling media, equipment, and surface finishing expertise. Whether you’re working with a brass figurine, a high-performance aluminum part, or just trying to stop grit from ruining your afternoon, you will find the answers to your finishing at Kramer Industries. So, contact Kramer Industries today.
Related Articles
