October 15, 2018 | Greg Everett | CAD/CAM, Workflows
For this guest blog post we've worked with Greg Everett from Sierra Dental Tool. Greg is an experienced laboratory technician and in his current role with Sierra he is dedicated to creating and sharing education focused on CAD CAM, lean manufacturing, tool selection, and more to help laboratories succeed.
As a dental lab invested in digital technology, you want to get the most from your milling burs. Let's take a look at what it takes to cause notable damage and how to avoid it. We'll shed some light on the ways milling burs can get damaged and document the scope of that damage in each scenario.
The smallest defect in the bur's cutting edge will become bigger as the bur wears. Any chip, divot, or abrasion in the bur will become a site for wear to propagate from. A damaged milling bur will work just fine for a little while, but it will certainly not last as long as a pristine one.
So, you dropped your bur... it's probably fine, right? Unfortunately, there's a good chance it sustained at least some damage. It all depends on how and what it hit. But how can you tell? To show you, I'm going to systematically destroy some milling burs and document the results.
I thought about the most likely ways for milling burs to get damaged in the lab. Here are a few that I came up with:
The only way to find out is to test it. I've designed a test to see how milling burs hold up to impacts with different materials. It'll be interesting to find out how much abuse a bur can take before it's got any visible damage. I've documented some controlled impacts of burs into various materials and show you what happens.
The idea is to simulate an impact between a bur and these materials: brass, tungsten carbide, and tile—then I'll record and share what happened.
I needed to assure that the impacts to each material use the same force. After a little bit of research, I decided the best way to do that without fancy lab equipment was to build a simple pendulum. Using the same release point for the pendulum assures a reasonably accurate repeated force.
The right amount of force is key. After much consideration, I decided to keep it simple. As a benchmark, I used the force required to chip the lead on a freshly sharpened number two pencil. I chose this because it's easy to visualize and it's repeatable.
I tested the pendulum rig with a pencil until the force chipped the tip. Then, I noted the mark that corresponds to that force. That mark is used as the drop point for all the tests.
This one is designed to illustrate the impact between a bur and the brass holder in the mill. It's easy to press the bur into the holder at the wrong angle or with too much force. It's important to be diligent with your bur installations.
Notice the significant amount of edge damage. Not only is the diamond coating chipped, but so is the carbide. This is a fairly predictable result for a carbide on brass impact. This will surely affect the longevity of the bur.
This impact simulates a scenario where a bur hits another bur. This is most likely to happen if you store your milling burs loose in a drawer. We always recommend storing your burs in the original packaging or in a specialized bur holder.
This impact didn't seem to dent the carbide very badly, but the diamond coating has certainly flaked off. Without the protection of the diamond coating in that area, this bur will surely suffer from a reduced lifespan.
Next we tested an impact on the floor by hitting a bur into a small piece of floor tile. The hardness characteristics of tile are much different from metal. Note: This may not be a perfect simulation of a floor drop because a tip impact from standing height would likely have a larger amount of force involved. However, in the interest of keeping the test fair, I've kept the force the same.
This was by far the most interesting test result. I expected the results to be similar to those of the carbide and brass tests. However, the damage sustained in this test appears to be at or greater than the damage caused by the carbide impact. This is definitely a reason to avoid dropping your burs on the floor!
After running these tests, it's become clear that any impact sustained by a bur is not good and compromises the life of the bur. By storing, handling and working with milling burs carefully you are maximizing the life of the bur and running an efficient and economic lab.