A Bit’s A Bit, Right? Choosing the Wrong Rotary Hammer Bits Can Be Costly and Painful
Whether you’re getting ready to enter a career as a mason or just have some DIY work to do around the house, knowing what rotary hammer bits to reach for makes all the difference in the outcome. It’s more than know what diameter and depth you need to drill—it’s about the makeup and design of the bit itself.
- Match your SDD-Plus or SDS-Max rotary hammer with the same bit connection—they’re not interchangeable
- 2-cutter bits are good for drilling in unreinforced concrete but tend to bind on rebar
- 4-cutter bits last longer and can cut through rebar but might take damage when they hit
- Full-head carbide bits can cut through rebar without the same damage as 2- and 4-cutter bits
- Use hollow core bits, universal shrouds, or onboard dust extractors to collect silica dust while you drill
Let’s Talk Rotary Hammer Bits
Round/Hex Shank, SDS-Plus, SDS-Max
If you’re just setting a few Tapcons, you don’t need a rotary hammer. A cordless hammer drill and one of Bosch’s MultiPurpose bits make quick work of the hole-drilling process.
When you step up to more or larger holes, that’s where a rotary hammer comes into play. Modern rotary hammers have either an SDS-Plus or an SDS-Max chuck. SDS stands for “Slotted Drive System.”
The connection types are different and not interchangeable, so be sure to buy the bit to match your hammer. In general, you move from SDS-Plus to SDS-Max as the hole diameter you need to drill increases, though there is plenty of overlap in the middle diameters.
Attaching Cutter Heads
Most rotary hammer bits use a two-cutter design. Once you mill out the steel, a carbide chip goes on the end to create the two cutting edges using a welding or braising process for the connection. When you hear the term “embedded carbide,” it refers to that type of attachment process.
There’s also a four-cutter design. One way to make it is to place two smaller cutters on either side of the original carbide chip, making three total pieces. Another is to start with a single cross-shaped piece and embed it. You see the single piece form in newer designs.
Confused about carbide? Learn more here!
4 Edges are Better than 2
Two-cutter bits are excellent for drilling fast in concrete. However, they are not designed to cut through rebar and often bind up when they hit it.
The four-cutter design lasts longer and is able to cut through rebar where a two-cutter head binds up. Kickback control helps prevent injury if your rotary hammer has it, but you can still damage either bit style on rebar.
When you’re drilling in reinforced concrete, standard procedure has you swap to a rebar cutting bit to get through it, then back to a drilling bit to finish the hole.
Always Go Full Carbide
There’s now a third option as well. Bits like Bosch’s Speed Xtreme use a full carbide head instead of just carbide cutters. It creates a stronger bond and lasts even longer than the four cutter head. Most importantly, it chews through rebar without taking the damage that other bits do.
What About 6 Cutting Edges? 8?
We’re also seeing some manufacturers go to six or more cutting edges on larger bits. According to the team at Bosch, it’s more difficult to pull off correctly compared to a solid carbide head. There’s also the issue of diminishing returns—the performance benefits of these bits aren’t as great compared to the increase in cost.
Don’t Forget About Silica Dust
Anytime you’re working in concrete, pay attention to OSHA’s silica dust regulations. Hollow core bits like Bosch’s Speed Clean make the process faster by collecting dust as you create it. Universal shrouds and onboard dust extractors are other options to contain it without the need for excess PPE.