Little by little, right? Choosing the wrong hammer bit can be costly and painful
Whether you're preparing to enter a career as a mason or just doing some DIY work around the house, knowing which hammer bit you'll need can make all the difference in the outcome. It's not just about knowing what diameter and depth you need to drill, it's about the makeup and design of the drill itself.
10 second summary
- Match your SDD-Plus or SDS-Max hammers with the same bit connections – they are not interchangeable
- 2-flute drill bits are good for drilling in unreinforced concrete, but tend to stick to rebar
- A 4-knife drill lasts longer and can cut through rebar, but can be damaged on impact
- Full-tip carbide drills cut through rebar without causing damage like 2- and 4-flute drills
- Collect silica dust while drilling with core drill bits, universal guards, or on-board dust collectors
Let's Talk About Rotary Hammer Bits
Round/Hex Shank, SDS-Plus, SDS-Max
If you're just setting up a couple of Tapcons, you don't need a rotary hammer. A cordless impact drill and a multi-purpose drill from Bosch can quickly complete the drilling process.
When you're stepping into more or bigger holes, that's where the rotary hammer comes into play. Modern rotary hammers have either an SDS-Plus or an SDS-Max chuck. SDS stands for "Slot Drive System".
The connection types are different and not interchangeable, so be sure to buy a drill that matches your hammer. Typically, you move from SDS-Plus to SDS-Max as the diameter of the hole you need to drill increases, although there is a lot of overlap in the intermediate diameters.
Install the cutter head
Most rotary hammer bits are of a double-blade design. Once you've ground the steel, the carbide chips are joined at the ends by a welding or brazing process to form two cutting edges. When you hear the term "embedded carbide," it refers to that type of joining process.
There is also a four-knife design. One way to make it is to place two smaller cutters on either side of the original carbide chip, making a total of three parts. The other is to start with a single cross piece and embed it. You'll see one-piece forms in newer designs.
Confused about carbide? Learn more here!
4 sides is better than 2 sides
Double-blade drills are great for quickly drilling holes in concrete. However, they are not designed to cut rebar and often get stuck when hitting rebar.
The four-knife design lasts longer and is capable of cutting rebar tied with two-knife heads. If your rotary hammer has kickback control, it helps prevent injury, but you can still damage either bit style on the rebar.
When you are drilling in reinforced concrete, the standard procedure is to switch the rebar cutting bit through the reinforced concrete and then switch back to complete the hole.
Always go for full carbide
Now there is a third option. Drills such as Bosch's Speed Xtreme use an all-carbide tip, not just a carbide tool. It creates a stronger bond and is more durable than a quad-blade. Best of all, it can bite through rebar without causing damage like other drills.
How about 6 cutting edges? 8?
We also see some manufacturers use six or more cutting edges on larger drills. According to the Bosch team, it's harder to pull out properly than a carbide tip. There's also the matter of diminishing returns — the performance benefits of those bits aren't that great compared to the added cost.
don't forget silica dust
Whenever working in concrete, be aware of OSHA's silica dust regulations. Hollow drills like Bosch's Speed Clean speed up the process by collecting dust as you build. Universal hoods and on-board dust collectors are other options that can accommodate this without additional PPE.