A Bitโs a Bit, Right? Choosing the Wrong Rotary Hammer Bits Can Be Costly and Painful
Whether youโre 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. Itโs more than knowing what diameter and depth you need to drillโitโs about the makeup and design of the bit itself.
Article Highlights
- Match your SDD-Plus or SDS-Max rotary hammer with the same bit connectionโtheyโre 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
Letโs Talk Rotary Hammer Bits
Round/Hex Shank, SDS-Plus, SDS-Max
If youโre just setting a few Tapcons, you donโt need a rotary hammer. A cordless hammer drill and one of the Bosch Daredevil MultiPurpose bits make quick work of the hole-drilling process.
When you step up to more or larger holes, thatโs where a rotary hammer comes into play. Modern rotary hammers are available with either an SDS-Plus or an SDS-Max chuck. SDS stands for โSlotted Drive System.โ
The connection types are different and not interchangeable, so be sure to buy the bit to match your hammer.ย 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 is attached to the end to create the two cutting edges, using a welding or brazing process for the connection. When you hear the term โembedded carbide,โ it refers to that type of attachment process.
Thereโs 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.
Editorial Note: Learn about the importance of carbide in tool accessories.
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 drilling in reinforced concrete, the standard procedure involves switching to a rebar cutting bit to penetrate it, then switching back to a drilling bit to complete the hole.
Always Go Full Carbide
Thereโs now a third option as well. Bits like the Bosch 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?
Weโre also seeing some manufacturers go to six or more cutting edges on larger bits. According to the team at Bosch, itโs more difficult to pull off correctly compared to a solid carbide head. Thereโs also the issue of diminishing returnsโthe performance benefits of these bits arenโt as great compared to the increase in cost.
Donโt Forget About Silica Dust
Whenever youโre working with concrete, be mindful of OSHA silica dust regulations. Hollow core bits like the Bosch Speed Cleanย 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.
