Why can’t my hammer drill drill a hole in concrete?

Question

I do have a hammer drill (Bauer 7.5amp, Harbor Freight) and some 1/2“ Bosch masonry hammer drill bits.

I‘m trying to drill a hole into my concrete patio. I have made it one inch deep but that destroyed two drill bits.

One drill bit tip cracked off and the second one is starting to become round. I feel like the drill has good power but the drill bits don’t hold up.

Any ideas? Should I upgrade to a rotary hammer?

Answer 1

As Tetsujin said, I'd rent an SDS rotary hammer.

Masonry bits work in 2 parts. The hammer slams the bit forward and chips a bit of the concrete, and the rotation of the bit extracts the chips and dust from the hole.

Hammer drills with a Jacobs chuck (like you have) do not really have enough hammer force. They can often get by for smaller and shallow holes, but it does not seem to be getting the job done in your instance. When they fail, they often burn up the drill bits as you have seen.

SDS rotary hammers have a completely different chuck and deliver significantly more hammer force. I've used a SDS rotary hammer to drill a couple of dozen 3/8 inch holes in concrete, and the bit barely looked worse for wear.

Answer 2

This is what solved it.

I purchased a Rotary Hammer from Harbor Freight and a 1/2" SDS Masonry drill bit (for concrete with rebar).

The difference between the hammer drill and the rotary hammer drill with the SDS drill bit is night and day. It took only a few seconds for the rotary hammer to drill the hole with no visible wear to the drill bit.

The drill bit does not need cooling (water). It only warmed up slightly. Pouring down water in the hole is also counter-productive because it is harder to extract the debris that way (I use an air compressor).

As others have mentioned, wear eye protection that fully encloses your eyes and use a dust mask.

Answer 3

Since you burned already 2 of the drills already something is wrong. That should not happened.

First do not force the drill putting all your weight on it, let it do the hammering work.

Second, most drills like to be cooled and lubricated.

That is to prevent the overheating at the tip that can get red hot which will weaken the drill tip material.

Most concrete drills work really well if you keep them wet (spray water in the hole).

Walk by a construction site and you will see them using water when drilling.

Cooling and lubricating will make your drill bit last longer.

If/when you hit iron (rebar) stop and change the drill type.

Also I would recommend the Bosh "blue granite" drills.

Answer 4

Technique is important. I learned these tips the hard way:

• Do not push hard on the tool. The pressure that affects the work is coming from the hammer action, not from you. The pressure you apply should be just enough to keep the bit from jumping away from the work area.
• If you hit a material that is too hard for your tool's hammer to break, like a big piece of stone in a concrete slab, consider starting another hole (or buying a tool with a stronger hammer). Letting your tool sit there a wail away at it may eventually help but most likely, your bit will overheat and its tip will come out looking like a pancake. Especially if you push on it.
• Keep the bit straight at all times, and make sure the tool's angle remains consistent. If the top half of your hole was created with a bent bit, then straightening it will cause the bit to rub on the sides and overheat.
• Make sure the dust is being extracted continuously. Sometimes it gets caught halfway up the hole and can cause the bit to rub or break against the pressure buildup. Extract bit, blow out the hole, continue.
• Hammer at a lower speed so you can more easily monitor dust extraction, obstacles, tool angle, heat buildup, etc.

If your bits are still overheating, then keep a spare handy so you can switch to it. By the time your spare gets hot, your first will have cooled off.

Other posters have mentioned this, and I agree: If you are drilling concrete, get a rotary hammer with an SDS-Plus bit. I was able to find a really beefy Ryobi one with a cord on Amazon for about $65.

High quality bits will definitely cost less over time, not only with heat problems but with breakage and work speed. I like Bosch bits. They make SDS-Plus bits too, called BullDog I think.