I try to pick a drill that can drill into concrete / reinforced concrete for a non professional usage, say 1-2 holes a month. It is possible to choose between a combi drill (which usually has better torque) and a hammer drill (which usually has better speed and impact, many times torque is not even specified as if it's not important).
[Side Note: I prefer a combi drill so it can be also used for screwdriving etc]
Example of Combi Drill Parameters – Bosch GSB 18-2-LI Plus:
Max speed: 1900 rpm
Max torque: (1) 63 (2) 24 nm
Impact: 28500 bpm
Impact energy: ? J
Vibration emission (concrete): 13.5 m/s²
Example of Hammer Drill Parameters – Bosch PSB 650 RE:
Max speed: 3000 rpm
Max torque: 9 nm
Impact: 48000 bpm
Impact energy: ? J
Vibration emission (concrete): 35 m/s²
Questions:
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What parameters (torque, speed, impact, impact energy, vibration emissiom) are more important when drilling into reinforced concrete? Since many hammer drills come with relatively low torque I figured that it is less important for drilling into concrete but when I asked a representative of Bosch via email he told that torque and speed are more imporant here which left me confused.
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Does a higher vibration emission means a higher impact energy (in other words can one infer about the impact energy value by knowing the vibration emission value)?
Best Answer
It depends on what you are drilling. For small holes, (1/4"-1/2") a hammer drill is not usually enough impact in hardened concrete so any SDS style drill and bit will usually do as they have alot more impact than a hammer drill. Torque is not usually a problem.
For bigger holes 1" +/- torque begins to affect how much the bit can actually spin as it is doing its work if using a cheaper weaker drill.
For coreing holes 3-6"+ you absolutely need alot of torque to keep the bit moving and the impact becomes less important. This is why for larger holes only thin wall SDS bits exist otherwise there would be too much torque exerted on the smaller SDS shaft. The larger sizes that are not thin wall are typically SDS-MAX with alot thicker shaft for the increased torque required due to the additional contact area of the bit face and wall.
Increased impact can help speed the process on larger holes but without enough torque the bit just does not spin the teeth fast enough to let them do their job.
Another way to think of it is if you could have only torque or impact when making a hole, which one is more important? Torque. Spinning without beating you get a really slow drilled hole. Beating without spinning and you don't get a hole; you get demolition with a drill bit which is slower and not hole shaped.
Speed is not usually an issue unless you just dont have any as drilling larger holes is typically a rather low RPM endeavor.