Hammer Drill vs. Impact Driver

A hammer drill’s body style is similar to that of a drill-driver. However, a hammer drill is built to add extra power and a hammering action. The direction of force is different, though. The force of the hammer drill is applied directly to the bit as it hits the medium as if there was a hammer being smacked into the back of the drill as it presses forward, almost like a jackhammer. This helps break up a harder material with the bit tip while the spirals of the drill bit spin the debris out of the hole you create. Hammer drills are usually used for work with stone and concrete and should be used with masonry bits only.

  
There are two modes of operation on most hammer drills. In addition to its normal action, the hammer function can be turned off. This lets the drill function as a standard drill-driver for use with wood or metal. This can be useful when you are unsure what the material is you’ll be drilling – if, for example, you are unsure if there is wood or concrete behind a wall – but since a hammer drill is more expensive and heavier than a standard drill, it would not be an advisable tool for lighter household tasks.

Brushed vs. Brushless

One major consideration when choosing an impact driver or a drill-driver is to get a tool with a brushed or brushless motor. Due to friction produced in its operation, a brushed motor is slightly less efficient than its brushless counterpart. Brushless motors operate with without friction, leading to a number of benefits: more power going to the tool, precision motor and power control, more battery run time, less heat generated during use, and a longer-life battery. In addition, brushless stools require less maintenance. Due to the friction produced by contact, the parts in a brushed tool may occasionally need to be replaced. However, these advances in brushless technology come at a higher cost.
  
If your tools will get heavy and regular usage, investing in brushless may be a great value in the long run, but if you only break out your tools box for occasional household and DIY projects, brushed tools can serve you well and save you upfront costs. See our guide on types of drills for more information. 

Drill, Impact Driver or Hammer Drill

In all, when looking at an impact driver versus a standard drill-driver, the answer to the common question of which type to purchase is both. For the avid DIY-er, they can be valuable additions to your toolbox to help tackle a wider array of projects. Anyone who works extensively with masonry, either professionally or as a hobby, can benefit from owning their own hammer drill.

The two types of drills are sometimes sold together in combo kits which can be a great way to acquire both at a good value. 

-- Home Depot (USA)