Which Drill To Choose?

You can be excused for being a little overwhelmed by the sheer number of different drill types that appear when you are trying to get the best drill deal.

This hub will provide some explanation of the different types to at least point you in the right direction. And help you make a good choice.

I think we all probably understand the term drill, but there is a lot of confusion regarding what some of the types (hammer, impact, etc. ) really mean. So lets explain..

Here is a brief explanation of the Impact Drill Mechanism.

There is a ratchet controlled impact mechanism built into the drill which generates the hammering action as the drill rotates. The ratchet is usually a pair of sprung loaded toothed disks. The teeth are ramped on one side and straight on the other. Thus one disc can rotate in one direction with respect to the other. However in order for this to happen it has to climb up the ramp but is resisted by the spring force. When the teeth on the disc reach the top of the ramp they drop down the straight side of the tooth causing the impact.

It is a simple but effective mechanism which relies on feed pressure to work. So under no load conditions there is no impact force, but any resistance to the drill bit turning caused by the work piece will cause the discs to climb the ramp and hence generate the impact as it drops back down the other side of the tooth.

This sort of action is ideal for drilling into masonry and concrete.

OK one of the key things here is the fact that the hammer action is dependent on feed pressure (how hard you push the drill).

Again we can call on Bosch to provide a good description of the rotary hammer process.

The rotary hammer drill is effectively a hammer power tool with a rotating option. They can be used for chiselling or drilling concrete and masonry. The main difference over the impact drill is that the rotary hammer has an electro-pneumatic hammer mechanism which produces the action independent of feed pressure. In general this provides a significant increase in hammer force (impact energy), over the impact drill, making it ideal for working with concrete and stone.

Rotary hammers are necessarily bulky and can weigh upwards of 2kg for the smallest of drills.

Key fact here is that the hammer action is not dependent on feed force.

SDS stands for 'Special Direct System' (not very helpful really :). It is a system actually designed by Bosch to allow tool-free changing of accessories (drill bits etc.). It has been adopted across the power tool industry.

Here is a brief description of how it works and what it is used for.

The SDS drill overcomes some of the deficiencies of a conventionally chucked drill. The SDS system uses specially formed drill shanks that can be inserted without the need for a chuck key to tighten things up.

The SDS drills have a longitudinally grooved shank which actually allows the drill bit to move in and out of the drill chuck by a small amount. Thus the hammering force can be applied directly to the captive end of the drill. Thus transmitting the impact force far more effectively as the chuck no longer has to move.

Here are some of the uses of SDS hammer drills.

The well engineered SDS-drill can be used for heavy weight jobs and is far more effective than the impact drill.

Typically an SDS-drill will be used for drilling through concrete, masonry, stone and engineering bricks without the need for a lot of effort by the user.

The SDS is ideal for demolition work and makes removal of tiles and fixtures a breeze.

Many SDS-drills have a lock that allows for chiselling without drill rotation. This is great for removing plaster, tiles or chasing out sockets and cable runs.

Well now you understand the different types of drill you should be able to make a better informed choice when selecting the drill for you.

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